U.S. patent application number 17/701284 was filed with the patent office on 2022-09-08 for apparatus and method for providing enhanced heat transfer from a body.
The applicant listed for this patent is Zoll Circulation, Inc.. Invention is credited to Ben F. Brian, Leo A. Chin, Edward W. Hollmen, Mark A. Logan, David J. Scott, Daniel W. Seegars, Lloyd F. Wright.
Application Number | 20220280337 17/701284 |
Document ID | / |
Family ID | 1000006351809 |
Filed Date | 2022-09-08 |
United States Patent
Application |
20220280337 |
Kind Code |
A1 |
Scott; David J. ; et
al. |
September 8, 2022 |
APPARATUS AND METHOD FOR PROVIDING ENHANCED HEAT TRANSFER FROM A
BODY
Abstract
Methods and apparatuses for temperature modification of a
patient, or selected regions thereof, including an induced state of
hypothermia. The temperature modification is accomplished using an
in-dwelling heat exchange catheter within which a fluid heat
exchange medium circulates. A heat exchange cassette is attached to
the circulatory conduits of the catheter, the heat exchange
cassette being sized to engage a cavity within a control unit. The
control unit includes a heater/cooler device for providing heated
or cooled fluid to a heat exchanger in thermal communication with
the fluid heat exchange medium circulating to the heat exchange
catheter, a user input device, and a processor connected to receive
input from various sensors around the body and the system. A
temperature control scheme for ramping the body temperature up or
down without overshoot is provided.
Inventors: |
Scott; David J.; (Redwood
City, CA) ; Brian; Ben F.; (Menlo Park, CA) ;
Wright; Lloyd F.; (Hopewell Junction, CA) ; Chin; Leo
A.; (Poughquag, NY) ; Hollmen; Edward W.;
(Poughkeepsie, NY) ; Seegars; Daniel W.; (Salt
Point, NY) ; Logan; Mark A.; (Pleasant Valley,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Zoll Circulation, Inc. |
San Jose |
CA |
US |
|
|
Family ID: |
1000006351809 |
Appl. No.: |
17/701284 |
Filed: |
March 22, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16231551 |
Dec 23, 2018 |
11311414 |
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17701284 |
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15063326 |
Mar 7, 2016 |
10195075 |
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16231551 |
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14462452 |
Aug 18, 2014 |
9278024 |
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15063326 |
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12897637 |
Oct 4, 2010 |
8808344 |
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14462452 |
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11413564 |
Apr 27, 2006 |
7806915 |
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12897637 |
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60695800 |
Jun 29, 2005 |
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60594662 |
Apr 27, 2005 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 2007/0054 20130101;
F28D 2021/005 20130101; A61F 2007/0093 20130101; A61F 2007/0095
20130101; F28F 2280/02 20130101; A61F 2007/126 20130101; A61M 1/369
20130101; A61F 7/12 20130101; A61M 2205/3372 20130101 |
International
Class: |
A61F 7/12 20060101
A61F007/12; A61M 1/36 20060101 A61M001/36 |
Claims
1. (canceled)
2. A patient temperature management system for adjusting the
temperature of a patient, the system comprising: a heat exchanger
configured to change a body temperature of the patient, the heat
exchanger comprising heating or cooling device that is placed
externally on the patient; a primary fluid circuit comprising a
device for heating or cooling fluid of the primary fluid circuit; a
secondary fluid circuit in fluid communication with the heat
exchanger and in thermal communication with the fluid of the
primary fluid circuit; a temperature sensor configured to provide a
signal representative of the body temperature of the patient; and a
controller configured to receive the signals from the temperature
sensor to control the heat exchanger, the controller configured to
perform operations comprising: obtaining a user input indicative of
a target temperature for the patient; obtaining an upper
temperature threshold relative to the target temperature for the
patient; obtaining a lower temperature threshold relative to the
target temperature for the patient; obtaining, based on the signal
from the temperature sensor, temperature data representing the body
temperature of the patient; based on the user input, determining a
mode of operation for the heat exchanger, the mode of operation
being for at least heating the patient, at least cooling the
patient, or neither heating or cooling the patient by the primary
fluid loop, the mode of operation being a first mode of operation
selected from a plurality of modes, each mode of operation
corresponding to a portion of a heat exchange therapy; based on the
first mode of operation, causing the heat exchanger to add or
remove heat from the patient to reduce a difference between the
body temperature and the target temperature; determining that the
patient temperature is between the upper temperature threshold and
the lower temperature threshold responsive to causing the heat
exchanger to add or remove heat from the patient; and in response
to determining that the patient temperature is between the upper
temperature threshold and the lower temperature threshold, updating
the first mode of operation to a second mode of operation that is a
next portion of the heat exchange therapy.
3. The system of claim 2, wherein the heating or cooling device
that is placed externally on the patient comprises a pad.
4. The system of claim 2, wherein the heating or cooling device
that is placed externally on the patient comprises a blanket.
5. The system of claim 2, further comprising a user interface
configured to display the target temperature.
6. The system of claim 2, further comprising a user interface
configured to display the body temperature.
7. The system of claim 2, further comprising a user interface
configured to display a cooling or warming rate.
8. The system of claim 2, further comprising a control panel that
enables modification of the target temperature.
9. The system of claim 2, further comprising a control panel having
at least one alarm button.
10. The system of claim 2, the operations further comprising
receiving the signal representing the body temperature from the
temperature sensor, and causing an alarm to be sounded.
11. The system of claim 2, further comprising a cassette receiver
which includes an internal cavity to receive a heat exchange
cassette.
12. The system of claim 2, further comprising a fluid circuit
including at least one valve, wherein the controller is configured
to open or close the at least one valve to control fluid flow in
the fluid circuit.
13. The system of claim 12, wherein the valve comprises one of a
quick connect valve or a quick shut-off valve.
14. The system of claim 2, further comprising a reservoir in fluid
communication with the primary loop, the reservoir configured to
store heat exchange fluid that is heated or cooled to the target
temperature for the patient.
15. A method for adjusting a temperature of a patient, the method
comprising: obtaining, by a controller, a user input indicative of
a target temperature for the patient, the controller being
configured to receive signals from a temperature sensor and control
a heat exchanger in a secondary fluid loop that is in thermal
communication with the primary fluid loop, the heat exchanger being
configured to change a body temperature of the patient, the heat
exchanger comprising a heating or cooling device that is placed
externally on the patient; based on the user input, determining, by
the controller, a mode of operation for the heat exchanger, the
mode of operation being for at least heating the patient, at least
cooling the patient, or neither heating or cooling the patient by
the secondary fluid loop, the mode of operation being a first mode
of operation selected from a plurality of modes, each mode of
operation corresponding to a portion of a heat exchange therapy;
based on the first mode of operation, causing the heat exchanger to
add or remove heat from the patient to reduce a difference between
the body temperature and the target temperature; determining that
the patient temperature is between an upper temperature threshold
and a lower temperature threshold responsive to causing the heat
exchanger to add or remove heat from the patient; and in response
to determining that the patient temperature is between the upper
temperature threshold and the lower temperature threshold, updating
the first mode of operation to a second mode of operation that is a
next portion of the heat exchange therapy.
16. The method of claim 15, wherein the heating or cooling device
that is placed externally on the patient comprises a pad.
17. The method of claim 15, wherein the heating or cooling device
that is placed externally on the patient comprises a blanket.
18. The method of claim 15, further comprising receiving, by the
controller, a signal representing the body temperature of the
patient from the temperature sensor; and causing, by the controller
in response to the receiving the signal, an alarm to be
sounded.
19. The method of claim 15, further comprising receiving, at a
cassette receiver, a heat exchange cassette in an internal cavity
of the cassette receiver, the heat exchange cassette being
connected the heat exchanger.
20. The method of claim 15, further comprising controlling, by the
controller, a fluid circuit including at least one valve by opening
or closing the at least one valve to control fluid flow in the
fluid circuit.
21. The method of claim 15, wherein a reservoir is in fluid
communication with the primary loop, the method comprising storing,
in the reservoir, heat exchange fluid that is heated or cooled to
the target temperature for the patient.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 12/897,637, filed Oct. 4, 2010, now U.S. Pat. No. 8,808,344,
which is a continuation of U.S. application Ser. No. 11/413,564,
filed Apr. 27, 2006, now U.S. Pat. No. 7,806,915, issued Oct. 5,
2010, which claims benefit to U.S. Provisional Application No.
60/695,800, filed Jun. 29, 2005, and U.S. Provisional Application
No. 60/594,662, filed Apr. 27, 2005, the entireties of which are
hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to medical devices
and methods and, more particularly, to a programmable,
microprocessor based controller and method for controlling the
temperature and flow of a thermal exchange fluid that is circulated
through a heat exchange catheter inserted into a patient's body for
the purpose of cooling or warming at least a portion of the
patient's body.
BACKGROUND OF THE INVENTION
[0003] Under ordinary circumstances, the thermoregulatory
mechanisms of a healthy human body serve to maintain the body at a
constant temperature of about 37.degree. C. (98.6.degree. F.), a
condition sometimes referred to as "normothermia." To maintain
normothermia, the thermoregulatory mechanisms act so that heat lost
from the person's body is replaced by the same amount of heat
generated by metabolic activity within the body. For various
reasons such as extreme environmental exposure to a cold
environment or loss of thermoregulatory ability as a result of
disease or anesthesia, a person may develop a body temperature that
is below normal, a condition known as "hypothermia." A person may
develop a condition that is above normothermia, a condition known
as "hyperthermia", as a result of extreme exposure to a hot
environment, or malfunctioning thermoregulatory mechanisms, the
latter being a condition sometimes called "malignant hyperthermia."
The body may also establish a set point temperature (that is, the
temperature which the body's thermoregulatory mechanisms function
to maintain) that is above normothermia, a condition usually
referred to as "fever." The present invention addresses these and
other situations requiring alteration of at least a portion of a
patient's body temperature.
[0004] Accidental hypothermia is generally a dangerous condition
that may even be life threatening, and requires treatment. If
severe, for example where the body temperature drops below
30.degree. C., hypothermia may have serious consequences such as
cardiac arrhythmias, inability of the blood to clot normally, or
interference with normal metabolism. If the period of hypothermia
is extensive, the patient may even experience impaired immune
response and increased incidence of infection.
[0005] Simple methods for treating accidental hypothermia have been
known since very early times. Such methods include wrapping the
patient in blankets, administering warm fluids by mouth, and
immersing the patient in a warm water bath. If the hypothermia is
not too severe, these methods may be effective. However, wrapping a
patient in a blanket depends on the ability of the patient's own
body to generate heat to re-warm the body. Administering warm
fluids by mouth relies on the patient's ability to swallow, and is
limited in the temperature of the liquid consumed and the amount of
fluid that may be administered in a limited period of time.
Immersing a patient in warm water is often impractical,
particularly if the patient is simultaneously undergoing surgery or
some other medical procedure.
[0006] More recently, hypothermia may be treated in a more complex
fashion. Heated warming blankets may be applied to a patient or
warming lamps that apply heat to the skin of the patient may be
used. Heat applied to the patient's skin, however, has to transmit
through the skin by conduction or radiation which may be slow and
inefficient, and the blood flow to the skin may be shut down by the
body's thermoregulatory response, and thus, even if the skin is
warmed, such mechanisms may be ineffective in providing heat to the
core of the patient's body. When breathing gases are administered
to a patient, for example a patient under anesthesia, the breathing
gases may be warmed. This provides heat relatively fast to the
patient, but the amount of heat that can be administered without
injuring the patient's lungs is very limited. An alternative method
of warming a hypothermic patient involves infusing a hot liquid
into the patient via an IV infusion, but this is limited by the
amount of liquid that can be infused and the temperature of the
liquid.
[0007] In extreme situations, a very invasive method may be
employed to control hypothermia. Shunts may be placed into the
patient to direct blood from the patient through an external
machine such as a cardiopulmonary bypass (CPB) machine which
includes a heater. In this way, the blood may be removed from the
patient, heated externally, and pumped back into the patient. Such
extreme measures have obvious advantages as to effectiveness, but
also obvious drawbacks as to invasiveness. The pumping of blood
through an external circuit that treats the blood is generally
quite damaging to the blood, and the procedure is only possible in
a hospital setting with highly trained personnel operating the
equipment.
[0008] Accidental hyperthermia may also result from various
conditions. Where the normal thermoregulatory ability of the body
is lost, because of disease or anesthesia, run-away hyperthermia,
also known as malignant hyperthermia, may result. The body may also
set a higher than normal set point resulting in fever which is a
type of hyperthermia. Like hypothermia, accidental hyperthermia is
a serious condition that may sometimes be harmful, even fatal. In
particular, hyperthermia has been found to be neurodestructive,
both in itself or in conjunction with other health problems such as
traumatic brain injury or stroke, where a body temperature in
excess of normal has been shown to result in dramatically worse
outcomes, even death.
[0009] As with hypothermia, when the condition is not too severe,
simple methods for treating the condition exist, such as cold water
baths and cooling blankets, or antipyretic drugs such as aspirin or
acetaminophen, and for the more extreme cases, more effective but
complex and invasive means such as cooled breathing gases, cold
infusions, and blood cooled during CPB also exist. These, however,
are subject to the limitations and complications as described above
in connection with hypothermia.
[0010] Although both hypothermia and hyperthermia may be harmful
and require treatment in some case, in other cases hyperthermia,
and especially hypothermia, may be therapeutic or otherwise
advantageous, and therefore may be intentionally induced. For
example, periods of cardiac arrest or cardiac insufficiency in
heart surgery result in insufficient blood to the brain and spinal
cord, and thus can produce brain damage or other nerve damage.
[0011] Hypothermia is recognized in the medical community as an
accepted neuroprotectant and therefore a patient is often kept in a
state of induced hypothermia. Hypothermia also has similar
advantageous protective ability for treating or minimizing the
adverse effects of certain neurological diseases or disorders such
as head trauma, spinal trauma and hemorrhagic or ischemic stroke.
Moreover, hypothermia has been found to be protective of the
kidneys from damage due to exposure to nephrotoxic contrast media,
such as is used during vasculature imaging methods like coronary
angiography.
