U.S. patent application number 09/930821 was filed with the patent office on 2002-02-14 for unilimb respiratory conduit and components.
Invention is credited to Fukunaga, Atsuo F., Fukunaga, Blanca M..
Application Number | 20020017302 09/930821 |
Document ID | / |
Family ID | 46276402 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020017302 |
Kind Code |
A1 |
Fukunaga, Atsuo F. ; et
al. |
February 14, 2002 |
Unilimb respiratory conduit and components
Abstract
A multilumen unilimb conduit for providing respiratory gases to
and receiving expiratory gases from a patient connected to a
unilimb respiratory circuit. The conduit has unique fittings for
connection to patient devices or assisted ventilation systems and
components. In a preferred embodiment, the conduit has fasteners or
blocking devices at either or both of its distal and proximal
ends.
Inventors: |
Fukunaga, Atsuo F.; (Rancho
Palos Verdes, CA) ; Fukunaga, Blanca M.; (Rancho
Palos Verdes, CA) |
Correspondence
Address: |
Daniel B. Schein, Ph.D., Esq.
BRINKS HOFER GILSON & LIONE
P. O. Box 10395
Chicago
IL
60610
US
|
Family ID: |
46276402 |
Appl. No.: |
09/930821 |
Filed: |
August 15, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09930821 |
Aug 15, 2001 |
|
|
|
09322795 |
May 28, 1999 |
|
|
|
09322795 |
May 28, 1999 |
|
|
|
09018540 |
Feb 4, 1998 |
|
|
|
5983896 |
|
|
|
|
09018540 |
Feb 4, 1998 |
|
|
|
08751316 |
Nov 18, 1996 |
|
|
|
5778872 |
|
|
|
|
Current U.S.
Class: |
128/207.14 ;
128/202.27; 128/911; 128/912; 128/914 |
Current CPC
Class: |
A61M 16/1055 20130101;
Y10S 128/911 20130101; Y10S 128/914 20130101; A61M 16/08 20130101;
A61M 2230/435 20130101; A61M 2230/432 20130101; Y10S 128/912
20130101 |
Class at
Publication: |
128/207.14 ;
128/202.27; 128/911; 128/912; 128/914 |
International
Class: |
A61M 016/00; A62B
009/06 |
Claims
We claim:
1. A unilimb conduit for providing inspiratory gases to a patient
and receiving expiratory gases therefrom, said unilimb conduit
having a distal end and a proximal end, wherein said distal end of
said unilimb conduit is operatively connectable to and detachable
from a patient by a user at a site of use, and said proximal end of
said unilimb conduit is operatively connectable to and detachable
from a proximal terminal by a user at a site of use wherein the
proximal terminal is of the type that has a rigid housing having
first and second conduits which converge at a distal end of the
proximal terminal so as to be capable of simultaneous operative
connection to said proximal end of said unilimb conduit and wherein
the first and second conduits in the proximal terminal diverge from
each other proximally of the distal end of the proximal terminal so
that the first conduit of the proximal terminal may be
independently operatively connected to a source of inspiratory gas
while the second conduit of the proximal terminal may be
independently operatively connected to an expiratory outlet, said
unilimb conduit comprising: a first flexible tube and a second
flexible tube, said tubes defining independent flow paths and each
having a distal end and a proximal end, wherein when said unilimb
conduit is operatively connected to a proximal terminal of said
type, said distal end of said first tube is placed in fluid
communication with the proximal end of the first conduit and
simultaneously said distal end of said second tube is placed in
fluid communication with the proximal end of the second conduit
wherein said first tube may be operatively connected to a source of
inspiratory gas via the proximal terminal while said second tube
may be operatively connected to an expiratory outlet via the
proximal terminal, wherein said unilimb conduit may be operatively
detached from a proximal terminal after use therewith for
independent disposal or sterilization.
2. The unilimb conduit of claim 1, further comprising: a proximal
fitting, said proximal fitting comprising a first pipe and a second
pipe maintained in fixed relationship to each other, said first
pipe and second pipe each having a proximal end and a distal end,
wherein said distal end of said first pipe is operably connected to
said proximal end of said first tube and said distal end of said
second pipe is operably connected to said proximal end of said
second tube, said pipes comprising a material more rigid than the
material forming said first and second tubes.