[0012] For the above reasons and others, it is sometimes desirable
to induce whole-body or regional hypothermia for the purpose of
facilitating or minimizing adverse effects of certain surgical or
interventional procedures such as open heart surgery, aneurysm
repair surgeries, endovascular aneurysm repair procedures, spinal
surgeries, or other surgeries where blood flow to the brain, spinal
cord or vital organs may be interrupted or compromised. Hypothermia
has also been found to be advantageous to protect cardiac muscle
tissue after a myocardial infarct (MI).
[0013] Current methods of attempting to induce hypothermia
generally involve constant surface cooling, by cooling blanket or
by alcohol or ice water rubs. However, such cooling methods are
extremely cumbersome, and generally ineffective to cool the body's
core. The body's response to alcohol or ice water applied to the
surface is to shut down the circulation of blood through the
capillary beds, and to the surface of the body generally, and thus
to prevent the cold surface from cooling the core. If the surface
cooling works at all, it does so very slowly. There is also an
inability to precisely control the temperature of the patient by
this method. Patient safety issues may arise when, for example, ice
water baths are used in the presence of defibrillators and other
common hospital equipment.
[0014] If the patient is in a surgical setting, the patient may be
anesthetized and cooled by cardiopulmonary bypass as described
above. Generally, however, this is only available in the most
extreme situations involving a full surgical team and full surgical
suite, and importantly, is only available for a short period of
time because of the damage to the blood caused by pumping the blood
through the extracorporeal circuit comprised of pumps and tubing.
Generally surgeons do not wish to pump the blood for periods longer
than 4 hours, and in the case of stroke or traumatic brain damage,
it may be desirable to induce hypothermia for longer than a full
day. Because of the direct control of the temperature of a large
amount of blood, this method allows fairly precise control of the
patient's temperature. However, it is this very external
manipulation of large amounts of the patient's blood that makes
long term use of this procedure very undesirable.
[0015] Means for effectively adding or removing heat to or from the
core of the body that do not involve pumping the blood with an
external, mechanical pump have been suggested. For example, a
method of treating hypothermia or hyperthermia by means of a heat
exchange catheter placed in the bloodstream of a patient was
described in U.S. Pat. No. 5,486,208 to Ginsburg, the complete
disclosure of which is incorporated herein by reference. Means of
controlling the temperature of a patient by controlling such a
system is disclosed in U.S. Pat. No. 5,837,003, also to Ginsburg,
the complete disclosure of which is incorporated herein by
reference. A further system for such controlled intervascular
temperature control is disclosed in U.S. Pat. No. 6,620,188 to
Ginsburg et al., and U.S. Pat. No. 6,849,083 to Ginsburg, the
complete disclosure of which is incorporated herein by reference.
Those patents and publication disclose a method of treating or
inducing hypothermia by inserting a heat exchange catheter having a
heat exchange area including a balloon with heat exchange fins into
the bloodstream of a patient, and circulating heat exchange fluid
through the balloon while the balloon is in contact with the blood
to add or remove heat from the bloodstream. (As used herein, a
balloon is a structure that is readily inflated under pressure and
collapsed under vacuum.)
[0016] A number of catheter systems for cooling tissue adjacent the
catheter or regulating the temperature of the catheter using the
temperature of fluid circulating within the catheter are shown in
the published art. Some such catheters rely on a reservoir or
similar tank for a supply of heat exchange fluid. For example, U.S.
Pat. No. 3,425,419 to Dato, U.S. Pat. No. 5,423,811 to Imran et
al., U.S. Pat. No. 5,733,319 to Neilson, et al., and U.S. Pat. No.
6,019,783 to Phillips, et al., disclose catheters with circulating
heat exchange fluid from a tank or reservoir. For such systems that
involve a catheter placed in the bloodstream, however, difficulties
arise in sterilizing the fluid source between uses and rapidly
changing the temperature of a large volume of fluid having a
significant thermal mass.
[0017] It has been recognized that certain situations call for more
cooling power than has been available using present systems. For
example, it is postulated that reducing the time to cool a
patient's blood immediately after a stroke or coronary event may
improve the chance that the patient will recover, or at least
reduce the amount of damage done due to ischemia. One way to reduce
the time necessary to cool a patient's core body temperature to a
desired target value is to maximize the cooling power available to
remove heat from the patient's blood. However, presently available
systems, such as those described above, are limited in the cooling
power they can provide, or are too invasive as described in the
case of heat exchange with extracorporeal circulation.
[0018] For the foregoing reasons, there is a need for a rapid and
effective means to add or remove heat from the fluid supply for a
catheter used to control the body temperature of a patient in an
effective and efficient manner, while avoiding the inadequacies of
the prior art methods. Such a system would rapidly, efficiently and
controllably provide for heating or cooling the temperature of a
patient or target tissue, and regulates the temperature of the
patient or target tissue based on feedback from the temperature of
the patient or target tissue. It would be particularly advantageous
to provide a system that would reliably supply increased cooling
power compared to present systems, provide for enhanced removal of
heat from a patient's body, decrease the time necessary to reduce
the patient's body temperature to a desired target temperature, and
that may be deployed in both surgical and general wards of the
hospital by at least one operator. The present invention fulfills
this and other needs.
SUMMARY OF THE INVENTION
[0019] The present invention avoids many of the problems of the
prior art by providing an improved system to control the heating
and/or cooling of a catheter within a body. The system generally
includes a control unit exterior to body, a number of conduits
extending from the control unit, and a heat transfer catheter in
communication with the control unit via the conduits. The control
unit modulates the temperature of a heat transfer region on the
catheter using an advantageous control methodology to avoid
over-shooting a target temperature. The catheter and conduits
preferably define a fluid circulation path, wherein the control
unit modulates the temperature of the heat transfer region by
adjusting the temperature of a heat transfer fluid within the
circulation path. Desirably, the control unit defines a cavity and
the conduits are connected to a cassette that fits within the
cavity, the cassette having heat exchanger element through which
the heat exchange fluid flows.
[0020] In one aspect of the present invention, a controller for
controlling the temperature and flow of heat exchange fluid within
a circuit is provided. The circuit is of a type that includes a
heat exchange catheter, a heat exchanger, and a pump for flowing
heat exchange fluid through the circuit. The controller includes a
heat and/or cold generating element in thermal contact with the
heat exchanger containing the heat exchange fluid. A patient sensor
is positioned and configured to generate a signal representing a
biophysical condition of the patient. The microprocessor in the
controller receives the signal from the patient sensor and responds
by controlling the generating element. The control unit further
includes a mechanical drive unit for activating the pump contained
in the circuit, and a safety sensor for detecting a fluid parameter
in the circuit to generate a safety signal representative of the
presence or absence of the fluid parameter. The safety signal is
transmitted to the microprocessor that responds by controlling the
operation of the pump. The sensor may be a bubble detector, and the
fluid parameter is gas entrained in the heat exchange fluid.
Alternatively, the circuit further comprises a reservoir, and the
sensor is a fluid level detector for detecting a low fluid level in
the reservoir.
[0021] In a still further aspect of the present invention, a heat
transfer catheter flow system comprises a heat transfer medium
circulation loop including a transfer catheter, a heat exchange
element, and conduits coupled to the heat transfer catheter and
heat exchange element that enable circulation of the heat transfer
medium therebetween. The system further includes a pump head in
contact with heat transfer medium within the circulation loop for
circulating the medium through the loop. A cassette including the
heat exchange element and the pump head mates with a controller
housing a control circuit and a pump motor so that the pump head
engages the pump motor. An electronic feedback loop that detects
back-torque experienced by the pump motor provides feedback to a
control circuit that in turn controls the speed of the pump
motor.
[0022] In another aspect, the present invention provides a
controller for controlling the temperature and flow of heat
exchange fluid within a circuit of the type that has a heat
exchange catheter, a heat exchange element, and a pump for flowing
heat exchange fluid through the circuit. The controller includes a
heat and/or cold generating element in thermal contact with the
heat exchange element. A mechanical drive unit activates the pump
contained in the circuit to pump the heat exchange fluid. The
controller includes a microprocessor connected to control both the
generating element and the mechanical drive unit. A safety system
is provided for detecting problems in the circuit. The safety
system includes a plurality of sensors that generate signals
indicative of respective parameters of the system and/or patient.
The signals are transmitted to the microprocessor that responds by
controlling the operation of the generating element and the
mechanical drive unit. In one embodiment, the safety system
includes a sensor for detecting the fluid level within the circuit.
In a further embodiment, the safety system includes a sensor for
detecting the temperature of a location within the patient, and
further may include a redundant sensor for detecting the
temperature of a location within the patient wherein a
microprocessor is responsive to a difference in the two sensed
patient temperatures. Furthermore, the safety system may include
sensors for detecting bubbles within the circuit, detecting the
operating status of the generating element, or detecting the
operating status of the mechanical drive unit.
[0023] The present invention also provides a method of regulating
the temperature of patient, comprising the steps of: providing a
heat exchange catheter system including a heat exchange catheter
having a fluid path therethrough, a pair of conduits fluidly
connected to the heat exchange catheter, and a heat exchanger
connected via the conduits to circulate heat exchange medium
through the exchange catheter; providing a first controller adapted
to couple to the heat exchanger of the heat exchange catheter
system, the first controller including a heat and/or cold
generating element therein for exchanging heat at a first rate with
the heat exchange medium within the heat exchanger; providing a
second controller adapted to couple to the heat exchanger of the
heat exchange catheter system, the second controller including a
heat and/or cold generating element therein for exchanging heat at
a second rate with the heat exchange medium within the heat
exchanger; coupling the heat exchange catheter system with the
first controller; inserting the heat exchange catheter into the
patient; regulating the temperature of the patient by exchanging
heat at the first rate between the generating element of the first
controller and the heat exchanger; de-coupling the heat exchange
catheter system from the first controller; coupling the heat
exchange catheter system with the second controller; and regulating
the temperature of the patient by exchanging heat at the second
rate between the generating element of the second controller and
the heat exchanger. The first and second controller may actually be
the same physical device, but the method of coupling, decoupling,
and subsequently recoupling the device may provide benefits, for
example when the patient is being transported from one location to
another, or is undergoing a therapeutic or diagnostic procedure, as
described below.
[0024] The method may include performing a therapeutic or
diagnostic procedure on the patient between the steps of
de-coupling the heat exchange catheter system from the first
controller and the step of coupling the heat exchange catheter
system with the second controller. Indeed, the first controller and
the second controller may be the same physical device.
[0025] In a still further method of the present invention, the rate
of change of a patient's body temperature is controlled using a
heat transfer catheter and associated controller. The transfer
catheter has a heat transfer region thereon, and the controller is
placed in communication with the catheter via conduits. The
controller is adapted to elevate or depress the temperature of the
catheter heat transfer region relative to the body temperature. The
patient's body temperature within a body cavity or in another
location is sensed, while the temperature of the heat transfer
region is determined. A target temperature is then selected. The
target temperature may be different than the body temperature, or
may be the same if maintenance of normal patient temperature is the
goal. A ramp rate equal to the time rate of change of temperature
from the body temperature to the target temperature is selected.
The temperature of the transfer region of the catheter based on the
ramp rate is set. The method includes monitoring the temperature
differential between the target temperature and the body
temperature, and reducing the ramp rate when the temperature
differential reduces below a predetermined threshold. Desirably,
the heat transfer catheter and conduits defined a fluid circulation
path therethrough, wherein the step of setting the temperature of
the catheter heat transfer region comprises setting the temperature
of a circulating fluid within the circulation path. Preferably, the
step of determining the temperature of the catheter heat transfer
region comprises directly or indirectly sensing the temperature of
the circulating fluid. A comparison may be made between the target
temperature and the temperature of the circulating fluid, which is
then used to adjust the temperature of the circulating fluid.
[0026] In a further aspect, the present invention provides a system
capable of reducing the temperature of a patient in a controllable
and rapid matter. The system includes an arrangement of heat
exchangers, pumps and cooling media that is capable of removing
sufficient heat energy so as to be able to maintain the temperature
of a primary coolant loop in the range of 0-5 degrees centigrade,
even when heat loads are in the range of about 400 to about 550
watts.
[0027] In yet another aspect, the present invention includes a
system for adjusting the temperature of a patient, comprising: a
primary fluid circuit, the circuit including a primary fluid
reservoir, a primary fluid circuit pump, a heater cooler, primary
fluid circuit lines connecting the primary fluid circuit pump to
the primary fluid reservoir to the heater/cooler such that a
continuous flow path for circulating primary fluid from the
reservoir to the heater/cooler and back to the primary fluid
reservoir is formed; access points in the primary fluid circuit,
the access points fluidly connecting the primary fluid circuit to a
primary fluid circuit side of a heat exchanger, the heat exchanger
also having a secondary fluid circuit side; a heat exchange
catheter insertable within a patient, the catheter configured to
increase, decrease or maintain the temperature of the patient; a
secondary fluid circuit for flowing secondary fluid through the
secondary circuit side of the heat exchanger and the heat exchange
catheter, the secondary fluid circuit including a secondary fluid
reservoir, and a secondary fluid circuit pump for flowing a
secondary heat exchange fluid from the secondary fluid reservoir
through secondary fluid circuit to the heat exchange catheter and
back through the secondary fluid circuit to the secondary fluid
reservoir; at least one fluid sensor configured to provide a signal
representative of a temperature of the primary or secondary fluid
circuit; a patient sensor configured to provide a signal
representative of a temperature of the patient; and a controller
configured to receive the signals from the patient sensor and the
primary fluid sensor and being responsive to the signals to control
the heater/cooler to adjust the temperature of the fluid flowing
within the fluid circuits. In yet another aspect, the volume of the
primary fluid pathway or circuit increases when the heat exchanger
is connected with the primary fluid pathway or circuit.
[0028] In a further aspect, the present invention includes the case
wherein the controller includes a microprocessor configured to be
responsive to sensors and to provide control signals as needed to
control the operation of the system.
[0029] In a still further aspect, the present invention includes a
power supply for supplying power to the system, including the
heater/cooler; controller circuitry for controlling the operation
of the system, the controller circuitry including means for
determining if the power supply is operative and operating within
parameters determined to be appropriate, means for monitoring the
operation of the system, means for determining an error state of
the monitored system, and means for alerting an operator of the
presence of an error state.