3. The unilimb conduit of claim 1, further comprising a proximal
terminal operatively connected thereto, wherein said proximal
terminal comprises a rigid housing having first and second conduits
which converge at a distal end of said proximal terminal so as to
be capable of simultaneous operative connection to said proximal
end of said unilimb conduit and wherein said first and second
conduits in said proximal terminal diverge from each other
proximally of said distal end of said proximal terminal so that
said first conduit of said proximal terminal may be independently
operatively connected to a source of inspiratory gas while said
second conduit of said proximal terminal may be independently
operatively connected to an expiratory outlet, wherein said unilimb
conduit can be operatively detached from said proximal terminal for
independent sterilization or disposal.
4. The unilimb conduit of claim 3, wherein said unilimb conduit is
operatively connected through a filter to said proximal
terminal.
5. The unilimb conduit of claim 2, wherein said proximal end of one
of said pipes is capable of being operably connected to an
inspiratory gas input while said proximal end of the other one of
said pipes is operably connected to an exhaust outlet, and wherein
said distal end of said unilimb conduit can be operably connected
to an airway device connected to a mammal, and wherein a user may
utilize said unilimb conduit in an assisted ventilation system by
operable connection of said proximal fitting to an inspiratory gas
input and an expiratory gas outlet in order to provide inspiratory
gases and exhaust expiratory gases from a mammal, and may
disconnect said proximal fitting from the assisted ventilation
system after use.
6. The unilimb conduit of claim 1, wherein the outer diameter of
said first tube is smaller than the inner diameter of said second
tube, said first tube being at least partially disposed within said
second tube, said distal end of said first tube being disposed
within and in direct fluid communication with the interior of said
second tube.
7. The unilimb conduit of claim 1, further comprising a distal
fitting at said distal end of said unilimb conduit which can be
operably connected to an airway device, said distal fitting having
a distal opening therein to permit passage of inspiratory and
expiratory gases therethrough, said distal opening having blocking
means therein to block insertion therein of tubing or fittings.
8. The unilimb conduit of claim 7, wherein said distal fitting
further comprises connector means, said connector means only
permitting connection of said distal fitting to devices having a
mating connector.
9. The unilimb conduit of claim 7, wherein said connector means
includes means for locking engagement with a mating connector on a
device to which said distal fitting is to be attached.
10. An adaptor for connecting components into an assisted
ventilation system, comprising a patient device connector and a
proximal connector, wherein said patient device connector permits
connection to a standard slip fitting on the proximal end of a
patient device selected from the group consisting of an
endotracheal tube, a mask, a filter, a dead space tube, a heat and
moisture exchanger, an artificial nose, a nebulizer, a water trap,
and a coaxial respiratory conduit, and said proximal connector
permits connection to a mating distal connector of an assisted
ventilation system component, the mating distal connector having a
blocking member to prohibit insertion therein of the proximal end
of patient devices other than those having said proximal
connector.
11. The adaptor of claim 10, further comprising means for locking
engagement with the mating distal connector on an assisted
ventilation system component to which the adaptor may be
connected.
12. The adaptor of claim 10, further comprising indicator means for
indicating the status of the connection of said proximal connector
to a mating distal connector, said indicator means being at least
one of the group consisting of a tactile indicator and an audible
indicator.
Description
RELATED U.S. APPLICATION DATA
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 09/018,540, filed Feb. 4, 1998, now U.S. Pat.
No. 5,983,896, issued Nov. 16, 1999, which was a divisional
application of U.S. patent application Ser. No. 08/751,316, filed
Nov. 18, 1996, now U.S. Pat. No. 5,778,872, issued Jul. 14,
1998.
FIELD OF THE INVENTION
[0002] The present invention relates in one aspect to artificial
ventilation methods and systems for administering and exhausting
gases to a mammal, including methods and systems for use in
anesthesia and administration of oxygen to patients, and more
particularly to artificial breathing systems capable of controlling
carbon dioxide rebreathing. The present invention relates in
another aspect to a unilimb inspiratory and expiratory breathing
device for use in a breathing circuit, which has one or more
tubular conduits detachable at a common interface, the interface
optionally providing for control of gas flow and operable
connection to different functional devices. The present invention
also relates to improved components of assisted ventilation systems
and methods for providing same.
BACKGROUND OF THE INVENTION
[0003] Breathing circuits are utilized to conduct inspiratory gases
from a source of same, such as from an anesthetic machine, to a
patient, and to conduct expiratory gases away from the patient. The
gases are conducted through two or more conduits, and, generally,
at least a portion of the expiratory gas is recycled to the patient
after removal of carbon dioxide. To facilitate description of the
prior art and the present invention, the end of a conduit directed
toward a patient shall be referred to as the distal end, and the
end of a conduit facing or connected to a source of inspiratory
gases shall be referred to as the proximal end. Likewise, fittings
and terminals at the distal end of the breathing circuit, e.g.,
connecting to or directed at the patient airway device (i.e.,
endotracheal tube, laryngeal mask, or face mask), will be referred
to as distal fittings or terminals, and fittings and terminals at
the proximal end of the breathing circuit will be referred to as
proximal fittings and terminals. For further information on
breathing systems, and anesthetic and ventilation techniques, see
U.S. Pat. No. 3,556,097; U.S. Pat. No. 3,856,051; U.S. Pat. No.
4,007,737; U.S. Pat. No. 4,188,946; U.S. Pat. No. 4,232,667; U.S.
Pat. No. 5,284,160; Austrian Patent No. 93,941; Dorsch, J. A. and
Dorsch, S. E., Understanding Anesthesia Equipment: Construction,
Care And Complications, Williams & Wilkins Co., Baltimore
(1974) (particularly chapters 5-7); and Andrews, J. J., "Inhaled
Anesthetic Delivery Systems," in Anesthesia, Fourth Edition,
Miller, Ronald, M.D., Editor, Churchill Livingstone Inc., New York
(1986) (particularly pp. 203-207). The text of all documents
referenced herein, including documents referenced within referenced
documents, is hereby incorporated as if same were reproduced in
full below.
[0004] U.S. Pat. No. 4,265,235, to Fukunaga, describes a unilimb
device of universal application for use in different types of
breathing systems, which provides many advantages over prior
systems. The Fukunaga system utilizes a space saving coaxial, or
tube-within-a-tube, design to provide inspiratory gases and remove
expiratory gases. Generally, the inner tube is connected at its
proximal end to a source of inspiratory, fresh gas, while the outer
tube proximal end is connected to an exhaust port and/or to a
carbon dioxide absorber (the latter at least partially exhausts
into the inspiratory gas source when used in a circle system). In
addition to reducing the size of the breathing apparatus connected
to a patient by reducing the number of tubes near the patient, the
Fukunaga system has additional benefits, such as serving as an
artificial nose (expired air warms and humidifies inspired air as
the opposing two flows are co-axial in the unilimb device). The
Fukunaga circuit is also safer than prior co-axial systems, since
the distal end of the inner tube is not connected to the outer tube
at a distal fitting, so that the outer tube can be axially extended
with respect to the inner tube without disconnecting the proximal
end of the inner tube from the source of inspiratory gases; this
safety feature can also be used to increase the dead space between
the distal ends of the inner tube and outer tube, and thereby allow
for adjustment of the amount of expiratory air the patient
rebreaths. Dead space is defined herein as the part of the
breathing circuit external to the patient which, at the end of
expiration, is filled with exhaled gases to be inhaled at the next
breath (generally the expired air in the dead space is combined
with oxygen and/or other gases provided from a source thereof). It
will be appreciated that most known breathing circuits provide a
certain amount of dead space when being used. For example, in the
device shown in Leagre et al., U.S. Pat. No. 5,404,873, the portion
of the breathing circuit that is distal to the end of the
inspiratory tube, plus the area between the face mask and the
patient's face all comprises dead space where inspiratory and
expiratory gases are mixed. The same is true for the device shown
in Leagre, U.S. Pat. No. 5,901,705, except that the dead space also
includes the interior volume of the filter.
[0005] An embodiment of the Fukunaga unilimb device is commercially
manufactured as the UNIVERSAL F.TM. by King Systems Corporation of
Noblesville, Ind., USA. The device includes a proximal terminal
comprising a hollow, T-shaped housing with three ports: an
inspiratory gas port, an expiratory gas port at a perpendicular
angle to the inspiratory gas port, and a third ("patient") port.
The proximal terminal is connected to an outer tube and a coaxial
inner tube, which carry gases to and from the proximal terminal.
The outer tube is flexible and corrugated, and formed of a
transparent (or semi-transparent) material. The proximal end of the
outer tube is sealably connected and bonded to the patient port of
the proximal terminal. The proximal end of a dark colored, flexible
inner tube is sealably connected and bonded to the inspiratory
port, and extends through the T-shaped housing, out the patient
port, and passes through most of the axial length of the outer
tube. The dark color of the inner tube readily permits the user to
see through the outer tube to determine whether the inner tube is
properly connected.