[0030] In yet another aspect, the present invention includes the
cases wherein the controller controls the heater/cooler to drive
the temperature of the fluid in the primary fluid circuit towards a
predetermined temperature prior to fluidly connecting the heat
exchanger to the primary fluid circuit and wherein the controller
controls the heater/cooler to drive the temperature of the fluid in
the primary fluid circuit towards a predetermined temperature prior
to initiation of treatment of a patient.
[0031] In a still further aspect of the present invention, the
primary fluid circuit includes temperature sensors disposed in the
primary fluid circuit, the temperature sensors providing signals
representative of the temperature of the primary fluid passing
through the access points flowing into and out of the primary fluid
circuit side of the heat exchanger. Alternatively, the temperature
difference between the fluid flowing into and out of the primary
fluid circuit side of the heat exchanger is proportional to the
heat exchange being delivered to the secondary fluid circuit, and
is representative of the heat exchange being delivered to the
patient. In yet another alternative aspect, the controller is
responsive to the signals provided by the temperature sensors to
determine the difference in the temperature of the primary fluid
flowing into and out of the access points, and to provide an alert
if the determined difference is indicative of a problem condition,
or the controller is responsive to the signals provided by the
temperature sensors to provide an alert if the signals are
indicative of a problem condition.
[0032] In another aspect of the present invention, the secondary
fluid reservoir includes an air trap disposed between an inlet to
the reservoir and the secondary fluid circuit pump. In one aspect
the air trap is a semi-permeable member permitting at least a
portion of the secondary fluid to flow through the semi-permeable
member and in another aspect the air trap is formed from foam.
[0033] In yet another aspect of the present invention, the
secondary fluid circuit contains a particulate filter. In one
aspect, the particulate filter is a semi-permeable member
permitting at least a portion of the secondary fluid to flow
through the semi-permeable member and in another aspect the
particulate filter is formed from foam for formed from a
screen.
[0034] In a further aspect, the present invention also includes a
level detector disposed in the secondary fluid circuit to detect a
level of the fluid within the secondary fluid circuit, the level
detector providing a signal representative of the level of fluid in
the secondary fluid circuit to the controller. In one aspect, the
level detector is disposed in cooperation with the secondary fluid
reservoir to detect a level of the fluid within the secondary fluid
reservoir.
[0035] In yet another aspect of the present invention, the level
detector may be a bubble detector or an air in line detector.
[0036] In yet another aspect of the present invention, the
controller sends a start signal to the secondary fluid pump in
response to a signal from the level detector representative of a
predetermined fluid level. Alternatively, the controller may send a
stop signal to the secondary fluid pump in response to a signal
from the level detector representative of a predetermined low fluid
level.
[0037] In one aspect of the present invention, the secondary fluid
circuit pump and secondary fluid reservoir and heat exchanger are
included in a cassette configuration that is provided to the
operator in a sterile condition. In a further aspect, the present
invention also includes a reusable housing in which are disposed
the primary fluid reservoir, primary fluid circuit pump,
microprocessor and a secondary fluid circuit pump motor, the
housing being configured to removably receive the cassette such
that the secondary fluid circuit pump releasably engages the
secondary fluid circuit pump motor.
[0038] In yet another aspect of the present invention, the access
points include releasable couplers for releasably coupling the heat
exchanger to the primary fluid circuit. In one aspect, the
releasable couplers fluidly seal when not connected to the primary
fluid circuit to minimize primary fluid loss from the primary fluid
circuit side of the heat exchanger and the primary fluid
circuit.
[0039] In another aspect, the present invention includes a quick
connect coupler configured to allow electrical connection of a
sensor line to a controller at about the same time the releasable
couplers of the heat exchanger are engaged. This provides for
easier and more rapid setup of the heat exchanger, which is
advantageous during an emergency situation. This arrangement also
prevents errors that may occur if a care-giver neglects to connect
the sensor line before start up of the system.
[0040] In still another aspect of the present invention, the
primary fluid circuit further comprises a check valve for
controlling a fluid pressure within the primary fluid circuit such
that the fluid pressure does not exceed a predetermined value. In
yet another aspect, the cassette and catheter may be disconnected
from the primary fluid circuit and connected to a different primary
circuit without compromising sterility or fluid isolation of the
secondary fluid circuit of the cassette and catheter.
[0041] In another aspect of the present invention, the fan/blower
output of the heater/cooler is reduced when the controller
determines that a sensed temperature is within a predetermined
range. In another aspect, the fan/blower output of the
heater/cooler is reduced when the controller determines that the
sensed temperature is within a predetermined range for a
predetermined amount of time. In still another aspect, an output of
the primary and/or secondary fluid pump is reduced when the
controller determines that a sensed temperature is within a
predetermined range. In a still further aspect, the output of the
primary and/or secondary pump is reduced when the controller
determines that demand for patient temperature change is
reduced.
[0042] In yet another aspect of the present invention, the primary
fluid circuit is configured such that the majority of volume of
primary fluid contained with the heat exchanger is recovered to the
primary fluid reservoir prior to disconnection of the heat
exchanger from the primary fluid circuit.
[0043] In another aspect of the present invention, the heat
exchanger is provided to the operator with the primary fluid side
pre-filled with primary fluid. In still another aspect, the heat
exchanger is provided to the operator with the secondary fluid side
pre-filled with secondary fluid.
[0044] In one aspect of the present invention the heat exchanger
when connected is maintained in electrical isolation from the
heater/cooler and electrical inputs to components of the primary
fluid loop.
[0045] In another aspect of the present invention, the primary
fluid circuit includes a means for maintaining the electrical
conductivity at a value below a predetermined value. In another
aspect of the present invention, the means includes a sensor
configured to sense an electrical characteristic of the fluid
within the fluid circuit.
[0046] In still another aspect, the present invention includes a
priming fluid circuit for providing secondary heat exchange fluid
to the secondary fluid circuit. In a further aspect, the priming
fluid circuit includes a prime line and a vent line, at least of
one of the prime line and vent line having a valve, and at least
one sensor for determining when the secondary circuit is
sufficiently filled with fluid. In a further aspect, at least one
of the valves in the prime line and vent line is a clamp that
engages the line to obstruct fluid flow in the line. In yet another
aspect, the at least one of the valves in the prime line and vent
line are controlled by the controller to initiate and complete
filling the secondary fluid circuit with secondary fluid.
[0047] In another aspect of the present invention, the access
points are configured to receive primary circuit fluid to fill the
primary fluid reservoir. Still further, at least one of the fluid
lines is engaged with the at least one of the fluid lines of the
cassette when the cassette is removably received by the
housing.
[0048] In still another aspect of the present invention, the
controller controls the temperature of the primary fluid circuit at
a level sufficient to prevent freezing of the secondary fluid in
the secondary fluid circuit.
[0049] In yet another aspect of the present invention the, heat
exchanger includes a pair of intermediate fluid pathways. The two
intermediate pathways, a primary intermediate pathway and a
secondary intermediate fluid pathway, are physically separated from
each other, but are in thermal communication with each other. This
provides for the exchange of heat energy between the intermediate
fluid pathways, while preventing the possibility of contaminating
the secondary heat exchange fluid which may flow into a patient
with primary circuit fluid, which may or may not be biocompatible.
In a further aspect, the physical separation of the intermediate
fluid pathways ensures that the primary fluid circuit will not be
contaminated should the secondary fluid circuit be invaded by blood
or other bodily fluids. In still another aspect, the intermediate
fluid pathways, when connected to their respective primary or
secondary fluid circuits, increase the volume of these
circuits.
[0050] Other features and advantages of the invention will become
apparent from the following detailed description, taken in
conjunction with the accompanying drawings, which illustrate, by
way of example, the features of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] FIG. 1 is a perspective view of a patient undergoing
treatment using a system in accordance with the present
invention;
[0052] FIG. 2 is a schematic illustration of a disposable heat
exchange cassette attached to a heat exchange catheter and an
external fluid source, and positioned for insertion into a suitable
opening in a re-usable control unit of the present invention,
[0053] FIGS. 3A-3B together show a flowchart of a control scheme of
the heat exchange system of the present invention;
[0054] FIG. 4 is a graph of the sensed temperature of a target
tissue or body fluid over time under the influence of the control
scheme of FIGS. 3A-3B;
[0055] FIG. 5A is a perspective view of an exemplary re-usable
control unit of the present invention;
[0056] FIG. 5B is a perspective view of an upper portion of the
control unit of FIG. 5A;
[0057] FIG. 5C is a plan view of an exemplary control panel for the
control unit of FIG. 5A;
[0058] FIG. 6 is a schematic view of an embodiment of the system of
the present invention showing a heat exchanger in fluid
communication with a positive pressure side of a primary fluid
circuit pump;
[0059] FIG. 7 is a schematic view of another embodiment of the
system of the present invention showing the heat exchanger in fluid
communication with a negative pressure side of the primary fluid
circuit pump;
[0060] FIG. 8 is a schematic diagram of exemplary components of the
present invention, illustrating communication and feedback
interconnections therebetween;
[0061] FIG. 9 is an exploded view of an embodiment of the heat
exchange cassette of the present invention;
[0062] FIG. 10 is a perspective view of the embodiment of FIG.
9;
[0063] FIG. 10A is an enlarged perspective view of a portion of the
embodiment of FIG. 10;
[0064] FIG. 11A is an exploded perspective view of a cassette
portion of the embodiment of FIG. 9 showing an exterior view of the
cassette portion;
[0065] FIG. 11B is an exploded perspective view of the cassette
portion of the embodiment of FIG. 9 showing a view of the internal
structure of the cassette portion;
[0066] FIG. 12 is a graphical illustration of the heat extraction
(power) capability of one embodiment of the present invention as a
function of primary fluid temperature;
[0067] FIG. 13 is a graphical comparison of the temperature
reducing capability of an embodiment of the present invention
compared to the temperature reducing capability of a prior
system.
DETAILED DESCRIPTION OF THE INVENTION
[0068] The present invention is primarily intended to include a
catheter placed in the bloodstream of a patient for regulating the
patient's body temperature, although those of skill in the art will
understand that various other applications for the system of the
present invention are possible. Indeed, the present invention may
have applications beyond controlling the temperature of an internal
body fluid, and the claims should not be so limited. In a preferred
application, one or more of the heat exchange catheters of the
present invention are positioned within a patient's vasculature to
exchange heat with the blood in order to regulate the overall body
temperature, or to regulate the temperature of a localized region
of the patient's body. Heat exchange fluid is then circulated
through the catheter to exchange heat between the blood and the
heat exchange fluid, and a controller manages the functioning of
the system. The catheters may be, for example, suitable for
exchanging heat with arterial blood flowing toward the brain to
cool the brain, and may thus prevent damage to brain tissue that
might otherwise result from a stroke or other injury, or cooling
venous blood flowing toward the heart to cool the myocardium to
prevent tissue injury that might otherwise occur following an MI or
other similar event.
[0069] In general, the invention provides a preferred control unit
and method for controlling the temperature and flow of heat
transfer fluid for a heat transfer catheter used for controlling
the body temperature of a patient. The control unit initially
automatically supplies heat transfer fluid to the heat transfer
catheter to prime the heat exchange catheter for use. It also
receives input from the user, receives temperature information from
sensors that sense patient temperature information, and based
thereon, automatically controls the temperature and flow of the
heat transfer fluid. Further, based on feedback from a pump in a
cassette containing the heat transfer fluid, the control unit
supplies heat transfer fluid at a relatively constant pressure. The
cassette and the controller, working together, have several warning
or alarm states that alert the user of potentially hazardous
situations, for example, by shutting down the pump motor and
notifying the user if the fluid level in the cassette is
unacceptably low.
Overview of Heat Exchange System
[0070] Any suitable heat exchange catheter may be utilized in a
heat exchange system for regulating the temperature of a patient or
a region of the patient's body and controlled by the control unit
as disclosed herein. In addition to the catheters disclosed herein,
and by way of illustration and not of limitation, catheters that
may be utilized in this invention are the catheters disclosed in
U.S. Pat. No. 5,486,208 to Ginsburg, U.S. Pat. No. 5,837,003 to
Ginsburg, U.S. Pat. No. 6,610,083 to Keller et al., U.S. Pat. No.
6,702,840 to Keller et al., U.S. Pat. No. 6,752,786 to Callister,
U.S. Pat. No. 6,620,188 to Ginsburg et al., U.S. Pat. No. 6,849,083
to Ginsburg, U.S. Pat. No. 5,624,392 to Saab, and U.S. Pat. No.
6,440,158 to Saab, the complete disclosure of each of which is
hereby incorporated in full herein by reference. It will be
understood by those skilled in the art that for the purposes of
providing heat exchange with a patient at the rates possible using
the various embodiments of the present invention, a catheter with
sufficient heat exchange power must be employed.
[0071] While the various embodiments of the system and method of
the present invention will be described with reference to providing
a source of cooling or heating fluid for circulation within a
catheter, those skilled in the art will understand that the fluid
may also be circulated through other devices designed to alter the
temperature of a patient. For example, instead of a catheter, the
fluid may be circulated through a heating or cooling pad or blanket
designed to be used externally to a patient.
[0072] One example of such a heat exchange catheter system 20 is
shown in FIG. 1, and includes a control unit 22 and a heat exchange
catheter 24 formed with at least one heat transfer section 44. The
heat transfer section or sections are located on that portion of
the catheter 24, as illustrated by section 26, that is inserted
into the patient. This insertion portion is less than the
full-length of the catheter and extends from the location on the
catheter just inside the patient, when the catheter is fully
inserted, to the distal end of the catheter. The control unit 22
may include a fluid pump 28 for circulating a heat exchange fluid
or medium within the catheter 24, and a heat exchanger component
for heating and/or cooling circulating fluids within the heat
transfer system 20. A reservoir or fluid bag 30 may be connected to
the control unit 22 to provide a source of heat transfer fluid such
as, saline, blood substitute solution, or other biocompatible
fluid. A circulatory heat exchange flow channel within the catheter
may be respectively connected to inlet 32 and outlet 34 conduits of
the pump 28 for circulation of the heat transfer fluid through the
balloon to cool the flow of body fluid such as blood within a
selected body region. A similar arrangement may be implemented for
heating of selected body regions simultaneously or independently of
each other using the cooling component of the system.