[0006] The inner diameter of the outer tube is sufficiently larger
than the outer diameter of the inner tube to permit adequate
patient respiration. The distal end of the outer tube is sealably
connected and bonded to the exterior of an annular housing which
forms a distal terminal. The annular housing of the distal terminal
is designed to prevent the distal end of the inner tube from
extending beyond the distal end of the outer tube. The entire unit
is designed for disposal after a single use.
[0007] The UNIVERSAL F.TM. device offers great advantages over
prior dual line and unilimb anesthesia circuits, and respiratory
assist devices. However, manufacture of the entire unit requires
several complex steps, and must be done with care so that the inner
and outer tubes are properly sealed and bonded to the proximal
terminal ports at their proximal ends; it is particularly important
that the inner tube proximal end be firmly connected to the
proximal terminal (at the inspiratory port) when the inner tube
carries inspiratory gases, since disconnection during use may not
allow sufficient oxygen and/or anesthetic gases to reach a patient,
which is highly undesirable.
[0008] While U.S. Pat. No. 4,265,235, to Fukunaga, teaches that the
tubes and terminals of such a unilimb device can be detachable from
one another, in practice, the proximal end of the inner tube is
firmly bonded to the inspiratory port, since there remains a risk
that the proximal end of the inner tube could be disconnected from
the inspiratory port during use if a pressure fit (or friction fit)
alone is used. Even if detachment of the inner tube is detected,
the design of prior art unilimb devices does not facilitate the
reconnection of the inner tube to the inspiratory port of the
proximal terminal due to the need to pass the inner tube proximal
end through the length of the proximal terminal via the patient
port so that it can reach and be connected to the inspiratory port.
Thus, the unilimb devices currently used generally comprise a
proximal terminal having an integrally connected inner tube and
outer tube.
[0009] Due to its single-use design, the entire unilimb device,
including the distal terminal, proximal terminal, inner tube and
outer tube, is disposed of after a single use, along with multiple
devices usually connected to the patient nozzle, such as a CO.sub.2
monitor (capnometer), temperature and humidity controlling and
monitoring devices, an O.sub.2 controlling and monitoring device,
and an infection controlling device (e.g., a filter). Thus, in
addition to the inconvenience of requiring fittings (or a housing
accommodating same) for these additional devices at the patient
nozzle or distal terminal, replacement of these fittings, tubing,
and devices after a single use is expensive, and contributes to
ever-growing medical wastes, which are sometimes difficult to find
disposal sites for. All of the systems described in the
aforementioned patents suffer from similar deficiencies. Therefore,
there is a need for an improved unilimb device and ventilation
system which reduces costs and helps the environment by reducing
waste. There is also a need to simplify the construction, and to
increase the safety, efficacy, and reliability of such devices.
[0010] Further, it is believed that devices sold for disposal after
a single use may sometimes be reused in order to save costs, which
may endanger patients. Efforts have been made to make it safer to
reuse some patient respiratory conduit components. One problem with
this is that the exterior of the patient respiratory conduits, as
well as the interior thereof, need to be protected from
contamination, so that contaminants from a first patient do not get
passed on to subsequent patients by adhering to the exterior of
reused components. For example, the device described in Fukunaga
U.S. Pat. No. 4,265,235, discussed above, has a coaxial conduit,
which can be connected at its distal end (i.e., patient end) to a
filter in order to protect the interior of the coaxial conduit from
being contaminated. However, the filter does not protect the
exterior of the coaxial conduit from contamination. One approach to
reducing contamination on the exterior of the conduit is shown in
U.S. Pat. No. 5,901,705, to Leagre, in which a sleeve extends
proximally from a distal (i.e., patient end) filter over the
patient respiratory conduit so that at least the portion thereof
nearest the patient is not exposed to contamination from the
patient. The device shown in the Leagre '705 patent places a
disposable filter at the patient end of the device. The Leagre
device is designed to enable the breathing circuit to be reused on
successive patients since the filter and sleeve prevent
contamination from entering the breathing circuit from the patient;
and prevent contamination in the breathing circuit from entering
the patient. Thus the Leagre '705 patent teaches that the
replacement of the relatively inexpensive, one-time-use filter and
sleeve between patients permits the relatively more expensive
breathing circuit to be used with multiple patients.