[0073] The control unit 22 may further receive data from a variety
of sensors which may be, for example, solid-state thermocouples to
provide feedback from the catheter and various sensors to provide
patient temperature information representing core temperature or
temperature of selected organs or portions of the body. For
instance, sensors may include a temperature probe 36 for the brain
or head region, a rectal temperature probe 38, an ear temperature
probe 40, an esophageal temperature probe (not shown), a bladder
temperature probe (not shown), and the like. Alternatively, a
temperature probe may be placed in a patient's blood vessel at a
location adjacent the heat transfer balloon. In yet another
embodiment, the temperature probe may be placed in the blood stream
distal of the heat transfer balloon.
[0074] Based upon sensed temperatures and conditions, the control
unit 22 may direct the heating or cooling of the catheter in
response. The control unit 22 may activate a heat exchanger at a
first sensed temperature to heat fluid which is then circulated
through the balloon, and may also de-activate the heat exchanger at
a second sensed temperature which may be relatively higher or lower
than the first sensed temperature or any other predetermined
temperature. Alternatively, the control unit may actively cool the
heat exchange fluid to cool the balloon. The control unit 22 may
operate multiple heat transfer units to independently heat or cool
different selected heat transfer sections to attain desired or
preselected temperatures in body regions. Likewise, the controller
22 may activate more than one heat exchanger to control temperature
at particular regions of the patient's body. The controller might
also activate or de-activate other apparatus, for example external
heating blankets or the like, in response to sensed
temperatures.
[0075] The regulation exercised over the heat transfer catheters or
other devices may be a simple on-off control, or may be a
significantly more sophisticated control scheme including
regulating the degree of heating or cooling, ramp rates of heating
or cooling, proportional/integral/derivative (PID) or nonlinear
control as the temperature of the heat exchange region or patient
approaches a target temperature, or the like.
[0076] The control unit 22 may further include a thermoelectric
cooler and heater (and associated flow conduits) that are
selectively activated to perform both heating and cooling functions
with the same or different heat transfer mediums within the
closed-loop catheter system. For example, a first heat transfer
section 42 located on the insertion portion 26 of at least one
temperature regulating catheter 24 may circulate a cold solution in
the immediate head region, or alternatively, within a carotid
artery or other blood vessel leading to the brain. The head
temperature may be locally monitored with temperature sensors 36
positioned in a relatively proximate exterior surface of the
patient or within selected body regions. Another heat transfer
section 44 of the catheter 24 also located on the insertion portion
26 may circulate a heated solution within a collapsible balloon or
otherwise provide heat to other body locations through heat
elements or other mechanisms described in accordance with other
aspects of the invention. While heat exchange catheter 24 may
provide regional hypothermia to the brain region for
neuroprotective benefits, other parts of the body may be kept
relatively warm so that adverse side effects such as discomfort,
shivering, blood coagulopathies, immune deficiencies, and the like,
may be avoided or minimized. Warming of the body generally below
the neck may be further achieved by insulating or wrapping the
lower body in a heating pad or blanket 46 while the head region
above the neck is cool. It should be understood of course that
multiple heat exchange sections of the catheter 24 may be modified
to provide whole body cooling or warming to affect body core
temperature.
Exemplary Heat Exchange System
[0077] The present invention contemplates the use of a re-usable
controller or control console having a heater/cooler device therein
and which receives a disposable heat exchange element coupled via
conduits to a distal in-dwelling heat exchange catheter. More
specifically, the controller desirably includes an outer housing
having an opening or slot for receiving the heat exchange element,
the opening and housing ensuring reliable positioning of the heat
exchange element in proximity with the heater/cooler device. In
this manner, set up of the system is facilitated because the
operator only needs to fully insert and seat the heat exchange
element into the controller opening in order to couple the reusable
and disposable portions of the system.
[0078] In an exemplary embodiment, FIG. 2 illustrates a heat
exchange catheter system that includes a re-usable control unit 50
and a plurality of disposable components including a heat exchange
catheter 52, a heat exchange cassette 54, a saline bag 56, and a
plurality of fluid flow conduits including a two-way conduit 74
extending distally from the heat exchange cassette 54. The
re-usable control unit 50 includes an outer housing 64 within which
is provided a heater/cooler, a primary fluid circuit reservoir, a
primary fluid circuit pump, a controller processor and various
control cables and temperature, pump and flow controls, all not
shown. Within control unit 50 is also a pump drive motor 68 which
drives a secondary fluid circuit pump disposed within heat exchange
cassette 54 through a solenoid driven engagement swing arm and
coupling (not shown), an optical beam source 93 and optical beam
sensor 94 which may be used to determine a fluid level within the
heat exchange cassette 54. In addition, a manual input unit (not
shown) utilizing a graphical user interface enables an operator to
enter desirable operating parameters of the controller, for example
a preselected temperature for the brain. Each of the electronic
devices provided within the control unit 50 communicate through
suitable wiring. The heat exchange cassette 54 is in fluid
communication with the primary fluid circuit through primary
circuit fluid conduits or access points 67, 69, thus forming a
closed fluid circuit comprising the primary fluid circuit
reservoir, primary fluid circuit pump and heat exchange cassette
54.
[0079] The heat exchange catheter 52 is formed with a catheter
conduit 74 and a heat exchanger 76 which may be, for example, a
heat exchange balloon operated using a closed-loop flow of a
biocompatible fluid that serves as the heat exchange medium. The
catheter 52 may include a working lumen (not shown) for injection
of drugs, fluoroscopic dye, or the like, and for receipt of a
guidewire 78 for use in placing the catheter at an appropriate
location in the patient's body. A sensor 80 may be provided on the
catheter 52 distal to the heat exchanger 76 to monitor the
temperature of the heat exchange balloon, and other sensors (not
shown) may be provided as desired to monitor the blood temperature
at the distal tip of the catheter, at the proximal tip of the
balloon, or at any other desired location along the catheter.
[0080] The heat exchange cassette 54 includes a heat exchanger 96
and a fluid reservoir compartment that houses a secondary fluid
circuit pump. In a preferred embodiment, the secondary fluid
circuit is a closed system physically isolated from the primary
fluid circuit by heat exchanger 96 but with the secondary fluid
circuit and the primary fluid circuit in heat exchange
communication through the heat exchanger. This arrangement is
advantageous in that different fluids may be used in the primary
fluid circuit that are not necessarily biocompatible so as to
maximize the efficiency of the heat exchanger 96 during heating or
cooling of a patient.
[0081] As seen in FIG. 2, the proximal end of the catheter conduit
74 may be connected to a multi-arm adapter 82 for providing
separate access to various channels in the catheter 52. For
example, a first arm 84 may provide access to the working lumen of
the catheter 52 for insertion of the guidewire 78 to steer the heat
exchange catheter to the desired location. First arm 84 may also be
used to provide access to the blood stream for a temperature probe
to monitor the blood temperature for control input.
[0082] Where the heat exchanger 76 is a heat exchange balloon for
closed-loop flow of secondary fluid, the adapter 82 may contain a
second arm 86 connected to an inflow line 88, and a third arm 90
connected to an outflow line 92. The inflow line 88 and outflow
line 92 are therefore placed in flow communication with respective
inflow and outflow channels (not shown) provided in the conduit 74
and heat exchanger 96. In this regard, the inflow and outflow lines
88, 92 may come together to form the dual channel conduit 62
connected to the heat exchange cassette 54.
[0083] A vent tube 61 including a valve 63 may be used to assist in
priming the secondary fluid circuit. Furthermore, an external
biocompatible fluid source such as the saline bag 56 may be placed
in fluid communication with the secondary fluid circuit using
suitable connecters. As will be explained further below, the
external fluid source 56 is used to prime the secondary fluid
circuit, including the closed-loop heat exchange balloon
system.
[0084] Still with reference to FIG. 2, and as described above, the
heat exchange cassette 54 depicted in this embodiment desirably
includes the heat exchanger 96 and a fluid reservoir compartment
98, which also holds the secondary fluid pump. The secondary fluid
circuit pump in the reservoir compartment 98 pumps heat exchange
fluid through the secondary fluid circuit through the heat
exchanger 96, and through the associated conduits and catheter 52.
As mentioned, the heat exchange cassette 54 is configured to
install into the control unit 50. In this regard, the heat exchange
cassette 54 is desirably sized to fit through an elongate slot 102
in the control unit housing 64. Once inserted, the cassette 54 is
placed in proximity to and engaged with the pump drive motor 68.
The heat exchanger 96 is connected to the primary fluid circuit
using inflow and outflow conduits, or access points, 67, 69.
[0085] When the heat exchanger cassette 54 is properly installed in
the control unit 50, the heater/cooler may act to heat or cool the
primary heat exchange fluid as that fluid is circulated through in
heat exchange contact with the secondary fluid in heat exchanger
96. The secondary fluid, which is either being heated, cooled or
maintained by the heat exchange contact with the primary fluid in
the heat exchanger 96, is pumped through the conduits leading to
the in-dwelling heat exchanger 76. When the heat exchange fluid is
circulated through the heat exchanger 76 located in the patient's
body, it may act to add or remove heat from the body. In this way,
the control unit 50 regulates the blood temperature of the patient
as desired.
[0086] A solid-state thermoelectric heater/cooler may be used to
heat or cool the primary circuit fluid, and such use is
advantageous because the same unit is capable of either generating
heat or removing heat by simply changing the polarity of the
current activating the unit. Therefore, the heater/cooler may be
conveniently controlled so as to supply or remove heat from the
system without the need for two separate units and without exchange
of the heat exchange cassette or catheter. In another embodiment, a
variable speed vapor compressor/heat pump could also be used as the
heater/cooler. Alternatively, a resistive heater could be used in
combination with a variable or constant speed compressive
cooler.
[0087] The heater/cooler and the pump drive motor 68 are responsive
to the controller processor, which receives data input through
electrical connections to numerous sensors, for example body
temperature sensors positioned to sense the temperature at various
locations within the patient. For example, the temperature may be
sensed at the patient's ear, brain region, bladder, rectum,
esophagus, or other appropriate location as desired by the
operator. Also, as mentioned, a sensor 80 may monitor the
temperature at a location distal of the heat exchanger 76, and
other sensors along the catheter 52 may provide input to the
controller processor. Additionally, the manual input unit allows an
operator to provide operating parameters to the control system such
as, for example, a pre-selected temperature for the brain and/or
the whole body of the patient. The operator input parameters are
communicated to the controller processor by means of appropriate
wiring.
[0088] The controller processor coordinates the various data
received and selectively actuates the several operational
subsystems to achieve and maintain desired results; i.e., proper
regulation of the patient's body temperature. For example, the
processor may actuate the heater/cooler to increase the amount of
heat it is removing if the actual temperature is above the
specified temperature, or it may decrease the amount of heat being
removed if the temperature is below the specified temperature.
Alternatively, the processor may slow or stop the pumping of the
primary or secondary, or both, heat exchange fluids when the sensed
body or regional temperature reaches the desired temperature.
[0089] In operation, the heater/cooler warms or chills the fluid in
the primary fluid circuit in response to temperature signals
received from the temperature sensors described above to alter the
temperature of the patient's body, or a portion of the patient's
body, as desired. The changes in temperature of the primary fluid
circuit is transferred to the fluid circulating in the secondary
fluid circuit using the heat exchanger 96, in a manner that is well
known to those skilled in the art. Thus, the heater/cooler is used
to indirectly affect the temperature of the patient, or a portion
of the patient by heating or cooling the fluid circulating in the
secondary fluid circuit.
[0090] Referring still to FIG. 2, the heat exchange cassette 54 of
this embodiment is shown as being attached to a heat exchange
catheter 52, external fluid source 56 is positioned in cooperation
with a suitable reusable control unit 50. Prior to commencing
treatment, the heat-exchange unit 54 is inserted into the reusable
control unit 50, the external fluid source 56 is attached to the
fill port and the pump 68 is automatically or passively primed and
the disposable system filled, after which the catheter is ready for
insertion in-the vasculature of the patient, for example in the
inferior vena cava or the carotid artery. Chilled or warmed
biocompatible fluid such as, for example, saline filling the
secondary circuit, is pumped into the closed circuit catheter,
which exchanges heat directly with the patient's blood. The control
unit serves to automatically-control the patient's temperature.
Once treatment with the catheter is complete, the catheter is
removed from the patient and the cassette is removed from the
reusable control unit. Both the catheter and cassette may then be
discarded. The reusable control unit, however, which never comes
into direct contact with the secondary heat exchange fluid, is
ready for immediate use for treatment on other patients, along with
a new cassette and catheter and fresh external fluid source.
Alternatively, the heat exchanger 96 may be separated from the
cassette 54, cleaned and sterilized, while the cassette is
discarded. In yet a further alternative, the entire heat exchange
cassette 54 may be suitably reconditioned for use with another
patient.
Exemplary Method of Temperature Control
[0091] The flowchart seen in FIGS. 3A and 3B illustrates an
exemplary sequence of steps that the controller processor of the
system coordinates during temperature regulation of a patient.
First, in step 110, a target temperature for the target tissue
(which may be the entire body) is selected, generally by user
input. The target temperature may be different than the body
temperature, or may be the same if maintenance of normal patient
temperature is the goal. Steps 112a and 112b involve determination
of an upper variance set point and a lower variance set point,
respectively. This is generally a pre-set buffer range above and
below the target temperature that is built or programmed into the
controller processor. These variance set points straddle the target
temperature and create a buffer range of temperature within which
the controller operates.
[0092] More specifically, the sensed temperature for the target
tissue is obtained in step 114 prior to or after step 116 in which
a heat exchanger capable of either heating or cooling body fluid is
placed in proximity with body fluid that subsequently flows to the
target tissue. Based on user input, or on a comparison between the
target temperature and the sensed tissue temperature, a
determination is made in step 118 as to whether the heat exchanger
will be operating a cooling mode, a heat mode, or a maintaining
mode. That is, if the target temperature equals the tissue
temperature then there will be no need to initially heat or cool
the body fluid and the control unit will control the heat exchanger
to maintain the tissue or blood temperature at the target
temperature.