[0011] Breathing systems generally provide oxygen to a patient,
while removing carbon dioxide produced by the patient. For example,
in anesthesia, or intensive care, the patient is provided an
artificial breathing atmosphere, in which the physician provides a
mixture of gases to the patient. In addition to providing oxygen
and a variety of vaporized anesthetic agents to the patient, the
physician may permit the patient to rebreath some expired gases.
Rebreathing simply consists of inhaling gases which have been
expired, including carbon dioxide. However, assisted
respiration/ventilation to a patient must be safe, and hypoxia
(i.e., patient oxygen deficiency) must be avoided. Therefore,
inspiratory gases are generally provided at high enough pressure,
tidal volume and respiratory rate (hyperventilation) to ensure that
hypoxia and atelectasis (lung alveolar collapse) is avoided. Thus,
patients are given very high inspired concentrations of oxygen to
avoid hypoxia, but unfortunately they often experience abnormally
low carbon dioxide levels (i.e., hypocarbia or hypocapnia), and
insufficient carbon dioxide can have a negative impact on vital
organs (e.g., brain, heart, splanchnic organs, etc.). However, many
physicians believe that increasing arterial carbon dioxide partial
pressure (P.sub.aCO.sub.2, also referred to as arterial carbon
dioxide tension, often reported as mmHg) in patients by increasing
the carbon dioxide breathed by the patient (e.g., by increasing the
amount of rebreathing) would cause hypoxia. Thus, it was believed
that hypercapnia during assisted ventilation was harmful, since it
was believed it would be associated with hypoxia. Further,
hypocapnia, while it can be harmful, was believed to be less
harmful than hypoxia. Therefore, there remains a need for an
improved artificial ventilation method which controls or avoids
hypocapnia without compromising vital organ tissue perfusion or
oxygenation (i.e., avoids hypoxia).
[0012] Further, there is a need to increase safety of assisted
ventilation systems by reducing the possibility of component
disconnections during use, a need to increase the likelihood that
components provided for single-use only are not reused, and that
devices, such as filters, meet minimum standards to be used in
assisted ventilation systems (as used herein, the terms assisted
ventilation system and/or artificial ventilation system refer to
any device which provides inspiratory gases to a patient and/or
receives expiratory gases from a patient, such as but not limited
to anesthesia machines, artificial ventilators, etc.).
SUMMARY OF THE INVENTION
[0013] The present invention provides in one aspect an improved
assisted or artificial ventilation system utilizing a unilimb
device for providing and exhausting gases from a mammal, and, in
another aspect, an artificial ventilation method which avoids
hypocapnia and hypoxia. Further aspects of the present invention
include new and improved devices for use in the ventilation methods
and systems of the present invention.
[0014] Aspects of the present invention relate to the surprising
discovery by the inventor that concerns about disconnection of the
inner respiratory tube, when connected to the inspiratory port of a
proximal terminal in breathing circuits utilizing a unilimb device,
such as the UNIVERSAL F.TM. circuit or the "Bain" circuit (U.S.
Pat. No. 3,856,051), can be eliminated by the new proximal terminal
construction of the present invention, which facilitates the use of
tubing which is intentionally made to be readily attachable and
detachable to the proximal terminal ports, rather than permanently
sealably connected as in present systems, and yet provide improved
function, safety, and serviceability. The breathing circuit
manufacturing process is greatly simplified by eliminating the
steps of sealably bonding the proximal ends of the inner and outer
flexible respiratory tubes to the inspiratory and patient ports,
respectively, of the unilimb proximal terminal. The new unilimb
proximal terminal of the present invention facilitates the
attachment and detachment of respiratory tubing to the proximal
terminal, thus resulting in a cheaper and safer breathing circuit.
The new unilimb proximal terminal also permits more efficient
placement and utilization of the other breathing circuit components
in a multifunctional interface incorporating the unilimb proximal
terminal. In another aspect of the present invention, an improved
coaxial tube device is provided, which is readily attachable and
detachable from the new proximal terminal. The improved coaxial
tube device has an inner tube in fixed spaced coaxial parallel
relationship to an outer tube at its proximal end, such that a
single step is required to connect both tubes to the proximal
terminal. This is made possible by a fitting within or at the
proximal ends of the coaxial inner and outer tubes, which still
permits the distal end of the inner tube to axially move with
respect to the distal end of the outer tube. As used herein,
coaxial refers to the fact that one tube is contained within the
other, but the central axis of both tubes need not be aligned.