[0093] The determination step 118 leads to three different modes of
operation of the system, depending on whether the system will be
COOLING, HEATING, or OFF. These modes of operation correspond to
steps 120a, 120b, and 120c, which appear on both the FIGS. 3A and
3B.
[0094] If the system is in the COOLING mode, the flowchart logic
leads to step 120a which compares the sensed tissue temperature
with the pre-selected target temperature. If the tissue temperature
is greater than the target temperature, the system continues
cooling as indicated in step 122, and the processor returns to
decision step 118. On the other hand, if the sensed tissue
temperature is equal to or less than the target temperature, the
heat exchanger is converted to the OFF mode as indicated in step
124 and the processor returns to decision step 118.
[0095] If the system is in the HEATING mode, the flowchart logic
leads to step 120b which also compares the sensed tissue
temperature with the pre-selected target temperature. If the tissue
temperature is less than the target temperature, the system
continues heating as indicated in step 126, and the processor
returns to decision step 118. On the other hand, if the tissue
temperature is equal to or greater than the target temperature, the
heat exchanger is converted to the OFF mode as indicated in step
128, and the processor returns to decision step 118.
[0096] If the system is in the OFF mode, the flowchart logic leads
to step 120c which compares the sensed tissue temperature with the
upper variance temperature set point. Then, if the sensed tissue
temperature is equal to or greater than the upper variance set
point, the system is converted to the COOLING mode as indicated in
step 130, and the processor returns to decision step 118. If the
tissue temperature is less than the upper variance set point, the
processor continues to step 132 in the flowchart logic, and
determines if the tissue temperature is equal to or less than the
lower variance set point, whereby the system is converted to the
HEATING mode and processor returns to decision step 118. Finally,
if the tissue temperature is between the upper and lower variance
set points, the system does nothing as indicated in step 134, and
the processor returns to decision step 118.
[0097] FIG. 4 is a graphical illustration plotting the fluctuating
sensed tissue temperature over a period of time relative to the
target temperature and variance set points. In the example, the
target temperature is set at 31 degrees Celsius, with the upper and
lower variance set points 1/2 degrees on either side. Initially,
the sensed tissue temperature is greater than the target
temperature, such as if the heat exchange catheter is placed in
contact with blood at 37 degrees Celsius. The system is first
placed in the COOLING mode so that the sensed tissue temperature is
reduced until it equals the target temperature at 136,
corresponding to steps 120a and 124 in FIG. 3A. In step 124, the
heat exchanger is converted to the OFF mode, which results in the
sensed tissue temperature climbing until it reaches the upper
variance set point at 138, corresponding to step 130 in FIG. 3B, at
which time the system begins cooling again. This cycle is repeated
in the region indicated at A.
[0098] Eventually, the patient may be unable to maintain even the
target temperature as shown by the temperature profile in the
region indicated at B. For example, after the sensed tissue
temperature reaches the target temperature at 140, and the heat
exchanger is turned OFF, the sensed target temperature may continue
to drift lower until it reaches the lower variance set point at
142. The controller logic senses this in step 132 of FIG. 3B, and
converts the system to the HEATING mode. Subsequently, the sensed
tissue temperature climbs to the target temperature at 144, and the
system is again turned OFF, corresponding to steps 120b and 128 in
FIG. 3B. Alternatively, depending on the patient and the situation,
it may be that after the sensed tissue temperature reaches the
target temperature and the heat exchanger is turned OFF, the
patient's temperature may begin to increase until it rises to the
upper variance set point temperature, at which point, as described
in box 130 the heat exchanger begins to COOL. As can be
appreciated, the sensed tissue temperature continues to fluctuate
between the upper and lower variance set points in this manner.
[0099] The control scheme as applied to the system of the present
invention has the advantage of allowing the operator to essentially
input a desired temperature after which time the system will
automatically regulate the tissue temperature until it reaches the
target temperature, and will maintain the tissue temperature at
that target temperature. The buffer range created by the upper and
lower variance set points prevents the controller from turning the
heater/cooler on and off or activating and de-activating the
primary or secondary pumps in rapid succession, actions that would
be potentially damaging to these electric devices. Moreover, the
variance points, and other parameters used by the controller to
regulate the cooling or heating power of the heater/cooler can be
varied by the operator during the course of treatment to change the
selected patient temperature or the ramp of the heating or cooling
as needed to address specific therapeutic situations. A more
sophisticated control scheme, such as the PID scheme described
below, may also be employed.
Exemplary Control Unit
[0100] FIGS. 5A-5C are various views of an exemplary heat exchange
control unit 150 of the present invention that is particularly
suited for rapid temperature regulation of a patient.
[0101] As seen in the Figures, the control unit 150 comprises a
vertically-oriented outer housing having a lower portion 152 and
upper portion 154 separated at a generally horizontal dividing line
156 located close to the top of the unit. The control unit 150 is
mounted on wheels 158 for ease of portability, with the wheels
preferably being of the swivel type having foot-actuated locks. For
ease of servicing, the upper and lower portions may be joined
together with hinges 155 at the back so that the top portion may be
lifted up and rotated back to expose the interior of the unit. In
an exemplary embodiment, the control unit 150 has a height that
enables an operator to easily access an upper control panel 160
without the need for significant bending. For example, the control
unit 150 may have a total height of between approximately 2-3 feet,
and preferably about 32 inches. The substantially horizontal
cross-section of a majority of the control unit 150 may have widths
of between one and two feet, although the lower portion 152
preferably widens at its lower end with the wheels 158 mounted on
the lower corners to provide greater stability.
[0102] FIG. 5A illustrates the front and right sides of the unit
150 wherein the control panel 160 is visible on an angled upper
panel 162 of the upper portion 154 front side. The angled upper
panel 162 also defines a fluid container receiving cavity 164
adjacent the control panel 160. Further, a plurality of handles 166
may be provided to help maneuver the control unit 150.
[0103] A heat exchange cassette-receiving opening 168 is also
provided on a front panel 169 of the control unit 150, just below
the horizontal dividing line 156. As will be explained below, the
opening 168 is sized and shaped to receive a cassette of the
present invention, analogous to the heat exchange
cassette-receiving opening 102 shown in FIG. 2. Likewise, the
control unit 150 provides all of the features that were described
above for the control unit 50 of FIG. 2, including equipment for
heating or cooling the fluid in the cassette, a pump driver, a
controller processor/microprocessor, and a manual input unit,
namely the control panel 160.
[0104] Also shown in FIG. 5A are access points 165, 167. These
access points are used to fluidly connect the heat exchanger to the
primary fluid circuit. Access points may be configured as flexible
tubing which is terminated by quick connect couplings that allow
for rapid attachment and detachment of the access points from the
cassette. The couplings may also be configured to seal upon
disconnect, thus preventing loss of primary fluid from the primary
fluid circuit. Additionally, the corresponding quick connect
couplings disposed on the cassette may also be configured to
prevent loss of primary fluid from the primary fluid side of heat
exchanger in the cassette when the access points are detached.
Alternatively, the quick connect couplings may be configured such
that insertion of the cassette into the slot 168 causes quick
connect fittings disposed on the cassette to automatically engage
and fluidly couple with quick connect fittings within the housing
to complete the fluid pathway of the primary fluid circuit so that
primary fluid may be circulated through the primary fluid side of
the heat exchanger in the cassette.
[0105] Because of the relatively high capacity for heating and
cooling, the lower portion 152 of the control unit housing includes
a plurality of vents 170 to facilitate convective heat exchange
between the interior of the housing and the surrounding environment
and to direct vented air away from the user or patient. The control
unit housing may be manufactured of a number of suitably strong and
corrosion-resistant materials, including stainless-steel, aluminum,
or molded plastic. Desirably, the components of the control unit
150 are adapted to run on conventional power from a catheterization
lab power outlet, for example.
[0106] The present invention also contemplates the use of two
different control units in sequence, depending on need. For
example, the control unit 150 of FIGS. 5A-5C having a relatively
large heat transfer capacity and large housing can be used
initially to rapidly alter the patient's body temperature.
Subsequently, a smaller unit having an internal battery power
source can be substituted for convenience and economy. Both the
large and small control units desirably define the same sized and
configured cavity for receiving a cassette of the present
invention. In this manner, the cassette may be de-coupled from one
unit, the patient transported with the cassette in place to another
location without the first unit, and the cassette coupled to
another unit for a subsequent operation/therapy. The present
invention also encompasses a situation wherein the cassette is
de-coupled from a first unit and then coupled to a second unit of
the same size. This simply obviates the need to transport control
units with the patient.
Exemplary Control Panel
[0107] FIGS. 5B and 5C illustrate in greater detail the upper
portion 154 of the control unit 150, and in particular the control
panel 160. FIG. 5B shows a facade 172 exploded from the control
panel 160, with the facade shown in FIG. 5C having indicia printed
thereon corresponding to various displays and buttons. (The reader
will notice that the control panel 160 in FIG. 5C is an alternative
embodiment from one shown in other drawings, and includes several
added features and with several buttons and/or displays being
slightly relocated). The following is a description of the physical
characteristics of the control panel 160, with a description of an
exemplary method of using the control panel to follow later in the
description.
[0108] The exemplary control panel 160 of FIG. 5C provides a number
of visual displays, including, from top to bottom along the
centerline, a patient temperature display 174, a target temperature
display 176, a cooling/warming rate display 178, and a system
feedback/status display 180. Other desirable information may be
displayed, either with an additional display, or alternating with
information displayed on one of the screens shown here, or by user
initiated request from one of the screens shown here. For example,
by way of illustration but not limitation, if the ramp rate for
heating or cooling the patient is set by the user, or is calculated
by a control microprocessor, or the projected time to target
temperature is calculated, those values may be shown. The larger
displays for alphanumeric characters are preferably liquid crystal
displays (LCD), while several light emitting diode (LED) status
indicators are also provided. Several graphic icons are positioned
adjacent the left of the upper three LCD displays 174,176, and 178,
to indicate their respective display functions. Specifically, a
patient temperature icon 182a, a target temperature LED 182b, and a
cooling/warming rate LED 182c are provided. Just below the
cooling/warming rate LED 182c, an operational mode LED 182d and
associated vertical series of three mode indicators 184 are
provided. Only one of the indicators 184 lights up at any one time,
depending on whether the system is in the COOLING, WARMING, or
MAINTAINING mode. In lieu of the mode indicators 184, the display
180 may carry the message COOLING PATIENT, WARMING PATIENT, or
MAINTAINING so that the operator can easily identify the mode of
functioning of the controller. There also may be only one patient
temperature icon 182 which has a line of lights that streams upward
if the unit is warming, downward if the unit is cooling, and blinks
stationary if the unit is maintaining. Finally, a power on/off
indicator LED is provided in the lower left corner of the control
panel 160.
[0109] The control panel 160 also exhibits a number of input
buttons including, in descending order on the right side of the
control panel, a Celsius/Fahrenheit display toggle 190, a pair of
target temperature adjustment buttons 192, a pair of
cooling/warming rate adjustment buttons 194, a multi-function/enter
button 196, and a mute audible alarm button 198. The mute audible
alarm button 198 is nested within an LED alarm indicator 200.
Finally, in the lower central portion of the control panel 160, a
stop system operation button 202 permits instant shutdown of the
system.
[0110] With reference again to FIGS. 5A and 5B, the housing
includes a cassette receiver 168 which includes an internal cavity
242 into which a heat exchange cassette of the present invention
can be inserted. In the preferred embodiment, a cassette is
provided as described in greater detail below comprising a
reservoir portion which is in fluid communication with a heat
exchanger. Although not shown, a micro-switch is desirably provided
in the slot 168 mounted on one of the walls of the cassette
receiver cavity to indicate when the heat exchange cassette has
been fully inserted into the internal cavity 242, and is engaged
therein for proper operation of the system. Also not shown but well
known in the relevant art, registration means such as pressure pins
or balls and mating detents may be provided in the control unit and
cassette respectively to aid in the correct relative positioning
between the cassette and the control unit. This arrangement also
provides, in some embodiments, for simultaneous engagement of the
motor and fluid connections to the cassette, providing for easy
insertion and setup of the cassette.
[0111] Referring now to FIG. 6, the primary and secondary cooling
circuits utilized by a preferred embodiment of the present
invention will now be described. In the embodiment shown, a primary
fluid circuit 215 comprises a pump 217 that draws primary circuit
fluid from a primary circuit reservoir 219. The primary circuit
fluid is pumped under pressure through line 218 through a primary
circuit heat exchanger 221. As described above, primary circuit
heat exchanger may include a heater/cooler, such as thermoelectric
heater/cooler for heating or cooling the primary circuit fluid. A
blower 223 may be included to assist in removal of excess heat
generated by the heater/cooler or to provide the thermal gradients
required for proper operation of the heater/cooler. Alternatively,
other means for heating or cooling the primary circuit fluid may be
used, such as a water bath that can be heated or cooled as desired,
or by using a suitable compressor operating a refrigeration cycle
that is familiar to those skilled in the art. For example, use of
refrigeration to cool the primary fluid would require some way to
warm the primary fluid, such as, for example, a heat pump,
resistive heating, radio frequency (RF), microwave or other
suitable heating method. Similarly, cooling of the primary circuit
can be provided by an ice bath, or other suitable stored energy
source such as compressed or liquefied gas, or endothermic reactive
chemicals. The primary fluid circuit may be any suitable fluid or
gas, and is not required to be bio-compatible. In other instances,
the primary fluid circuit may be bio-compatible, such as for
example, saline. The fluid may also be a suitable slurry, such as
slush of brine or other fluid.
[0112] The temperature of the fluid circulating within the primary
fluid circuit line downstream of the heat exchanger 221 is sensed
using a suitable temperature sensor, such as, for example, a
thermocouple or thermistor 224, 273, that provide temperature
signals to, for example, a thermoelectric controller 235.
Alternatively, the temperature signals may be sent to system
controller 237. Those skilled in the art will understand that the
function of thermoelectric controller 235 may be included in the
functions carried out by system controller 237, and thus the scope
of the invention does not require a separate thermoelectric
controller.
[0113] In this embodiment, temperature sensor 273 monitors the
temperature of the primary fluid returning to the reservoir 219.
The signals from this sensor may be used to continuously monitor
and calculate the cooling or heating power being delivered. The
power may be calculated because the inlet temperature to the heat
exchanger 229 is measured by temperature sensor 224, and the pump
speed, and thus the speed of flow through the heat exchanger, is
also known. The calculation of power from these values is well
known by those skilled in the art. Monitoring the power is useful
because a change in power may indicate a problem, either in the
primary loop or the secondary cooling loop. For example, should the
primary fluid circuit experience a drop in fluid flow or a decrease
in heat exchange, the temperature of the primary circuit sensed at
temperature sensor 224 would decrease when cooling, or rise when
heating. Upon receiving the temperature signal from sensor 224, the
controller may cause a variety of actions to occur to ensure the
safety of the patient. For example, the controller may stop the
pump and cause an alarm to be sounded.
[0114] In the depicted embodiment, the primary fluid circuit 215
includes a valve 225 and a valve 227 to control the path the fluid
circulating within the primary fluid takes. In this embodiment,
valve 225 is a solenoid valve that is normally closed, and valve
227 is a solenoid valve that is normally open. Both valves 225 and
227 are controlled by signals from controller 237. In this
arrangement, fluid exiting the primary heat exchanger 221 is
diverted by valve 225 into cut off line 226, where normally open
valve 227 provides an open pathway for the circulating fluid to
return to primary fluid reservoir 219 through line 239. In this
manner, the present invention provides a closed loop that allows
for continuous pumping of primary circuit fluid through primary
heat exchanger 221 and into primary fluid circuit reservoir 219
when heat exchanger 229 is not connected to the system, allowing
the temperature of the primary fluid circuit 215 to be heated or
cooled as desired, and then maintained at a temperature, ready to
provide a large stored amount of heating or cooling when the
operator controls the system to beginning heating or cooling the
blood of the patient. The advantages of such a system will be
discussed in more detail below.
[0115] The interface between primary fluid circuit 215 and
secondary fluid circuit 255 is provided by heat exchanger 229. As
shown, heat exchanger 229 provides the means to transfer heat
energy, either in heating or cooling mode, between the primary and
secondary fluid circuits 215 and 255.
[0116] Heat exchanger 229 includes a pair of fluid pathways, which
be thought of as intermediate fluid pathways. These two
intermediate pathways, a primary intermediate pathway and a
secondary intermediate fluid pathway, are physically separated from
each other, but are in thermal communication with each other. This
provides for the exchange of heat energy between the intermediate
fluid pathways, while preventing the possibility of contaminating
the secondary heat exchange fluid which may flow into a patient
with primary fluid circuit fluid, which may or may not be
biocompatible. Similarly, the physical separation of the primary
and secondary intermediate fluid pathways prevent the contamination
of the primary fluid circuit should blood or other bodily fluids
invade the secondary fluid circuit.
[0117] These intermediate fluid pathways, when connected to their
respective primary or secondary fluid circuits, increase the volume
of these circuits. This provides several advantages that will be
discussed in more detail below.
[0118] Secondary fluid circuit 255 comprises a cassette 257 that
includes heat exchanger 229, a secondary fluid circuit reservoir
259 and secondary fluid circuit pump 261. Fluid contained within
secondary fluid circuit 255 is drawn from reservoir 259 by pump 261
and forced down supply line 265 to a heat exchanger 263, such as a
balloon mounted on a distal end of a catheter, as described
previously, that has been positioned within a patient's blood
vessels. After the secondary fluid has passed through heat
exchanger 263, the fluid flows through return line 267 to heat
exchanger 229 and then back into reservoir 259 to complete the
closed loop of the secondary fluid circuit 255. In an alternative
embodiment, the order of heat exchanger 263 and heat exchanger 229
are reversed so pump 261 forces fluid through the secondary side of
heat exchanger 229 and then down supply line 265, and return line
267 empties into reservoir 259. A separate fluid supply 269, such
as a bag of saline, may also be in fluid communication with the
secondary fluid circuit through appropriate lines and valves to
provide a source for additional secondary fluid should for priming
the secondary fluid circuit or to make up any secondary fluid that
is inadvertently lost during treatment of a patient. Fluid supply
269 and reservoir 259 provide compliance for the secondary fluid
circuit to accommodate volume changes in the fluid circuit due to
heating and cooling of the fluid circuit. Similarly, the primary
fluid tank 219 provides compliance for the primary fluid
circuit.
[0119] The temperature of the secondary fluid circulating through
the secondary fluid circuit may be measured using temperature
sensors, such as sensors 270, 271, whose signals are communicated
to controller 237. These, and other signals, may then be used by
controller 237 to control the heating and cooling of the patient by
controlling the heating and cooling of the primary fluid circuit or
to provide an alarm or take other action should the values of the
signals sensed by sensors 270, 271 indicate that the device is not
functioning properly. Additionally, controller 237 may control the
speed of pump 261 independently, or in conjunction with controlling
heat exchanger 221, to heat or cool the patient to a desired
temperature at a desired rate of temperature change.
[0120] The primary fluid circuit side of heat exchanger 229 is
removably connected to the primary fluid circuit using quick
connect/shutoff valves 231, 233. Use of these quick connects allows
the heat exchanger 229 to be removed from the primary fluid circuit
without a substantial loss of primary fluid circuit fluid.
Additionally, primary circuit fluid will not flow into heat
exchanger 229 unless controller 237 provides a valve open signal to
normally closed valve 225. As will be apparent to those skilled in
the art, when the controller 237 provides a valve open signal to
normally closed valve 225, controller 237 also provides a valve
closed signal to normally open valve 227 located in cutoff line 226
to close off cutoff line 226 from the primary fluid circuit,
ensuring that all primary fluid circuit is directed through heat
exchanger 229.
[0121] As noted above, this arrangement is advantageous as it
provides for continuous circulation of primary fluid within primary
fluid circuit 215, which allows the temperature of the primary
fluid circuit 215 to be heated or cooled to a desired temperature,
and then held at that temperature, even if a patient is not being
treated at the time. This is particularly advantageous where a
patient requires rapid heating or cooling. In some prior art
systems, the cooling media used to cool the patient by necessity
was a room temperature at the beginning of treatment. Thus, the
rate of cooling or heating of the patient was dependent on the
ability of the system to add heat to or remove heat from the
cooling media. This could be problematic in the event rapid cooling
of the patient was desirable, since in many cases the system was
not capable of removing heat from the patient's blood at a rate
sufficient to achieve the desired cooling rate.
[0122] The system of the present invention addresses this need by
providing a reservoir of already cooled (or heated, depending on
the needs of the emergency) primary circuit fluid. Since the
primary fluid is already cooled, the rate of cooling no longer
depends solely on the cooling capacity of heater/cooler 221, but
rather on the combined cooling capacity of the pre-cooled fluid and
heater/cooler 221. In effect, this embodiment of the present
invention provides what the inventor has identified as a "turbo
boost" in the heating/cooling capacity of the system that is
helpful where a patient needs to be rapidly cooled or warmed to
provide an enhanced therapeutic effect. The relative amount of
"turbo boost" can be adjusted by adjusting the temperature of the
primary fluid in the primary fluid reservoir, or by increasing the
size of primary fluid reservoir 219, or both.
[0123] In an alternative embodiment, the supply line 265 and the
return line 267 may include couplers, such as luer lock fittings
275, 277. Such an arrangement is advantageous in that it allows the
cassette to be disconnected from the catheter 263 during treatment
of the patient, if necessary. In another embodiment, the heat
exchanger may include connections for connecting a sensor line from
sensors associated with the catheter such that the sensor line is
connected to the command processor at or about the same time that
the access points are connected, thus facilitating rapid set up of
the system.
[0124] In yet another alternative embodiment, the access points in
the primary fluid circuit allow the primary fluid reservoir to be
easily filled with primary fluid. Additionally, the access points
allow for draining the primary fluid reservoir of primary fluid to
facilitate replacement of the reservoir, shipment of the device as
otherwise deemed necessary for convenience or safety.
[0125] In still another embodiment, the primary fluid circuit may
include a means for ensuring that the electrical resistivity of the
primary fluid remains above a predetermined threshold to ensure the
electrical isolation of the primary fluid circuit and the safety of
the patient. One means for accomplishing this is to include a
de-ionizing cartridge 282 containing a suitable ion-exchange resin
in the primary fluid circuit. The flow through the de-ionizing
cartridge may be controlled to allow the entirety of the fluid
circulating in the primary fluid circuit to flow through cartridge
282, or it may be controlled to treat only a portion of the fluid
returning through the primary loop into the tank 219.
[0126] In yet another embodiment, the access points allow the heat
exchanger to be easily and rapidly disconnected from the primary
fluid circuit in the event of a power failure or other problem. In
this manner, an alternative method of providing primary fluid can
be used, such as, for example, circulating ice water through the
primary fluid side of the heat exchange using a system suitable
configured to do so.
[0127] To protect the primary fluid circuit 215 and pump 217
against overloads where valves 225 and 227 are both closed, an
internal bypass loop 284 may be disposed in the primary fluid
circuit. Bypass loop 284 may include a check valve 286 which is set
to open a predetermined pressure that is low enough to prevent
damage to the pump. The inclusion of the bypass loop is also
advantageous in that any blockage of the heat exchanger 229 or
inadvertent disconnection of quick couplings 231 or 233, that
results in increased primary circuit pressures which may damage the
heat exchanger 229 may also be relieved by setting the opening
pressure of check valve 286 at an appropriate level.
[0128] An active or passive vent valve 280 may also be included in
the secondary fluid circuit. Inclusion of this valve is useful in
venting air from the secondary fluid circuit to assist in priming
the secondary circuit with secondary circuit fluid prior to use of
the cassette.
[0129] In an alternative embodiment, monitoring and controlling the
performance of the system may be carried out by monitoring the
temperature in the primary fluid circuit only. Monitoring the
temperature of the primary circuit provides information to the
controller that may be used to calculate the amount of heat energy
that needs to be added to or subtracted from the primary fluid
circuit so as to drive the heat exchange ability of the secondary
fluid circuit to alter the temperature of the patient's tissue or
blood.
[0130] FIG. 7 depicts an alternative embodiment of the system of
the present invention. In this embodiment, the flow through primary
fluid circuit 310 and secondary fluid circuit 312 are altered. As
depicted, primary fluid circuit pump 217 now draws fluid through
heat exchanger 229 rather than pumping fluid through it as shown in
FIG. 6. Moreover, normally closed valve 225 is located between
reservoir 219 and heat exchanger 229. Thus, heat exchanger 229 is
located on the negative pressure side of pump 217. Similarly,
secondary fluid flow through heat exchanger 229 is reversed,
necessitated by the change in flow direction of the primary fluid
circuit. An active or passive vent valve 313, vent line 314 and
vent filter 315 are also in fluid communication with the primary
fluid circuit on the negative pressure side of pump 217.
[0131] There are several advantages of this arrangement. One
inconvenience posed by using a removable heat exchanger 229 is the
need to empty the heat exchanger 229 of primary circuit fluid when
the heat exchanger 229 is detached from the primary fluid circuit.
This arrangement addresses that inconvenience by allowing pump 217
to empty heat exchanger 229 of primary circuit fluid before the
heat exchanger is detached. For example, when the heat exchanger is
to be detached after providing treatment to a patient, an operator,
using the manual input unit (FIG. 5), can direct the controller 237
to send a valve close signal to valves 225 and 227 and a valve open
signal to vent valve 313. This effectively closes off the supply of
primary fluid from the reservoir feeding pump 217, but opens a path
to the air through vent valve 313, vent line 314 and vent filter
315. This allows the pump to suck the primary fluid from heat
exchanger 229 and pump the fluid into reservoir 219 for storage.
When the primary side of heat exchanger 229 has been exhausted of
primary fluid, the controller 237, either automatically having
sensed that the fluid is exhausted, or after receiving a manual
command from the operator, sends a valve close signal to vent valve
313 and a valve open signal to valve 227 to close off the vent line
and restore fluid flow through cutoff line 226. It will be
understood that while the above has been described with reference
to various valve open and valve close signals, where normally open
or normally closed valves are used, no signal will be necessary to
place the valves in their normal state. Rather, the controller may
simply stop providing a signal that places the valve in an other
than normal state. In an alternative embodiment, the vent valve
could be in communication with the inlet side of the pump 217 in
FIG. 6. Such an arrangement would require an additional valve.
However, this arrangement, while workable, is not preferable.
[0132] A further advantage to the embodiment of the present
invention depicted in FIG. 7 is that placing heat exchanger 229 on
the negative pressure side of the pump facilitates keeping the
secondary primary circuit at an increased pressure relative to the
pressure of the primary fluid circuit, which enhances the safety of
the system should a leak develop in the primary fluid circuit of
heat exchanger 229 by preventing encroachment of the primary fluid
into the secondary fluid circuit. Alternatively, the secondary
circuit could be controlled so as to have a higher pressure than
the primary circuit by having the pump push secondary fluid through
the heat exchanger 229 and then through the catheter.
Exemplary Electronic Control Circuit
[0133] As an alternative to the control system described in
conjunction with FIGS. 3A-3B and the graph of FIG. 4, the
controller may employ a cascading PID control scheme. In such a
scheme, a control system is provided that may be divided into two
sections: (a) a Bulk PID control section which takes input from the
user (in the embodiment shown, RAMP RATE and TARGET TEMPERATURE)
and input from the sensors on the patient representing patient
temperature, and calculates an intermediate set point temperature
(SPI) and an output signal to the primary fluid PID control; and
(b) the primary fluid PID control, that receives input from the
bulk PID control section and from a sensor representing the
temperature of the primary fluid, and generates a signal that
controls the temperature of the TE cooler by varying the power
input to the TE cooler. The primary fluid circulates in heat
transfer proximity to the TE cooler, so the primary fluid PID
essentially controls the temperature of the primary fluid. In this
way, the control scheme is able to automatically achieve a
specified target temperature at a specified RAMP RATE based on
input from sensors placed on the patient and the logic built into
the controller. Additionally, this scheme allows the unit to
automatically alter the patient temperature very gradually the last
few tenths of a degree to achieve the target temperature very
gently and avoid overshoot or dramatic and potentially damaging
swings in the electronic power to the TE cooler. Once the target
temperature is achieved, the system continues to operate
automatically to add or remove heat at precisely the rate necessary
to maintain the patient at the target temperature.