[0015] Aspects of the present invention involve the surprising
discovery by the inventor that hypoxia can be avoided while
simultaneously creating intentional dead space in the breathing
circuit, thereby increasing rebreathing of expired carbon dioxide,
which enables maintenance of normal levels of arterial blood carbon
dioxide (i.e., normocapnia) during artificial ventilation. Even
more surprising is the discovery by the inventor that moderate
hypercapnia will not cause hypoxia, provided sufficient oxygen
reaches the patient; in fact, moderate hypercapnia can be
beneficial to a patient (e.g., improve cardiovascular oxygen
availability and tissue oxygenation). In yet another aspect of the
present invention, the arterial blood carbon dioxide tension
(P.sub.aCO.sub.2) can be predictably controlled via a predetermined
dead space created in the unilimb device breathing tubes (i.e., the
volume in the outer tube defined by the space between the outer
tube distal end and the inner tube distal end). The dead space
volume may be made adjustable by use of axially extendable and
compressible corrugated tubing (which does not rebound to its prior
length and maintains its approximate internal diameter despite
bending and/or axial length changes); the tubing connects at its
proximal end to the patient port of the proximal terminal, and may
have dead space calibration markings thereon to permit
determination and adjustment of dead space volume contained
therein.
[0016] In another aspect, the present invention includes an
artificial ventilation method which avoids hypocapnia and hypoxia.
The method comprises provision of artificial ventilation to a
mammal (in which the mammal inspires and expires spontaneously or
with mechanical assistance) sufficient to prevent hypoxia, while
permitting a sufficient portion of the mammal's expiratory gases to
be rebreathed to allow the arterial carbon dioxide tension of the
mammal to be between about 35 mmHg to about 45 mmHg (i.e.,
normocapnia for a human). In another aspect, the mammal's
expiratory gases are rebreathed sufficiently to permit the arterial
carbon dioxide tension to be between about 45 mmHg to about 95 mmHg
(i.e., moderate hypercapnia). This surprising invention includes
new artificial ventilation tubing and/or filters, and methods for
providing same, which permits the user to provide sufficient
oxygenation and carbon dioxide to a patient, while using a minimum
amount of disposable, single-use materials.
[0017] Another aspect of the present invention includes an improved
unilimb device useful in providing the above artificial ventilation
method. In a preferred embodiment, a unilimb device for use in a
breathing circuit includes an outer tube, and an inner tube, each
having a proximal end and a distal end. The outer diameter of the
inner tube is smaller than the inner diameter of the outer tube,
wherein the outer tube can be operably connected at its distal end
to a fitting (e.g., endotracheal tube or mask) that can provide
artificial ventilation to a mammal. The inner tube is at least
partially disposed within the outer tube, and the distal end of the
inner tube is disposed within and in direct fluid communication
with the outer tube. The proximal end of one of the tubes is
connected to an inspiratory gas input (preferably the inner tube),
and the proximal end of the other tube is connected to an exhaust
outlet. The distal end of the inner tube is axially disposed at a
predetermined distance from the distal end of the outer tube to
create a dead space in the outer tube between the tube distal ends.
The dead space permits the mixing of inspiratory (fresh) gases with
expiratory gases from a patient operably connected to the device,
and thereby the amount of gases rebreathed by a patient can be
related to the dead space volume. This dead space can be
predetermined and adjusted to provide for normocapnia or moderate
hypercapnia while avoiding hypoxia. In a preferred embodiment, an
inner tube and outer tube are provided, which, when operably
connected to a mammal to provide respiration, the dead space
external of the patient is at least 10 cubic centimeters, and in
another preferred embodiment at least 30 cubic centimeters. This
dead space may be as small as 10 cubic centimeters for normocarbia
in a small mammal (e.g., a human infant), and may exceed 150 cubic
centimeters in larger mammals (e.g., adult humans).