[0134] Specifically, this is achieved as illustrated in FIG. 8.
FIG. 8 illustrates an exemplary control schematic of components of
the present invention specifically adapted for use in control unit
150 of FIG. 5A, but applicable to any control unit described
herein. Some of these elements correspond to elements identified
previously, and thus, where appropriate, reference numbers will be
repeated for clarity. In general, the control circuit includes a
control board having a number of logical components indicated
within the dashed line 322, a user input 324, a display output 326,
a plurality of sensors 328, a number of elements of electronic
hardware indicated within the box 330, and a safety system 332. The
user inputs 324 and display outputs 326 were described above with
respect to the control panel 160 of FIG. 5C. The two user inputs
324 applicable to the control circuit in this embodiment are the
target temperature adjustment buttons 192 and cooling/warming rate
adjustment buttons 194. The display outputs 326 applicable to the
control circuit are the patient temperature display 174 and the
alarm display 200, but may include a number of other displays for
various feedback to the user. A plurality of sensors 328 may be
provided, including at least a sensor 327 that senses the patient's
actual body temperature and generates a signal represented by line
326, and a sensor 329 that directly or indirectly senses the
temperature of the primary fluid and generates a representative
signal 331.
[0135] After the system is primed, a set point temperature (SP1) is
determined with a set point calculator 334 using the target
temperature and the desire ramp rate as inputs. This set point
temperature represents an interim target temperature that the
system will achieve at any given time, for example 0.1.degree. C.
each 6 minutes, if the ramp rate is 1.degree. C. per hour, starting
with the initial patient temperature. This set point temperature is
transmitted to a Bulk PID control section 336 of the control board.
The Bulk PID control 336 also receives input from the body
temperature sensor 327.
[0136] Based on the differential between the SP1 and actual body
temperature, if any, the Bulk PID control 336 raises or lowers the
temperature specified for the heat exchange fluid that will be
circulated through the secondary fluid circuit so as to induce a
change to the patient temperature at the specified ramp rate. That
is, a value for the desired primary fluid temperature, or a second
set point temperature (SP2), is transmitted to a primary fluid PID
control unit 338 as illustrated at 337. The primary fluid PID
control unit 338 also receives input from the temperature sensor
329 for the primary fluid as illustrated at 333. The primary fluid
PID control unit 338 compares the sensed primary fluid temperature
with the desired primary fluid temperature transmitted from the
bulk PID control to determine a differential, if any. Based on this
differential, the primary fluid PID control 338 transmits a digital
signal as illustrated at 340 to an "H-Bridge" polarity switching
unit 342, which directs power of an appropriate magnitude and
polarity to the TE cooler 348 to cause the TE heater/cooler to be
heated or cooled to drive the temperature of the primary fluid to
an appropriate level to drive the temperature of the secondary
fluid to heat or cool the temperature of a patient's tissue or
blood toward the desired temperature, or maintain it at that
temperature.
[0137] The polarity switching unit 342 receives power from a source
344 and transforms that power to the appropriate magnitude and
polarity requested by the primary fluid PID control unit. Between
the power source and the polarity switching unit is a safety relay
346 actuated by the safety system 332 that will, in the absence of
a safety issue, transmit the power from the power source 344 to the
polarity switching unit 342. If the safety system 332 is aware of a
safety issue, for example if a low fluid level is sensed, it may
direct the safety relay 346 to open and prevent power from the
power supply 344 from being directed to the TE cooler 348. In the
absence of any safety issue, however, the polarity switching unit
342 transmits the power to the heater/cooler unit 348 in accordance
to the request from the primary fluid PID control unit. Various
subsystems of the present invention provide input to the safety
system 332, and will be described below when introduced.
[0138] The control circuit includes logic that permits rapid heat
exchange when the target temperature and the sensed body
temperature are relatively far apart, and which slows down the rate
of heat exchange as the sensed body temperature nears the target
temperature. As the sensed patient temperature and the SP1 become
very close, the Bulk PID will dictate only a very small change in
the primary fluid temperature, and thus the rate of change will
become smaller and smaller as the SP1 becomes very close to the
sensed patient temperature until the rate of change is essentially
non-existent. In this way, the patient temperature may be very
gently is heated or cooled the last few tenths of a degree,
avoiding overshoot or dramatic swings from heating to cooling when
the body temperature is at the target temperature. As the input
TARGET TEMPERATURE is reached, the SP1 and the TARGET TEMPERATURE
are essentially the same, and the system operates to set the power
to the TE cooler at a level that maintains the necessary primary
fluid circuit temperature to hold the patient temperature at the
TARGET TEMPERATURE. In this way, the system will work to maintain a
target temperature with the primary fluid maintained at just the
right temperature to add or remove heat at the precise rate
necessary to maintain that target temperature as essentially a
steady state.
[0139] The primary fluid PID control 338 samples its respective
inputs at a rate of 10 times a second and updates the output to the
polarity switching unit 342 at a rate of once every second, and
thus the trends of changing patient temperature are constantly
monitored and adjusted. The Bulk PID control 336 samples its inputs
at the same rate, and thus a new target temperature or a new ramp
rate can be specified by the user with nearly instantaneous system
response.
[0140] The controller of the present invention may also be used to
control other aspects of the cooling system. For example, in one
embodiment, when the temperature of the patient approaches within
0.3 degrees of the target temperature, the controller may decrease
the output of the secondary fluid circuit pump, may decrease the
output of the primary fluid circuit pump, and/or reduce the speed
of the fan/blower on the primary circuit to reduce the amount of
noise generated by the apparatus.
Exemplary Heat Exchange Unit
[0141] FIG. 9 is an exploded view of an exemplary embodiment of a
heat exchange cassette 400 of the present invention. Heat exchange
cassette 400 includes a cassette section 405 containing a reservoir
compartment, secondary circuit pump and a heat exchanger 410 for
exchanging heat energy between the primary and secondary fluid
circuits.
[0142] Heat exchanger 410 comprises a heat exchange section 415
disposed within a cavity formed between a base plate 420 and cover
425. O-ring bushings 427 are used to seal fluid passageways inside
of the cavity to facilitate fluid flow though the heat exchange
section 415. The cover 425 is held to the base plate 420 by
connector 430, which may be a threaded screw or bolt, or other
device capable of attaching the base plate to the cover. The entire
heat exchanger 410 is attached to the cassette section 405 using
suitable connectors 435. FIG. 9 also shows connectors 440 which
releasably attach a mounting cover to the reservoir
compartment.
[0143] The base plate 420 also includes two fluid channels (not
shown), to be discussed in more detail below. The inlet of the
first fluid channel receives secondary fluid returning from the
catheter and the inlet of the second fluid channel receives priming
fluid to fill the heat exchanger with secondary fluid before use.
The outlets of both the first and second fluid channels are fluidly
connected to the inlet 429 of the heat exchanger. Heat exchanger
outlet 431 is fluidly connected to the reservoir in the cassette
section 405.
[0144] Also shown in FIG. 9 are a variety of fluid connectors for
completing the fluid paths of the primary and secondary fluid
circuits. For example, connectors 445 and 450 are mounted on cover
425 and are used as input and output ports for communicating fluid
through the primary circuit side of the heat exchanger 415.
Similarly, barb 455 is disposed in the output fluid path of the
secondary fluid circuit pump, and provides for connection to the
supply line that provides secondary fluid to the balloon of the
catheter that is used to heat or cool a patient's blood. Barb 460
receives the return line from the catheter and provides an input
though the first fluid channel in the base plate 420 into inlet of
the secondary side of heat exchanger 415.
[0145] After secondary circuit fluid has flowed through heat
exchanger 415, the secondary fluid exits the heat exchanger 415
through outlet 431 and flows out barb 470 into the reservoir of
cassette section 405 through barb 480. Barbs 465 and 469 provide
access to the secondary fluid circuit to prime the secondary fluid
circuit with secondary fluid, and barb 475 allows the reservoir in
cassette section 405 to be vented.
[0146] FIGS. 10 and 10A depict an exemplary embodiment showing the
secondary circuit tubing connections to the heat exchange cassette
400. Supply tubing 505 to the balloon catheter is connected to barb
455 (FIG. 9), and return tubing 510 is connected to barb 460. As
described above, barb 460 is connected via the first fluid channel
in base plate 420 to the inlet 429 of the secondary side of the
heat exchanger. Fluid supply line 515, which includes a spike 520
covered by spike cover 525, is connected to splitter block 540.
Splitter block 540 includes barb 550 which is connected by a short
length of tubing (not shown) to barb 469. A low pressure check
valve 560 is disposed between and connects barbs 545 and 465. Barb
465 is fluidly connected to the second fluid channel in base plate
420, and provides fluid access to the secondary side of the heat
exchanger to allow the heat exchanger to be primed with secondary
circuit fluid when necessary. Vent line 530, which includes an
active or passive vent valve 535 is connected to barb 475.
[0147] The secondary fluid circuit may be primed with secondary
fluid by inserting spike 520 into a fluid source. Fluid flows into
spike 520 and through line 515 and into splitter 540, where the
fluid stream is divided. Fluid then flows into the heat exchanger
through check valve 560 and barb 465 and into the second fluid
channel in base place 520 and finally into the inlet 429 of the
heat exchanger. Simultaneously, fluid flows into the reservoir of
the cassette section through barb 469. Check valve 560 is a one way
valve that allows fluid to flow during priming, but prevents flow
in the opposite direction, as would occur during operation of the
secondary fluid circuit when fluid under pressure from the return
line would be present at the inlet of the heat exchanger. This
arrangement is advantageous in that it allows the reservoir and
heat exchanger to be primed simultaneously.
[0148] In another embodiment, lines 515 and 530 may include valves
that may be automatically actuated to facilitate automatic priming
of the secondary fluid circuit. In one preferred embodiment, lines
515 and 530 run through a electrically actuatable clamp. When the
operator of the system presses a button, for example, a PRIME
button on the controller or controller display, the controller
commands the clamp to open. At this time, fluid flows from the
fluid source into the reservoir, and air is allowed to vent from
the system. Typically, the fluid from the fluid source fills the
reservoir via gravity, but a pressure cuff, or other similar means,
may be applied to the fluid source to increase the rate of fluid
flow, and thus decrease the time needed to prime the secondary
fluid circuit. When the level in the reservoir is determined to be
full, utilizing the sensing system previously described, controller
closes the clamp or valve controlling flow through vent line 515.
The clamp or valve on line 530 may remain open to allow the fluid
source to accommodate volume changes that occur due to temperature
changes and or pressure changes in the secondary fluid circuit
during operation.
[0149] FIGS. 11A and B depict additional detail of an exemplary
embodiment of the cassette section 405. Referring to FIG. 11A, the
cassette section 405 is shown in the reverse orientation in which
it is inserted into the control unit (FIG. 2). Cassette section 405
includes a cassette block 605 which, as is seen in FIG. 11B, has
side walls that form a reservoir 607. Also visible on the bottom
surface of cassette block 605 in FIG. 11A is a window 615 which
provides for transmission of light beams into the reservoir for use
in determining the fluid level within the reservoir 607. Pump
coupler 610 is also disposed on the bottom surface of the cassette
block 605, and is configured to couple to pump driver 68 (FIG. 2)
to drive the secondary fluid circuit pump.
[0150] The top side of cassette block 605 is closed by cover 620.
Cover 620 is typically opaque, and includes a mirror 625 disposed
on an inside surface of the cover 620. Mirror 625 forms part of a
fluid level sensor that is used to determine the level of secondary
circuit fluid within reservoir 607. Also shown are pump seal 630
and pump shaft bushings 635, which will be described in more detail
with reference to FIG. 11B.
[0151] FIG. 11B depicts the cassette section 405 in a right side up
orientation so as to facilitate discussions of additional details
of the structure and components of the cassette section 405. As
described above, the sides walls of cassette block 605 and the
cover 620 form a secondary fluid circuit reservoir 607 within
cassette section 605. A prism 655 which forms a portion of the
above described level sensor is mounted on an inner surface of the
cassette block, and is in light communication with window 615
disposed on the top surface of cassette block 605.
[0152] In an alternative embodiment, two prism may be used to
provide a redundant system. In such an arrangement, the controller
may also have two processors, one main processor and a safety
processor. The main processor monitors the first prism, and the
safety processor monitors the second prism. The monitoring of the
prisms may be timed by the processors such that the main processor
should detect any abnormalities before the safety processor does.
Thus, an alert may be sent to the user and the pump will stop. In
this case, the pump may be restarted. If the abnormality is not
corrected and is detected by the safety processor, the pump may be
stopped and require intervention to determine the cause of the
abnormality before treatment may proceed. Alternatively, both
safety systems may function simultaneously and with equal priority,
so that a low level indicator by either one will trigger a signal
to the user such as an alarm, or will stop the pump.
[0153] Disposed within the reservoir 607 is secondary fluid circuit
pump 660. In the depicted embodiment, pump 660 is a gear pump
having a pair of pumping gears 665 each mounted on a pump shaft 677
disposed within a pump body 679. A backing plate 670 holds shafts
677 in place within the pump, and a height compensator 675, which
is typically formed from a compressible material, such as a
biocompatible plastic such as, for example, silicon, is disposed on
the shafts between the backing plate 670 and the end of the shafts.
The height compensator supplies pressure onto the pump gears to
hold the gears in place while allowing some movement of the gears
so they may freely rotate. Cover 620, which is shown inverted in
FIG. 11B, is held in place on cassette block 605 to form reservoir
607 using suitable connectors 680.
[0154] Also disposed in reservoir 607 is an air trap 685. Air trap
685 is made from a porous material that allows secondary fluid to
flow through the air trap, but blocks the flow of air. Air trap 685
may be formed from any material that preferentially allows fluid to
flow but blocks the flow of air, for example, such as a semi
permeable membrane or a foam block. Although the air trap may be
omitted in some embodiments of the present invention, use of air
trap 685 is advantageous as it provides a means for trapping air
bubbles, either large of small, entrained in the secondary circuit
fluid before the fluid enters the secondary circuit pump.
[0155] In an alternative embodiment, where the cassette reservoir
is sufficiently isolated using luer lock connectors and check
valves, the cassette reservoir may be pre-filled with secondary
fluid. Providing such a pre-filled reservoir would eliminate the
need to prime the secondary fluid circuit with secondary fluid
before operating the pump. In such an arrangement, a fluid used to
fill the fluid pathways of the catheter could be made up by
attaching the priming line to a fluid source, if necessary.
[0156] It will be understood that the pump 660 may be located on
the output side of the heat exchanger's secondary fluid circuit to
push secondary fluid through the catheter. Alternatively, the pump
660 may also be located on the inlet side of the heat exchanger's
secondary fluid circuit.
[0157] In an alternative embodiment, a suitably flexible cooling
balloon can be mounted on the catheter such that pulsations in the
secondary fluid caused by the pump result in fluctuation of the
balloon. Such fluctuation of the balloon may be advantages in
promoting better heat transfer between a patient's blood and the
cooling fluid in the balloon by inducing turbulence in the blood
flow adjacent to the surface of the balloon.
Safety Systems
[0158] As described previously, the reservoir section can be
provided with a means to monitor the amount of heat exchange fluid
that is in the system, more specifically an optical means for
detecting the level of fluid contained within the fluid reservoir.
Since the secondary fluid is a biocompatible fluid and the volume
of the external source is only about 250 ml, it is not expected
that fluid leakage into the patient will be problematic. It would
be undesirable, however, to have the fluid level fall so low that
air is pumped into a patient. Therefore the heat exchange fluid
supply system of the invention is designed to detect the level of
the fluid in the system so that a warning or other measure can be
instituted if the system becomes unacceptably low. As shown in
FIGS. 11A and B, a pair of prisms 655 are mounted to the cassette
block 605 each having a corresponding beam source and beam, are
utilized to form a fluid level sensor. Each prism 655 will have a
corresponding beam source and sensor mounted on the control unit at
a location adjacent to the prism.
[0159] As seen in FIG. 11A, the transparent window 615 disposed in
the bottom surface of the cassette block 605 allows for optical
monitoring of the fluid level in the reservoir 607. An adjacent
beam source and sensor would also be provided for the second prism
655, if present.
[0160] Typically, the beam source(s) and sensor(s) would be
positioned on the control unit at a location so as to access the
interior of reservoir 607 through the window 615. The prisms 655
have a diffraction surface and may be molded or machined separately
using a material such as polycarbonate and then affixed within the
reservoir section, or they may be machined as part of the section.
Again, although only one prism is needed for the fluid level
detection method to function, it may be desirable to include a
second redundant prism described below.
[0161] The second prism/source/sensor is redundant and functions to
monitor the same fluid level as the first prism but operates as a
safety mechanism in the even the first prism/source/sensor fails to
function properly. Alternatively, one of the prisms may also have a
"high level" sensing system that can be used to signal the control
unit when the fluid in the reservoir reaches a certain high level.
This is useful, for example, when a valved-priming system is used
and detection of a high or full level is needed to determine when
to activate the valve to stop the priming sequence. If desired,
both high level and low level sensors can be employed on each
prism. The sensors will generate a signal indicating that either
there is or is not fluid at the level of the optical beam. If the
optical beam source and sensor are positioned or the optical beam
is directed near the top of the tank, the indication that the fluid
has reached that level will trigger the appropriate response from
the control system, for example to terminate a fill sequence. On
the other hand, if the sensor is positioned or optical beam
directed to sense the fluid level on the bottom of the tank, then
the fluid level detector is configured to detect a low fluid level
and can generates a signal representing such low level. The
controller can then be configured to respond to this signal
indicative of a low level of fluid in the reservoir. For example,
the controller can be designed to be responsive to this signal such
that it controls the secondary circuit pump to stop pumping when a
low fluid level is detected, so that air will not be pumped into
the heat exchange catheter. In addition, an alarm may sound and an
alarm display, such as the display 200 of FIG. 5C, may be activated
to alert the operator to the low fluid level condition.
[0162] In a preferred embodiment of the present invention, several
levels of safety redundancy are provided to prevent failure of the
system, and potential injury to the patient. First, two
microprocessors may be provided and constantly monitored for
agreement. If one fails, the system alarms and shuts. Secondly, two
or more patient sensors may be provided and monitored for
agreement. They are sampled frequently by the controller and if the
values do not agree, as with the microprocessor, the system alarms
and shuts down. Likewise, two or more fluid level sensors for the
heat exchange circulation path desirably agree for redundancy.
Still further, two or more temperature sensors for the heat
exchange medium could be provided and monitored for agreement. In
short, various redundant subsystems of the overall system ensure
proper operation and the feedback therefrom is used to shut off the
system if necessary.
[0163] In another preferred embodiment of the invention, the
reservoir 607 section is provided with a means to detect when the
fluid reservoir is too low. Typically, an optical beam source would
begin operation after the reservoir fills with fluid. In operation,
the optical beam source produces an optical beam that is directed
into the prism from the bottom and is internally reflected one or
more times within the prism at its surface interface with the fluid
and back to the optical beam sensor. As long as fluid is in the
reservoir, the sensor will observe a reflected light beam and the
pump will continue to operate, moving fluid through the heat
exchange cassette and catheter. However, if the fluid level drops
below the upper reflective surfaces of the prism, thus changing the
reflective index at that internal surface, the sensor then will not
observe a reflected light beam. When no such reflected beam is
received, the system sounds an alarm and ceases to pump.
[0164] Additional safety systems that are contemplated by the
invention include bubble or air-in-line detectors at various
locations on the conduits to detect any bubbles or entrained air
that may be pumped into the fluid system and temperature monitors
that may signal if a portion of the system, or the fluid, is at a
temperature that is unacceptably high or low. Moreover, the bubble
or air-in-line detectors may also be configured to indicate whether
an acceptable level of fluid is present within a fluid circuit. A
detector to indicate whether the fluid sensor optical beam sources
are operational may be supplied, for example by placing a detector
located to detect the optical beam initially when the system is
turned on but there is insufficient fluid in the reservoir to cause
the beam to diffract back to the detector. The control unit
depicted in FIGS. 1,2 and 5 provide for multiple patient
temperature sensors. A warning may sound, and the system may shut
down, if the temperature signal from the two different sensors are
dramatically different, indicating that one of the sensors, perhaps
the one driving the control of the system, is misplaced, is not
functioning, has fallen out or the like. Other similar safety and
warning systems are contemplated within the scope of the system of
the invention.
[0165] It should also be understood, in accordance with the present
invention, that the controller processor may be configured to
simultaneously respond to multiple sensors, or to activate or
de-activate various components such as several heat exchangers. In
this way, for example, a controller might heat blood that is
subsequently circulated to the core body in response to a sensed
core body temperature that is below a target temperature for the
core, and simultaneously activate a second heat exchanger to cool
blood that is directed to the brain region in response to a sensed
brain temperature that is above a target temperature for the brain.
It may be that the sensed body temperature is at the target
temperature and thus the heat exchanger that is in contact with
blood circulating to the body core may be turned off by the
controller, while at the same time the controller continues to
activate the second heat exchanger to cool blood that is directed
to the brain region. Any of the many control schemes that may be
anticipated by an operator and programmed into the control unit are
contemplated by this invention.
[0166] One advantage of the various embodiments of the system of
the present invention is that it provides for the exchange of a
large amount of heat between a patient's blood and the cooling
circuits. In order to ensure that a patient's temperature may be
lowered as rapidly as possible, and then maintained, it has been
found to be desirable to maintain the primary fluid circuit at a
temperature in the range of 0-5 degrees centigrade against a
thermal load of greater than 400 watts. However, as those skilled
in the art will understand, maintaining the primary fluid
temperature at such a level is difficult to accomplish. FIG. 12 is
a graphical representation showing how one embodiment of the
present invention performed. This graph shows that the embodiment
tested was able to maintain a primary fluid temperature of less
than 1.5 degrees centigrade under a power load of 500 watts.
[0167] FIG. 13 is a graphical representation illustrating the
performance of one embodiment of the present invention compared to
the performance of prior cooling system when used to cool patients.
Line 700 was derived using the embodiment of the present invention,
and shows how patients were cooled to 33 degrees centigrade in an
average of 19 minutes. This contrasts with the prior system,
depicted by line 710, which required 68 minutes on average to cool
a patient to 33 degrees centigrade. The dashed lines in FIG. 13
depict the 95% confidence interval around the data used to derive
the lines 700, 710.
[0168] Another advantage of the system of the present invention is
that the ability to extract large amounts of heat from the primary
cooling loop provides for reduced time for the system to begin
removing large amounts of thermal energy from the patient. For
example, when needed, the primary cooling loop can be cooled to its
target temperature of less than 3 degrees centigrade in 5 minutes
or less. Such rapid cooling may be needed in an emergent situation
where fast cooling of a patient is desired but where use of such a
system was not anticipated.
[0169] A further advantage of the system of the present invention
is that all of the portions of the system that are in contact with
the patient may be disposable, but substantial and relatively
expensive portions of the system are reusable. Thus, the catheter,
the flow path for sterile heat exchange fluid, the sterile heat
exchange fluid itself, and the pump head are all disposable. Even
if a rupture in the heat exchange balloon permits the heat exchange
fluid channels and thus the pump head to come in contact with a
patient's blood, no cross-contamination will occur between patients
because all those elements are disposable. The pump driver, the
electronic control mechanisms, the heat exchanger, and the manual
input unit, however, are all reusable for economy and convenience.
Desirably, as illustrated, all of these re-usable components are
housed within a single control unit that may be operated by a
single operator in the surgical or general wards of a hospital or
other care giving institution. Likewise, the various sensors
distributed around body and along the catheter may be disposable,
but the controller processor to which they attach is re-usable
without the need for sterilization.
[0170] In another embodiment of the present invention, as shown in
FIG. 6, check valve 286 may be included in the primary fluid
circuit to control the pressure within the primary fluid circuit
should the outlet side of the primary fluid circuit be
disconnected. In some embodiments, the primary fluid circuit pump
is capable of pumping the primary fluid at pressures that greatly
exceed a preselected safety threshold. For example, the pump may be
capable of reaching pressures of 50 psi or more. To provide further
safety to the patient, the check valves in the primary fluid
circuit may be chose so as to prevent the pressure within the
primary circuit from exceeding a pressure that has been determined
to be safe, such as, for example, 35 psi. This prevents the heat
exchanger from ever being exposed to a pressure that might cause a
failure of the primary fluid circuit within the heat exchanger.
This provides for increased safety for the patient, since the
pressure limit prevents the possibility of a catastrophic rupture
heat exchanger fluid circuits and thus prevents the possibility of
circulation of primary fluid, which may be a material such as
alcohol or propylene glycol or the like, into the secondary fluid
circuit, through the catheter, and into the patient.
[0171] The unique combination of fluid lines, connectors and valves
provide many advantages over prior art systems. For example, where
the primary fluid connectors of the cassette include releasable
couplers which fluidly seal, the cassette may be shipped with the
primary fluid circuit of the cassette full of primary cooling
fluid. In another embodiment, the secondary fluid circuit of the
cassette may be pre-filled with secondary cooling fluid and
sterilized, thus eliminating, or at least substantially reducing,
the amount of time and effort needed to prime the secondary fluid
circuit.
[0172] It will also be appreciated by those of skill in the art
that the system described herein may be employed using numerous
substitutions, deletions, and alternatives without deviating from
the spirit of the invention as claimed below. For example, but not
by way of limitation, the primary and secondary fluid pathways in
the heat exchange plate may be a bellows, tube in tube, fan folded
sheet, plate, coil or other suitable configuration, or the sensors
may sense a wide variety of body locations and other parameters may
be provided to the processor, such as temperature or pressure.
Further, the in-dwelling heat exchanger at the end of the catheter
may be any appropriate type, such as a non-balloon heating/cooling
element. An appropriate pump might be provided that is a screw
pump, a gear pump, a diaphragm pump, a peristaltic roller pump, or
any other suitable means for pumping the heat exchange fluid. All
of these and other substitutions obvious to those of skill in the
art are contemplated by this invention.
[0173] Another embodiment of the present invention is configured to
accept supplemental cooling devices that may be used to supplement
the cooling of the primary fluid circuit, the secondary cooling
circuit, or both. In one embodiment, the supplemental cooling
device comprises a vessel having each end sealed with an end cap.
The vessel may be cylindrical, configured as a flat plate, or other
suitable configuration. The interior of the vessel between the two
end caps defines a chamber filled with a cooling medium, which may
be a liquid, such as water, a gel, or a solid such as ice or other
frozen material. An inlet tube extending through one of the end
caps carries a first quick-disconnect fastener for detachably
coupling the inlet tube in fluid communication with a fluid source,
such as the primary or secondary fluid circuit, and an outlet tube
extending through the other end cap, terminated by a second
quick-disconnect for detachably coupling the outlet tube in fluid
communication with the primary or secondary fluid circuits. As
fluid from the primary or secondary fluid circuits enters the inlet
tube, heat energy in the fluid is absorbed by the cooling medium,
and thus the temperature of the fluid flowing through the fluid
circuit is further cooled by the cooling device. This supplemental
cooling provides for an increased rate of temperature reduction in
a patient, which may be beneficial in certain situations. Moreover,
if the amount of cooling required exceeds the cooling capacity of
the main heater/cooler, even with the addition of one supplemental
cooling device, additional supplemental cooling devices may be
coupled into the primary or secondary fluid circuits as desired.
Further, the quick-disconnect couplings allow for replacement of a
supplemental cooling device that has absorbed as much heat energy
as it can with a fresh supplemental cooling device when necessary.
Alternatively, other stored energy sources such as compressed or
liquefied gas, or endothermic reactive chemicals, may be used as
supplemental cooling sources. Additionally, the system may also be
configured with supplemental heating sources to augment the heating
ability of the system to address situations where a patient
requires warming at a higher rate than can be provided by a TE or
resistive heating element alone.
[0174] While particular embodiments of the invention have been
described above for purposes of illustration, it will be evident to
those skilled in the art that numerous variations of the
above-described embodiments may be made without departing from the
invention as defined in the appended claims.
* * * * *