[0018] As used herein, and as is conventionally understood, dead
space may also be defined as that volume in a patient respiratory
conduit external of a patient and distal of the most distal source
in or connected to the patient respiratory conduit of fresh
inspiratory gases to the patient, and includes the space in the
conduit(s) and devices external of the patient; for example, if a
single patient respiratory conduit carries inspiratory and
expiratory gases, dead space is the volume in the patient
respiratory conduit between the patient and the inspiratory gas
inlet, and any filters or other devices therebetween. If, for
example, a coaxial patient respiratory conduit is used (which, for
example, has an outer flexible conduit for carrying expiratory
gases from a patient operably connected to the distal end thereof),
and the inner flexible tube of the coaxial patient respiratory
conduit is connected to an inspiratory gas inlet, then the volume
in the patient respiratory conduit (and any fittings, filters and
other devices) between the patient and the distal end of inner
flexible tube is dead space.
[0019] Since it is desirable to have the assisted ventilation
system at a distance from the patient to permit health care
personnel better access to the patient, in one embodiment of the
present invention, the coaxial tubing is of considerable length,
and has little or substantially no dead space therein; the distal
end of the inner flexible tube is biased against or bonded to a
distal fitting connected to the end of the distal end of the outer
flexible tube. A dead space tube can be operably connected to the
distal end of the coaxial flexible tubing; in a preferred
embodiment, the dead space tube is connected to a distal fitting at
the end of the coaxial tubing. The dead space tube can be operably
connected through a filter (having a predetermined dead space
therein) at its proximal end to the distal fitting at the distal
end of the coaxial tubing (thus filtering both inspiratory and
expiratory gases), or the filter may be connected at the distal end
of the dead space tube. Thus, a coaxial flow of inspiratory and
expiratory gases may be directed through a single filter and dead
space tube.
[0020] In another embodiment, the inner tube of the coaxial conduit
is of a fixed length and preferably of a dark color (or has a dark
colored band about its distal end); the outer tube can have its
length adjusted, and is made of a clear (transparent or
semi-transparent) material. The dead space may be adjusted by axial
extension or contraction of the outer tube to alter the axial
distance between the distal end of the outer tube and the distal
end of the inner tube. The outer tube can be formed of a section of
corrugated tubing, such as for example FLEXITUBE.RTM., which upon
axial extension from its compressed axial conformation, or vice
versa, will retain its axial length (e.g., will not rebound; i.e.,
accordion-like pleated tubing). Further, the FLEXITUBE.RTM., when
bent, will retain the angle of curvature it is bent to without
substantial reduction in the tube's inner diameter. (Suitable
corrugated tubing for use in the present invention is used in the
Ultra-Flex circuit from King Systems Corporation, of Noblesville,
Ind., U.S.A.). The inner tube can be seen through the outer tube
and, in one embodiment, the dead space volume can be determined by
reference to calibration markings, which are on the outer tube,
aligned with the distal end of the inner tube. By placement of a
biological contamination filter between the distal ends of the
inner and outer tubes and the patient port of the proximal terminal
of the unilimb device, the current invention makes it possible to
safely extend the service life of the proximal terminal beyond a
single use. An example of suitable prior art biological
contamination filter means, which can be used in some embodiments
of the present invention, is the VIROBAC II Mini-Filter by King
Systems. Likewise, other adapters and a variety of single use
devices, previously connected at the distal or patient fittings,
can be reused by connection to the interface at the proximal side
of the biological contamination filter. Since the proximal terminal
is more complicated to manufacture, this invention permits
substantial cost savings by permitting reuse of the proximal
terminal and other devices connected thereto, while simultaneously
reducing environmental (medical) wastes.
[0021] In another embodiment, patient safety is enhanced by
provision of unique connector fittings for connecting components of
assisted ventilation systems, for example for connecting tubing and
filters. For example, a unique proximal connector fitting on a
filter matches and connects to a mating fitting on the distal end
of either a single or coaxial patient respiratory conduit. The
mating fitting on the distal end of a patient respiratory conduit
may be provided with a locking device to prevent accidental
disconnection. Further, patient respiratory conduits and proximal
terminals may also be provided with a blocking device to prevent an
unmatched dead space tube, filter, or other devices from being
connected thereto. Thus, for example, only filters meeting minimum
requirements can be connected to single or coaxial patient
respiratory conduit having a mating fitting. In addition to
filters, other devices may be provided with unique connector
fittings corresponding to the unique fittings on the distal end of
the patient respiratory conduit. In another embodiment of the
present invention, an adaptor is provided, in which the distal end
has a standard patient device connector to accommodate standard
filters and patient airway devices (e.g., endotracheal tube
proximal end), and the proximal end has a unique connector fitting
for a mating connector on the distal end of a patient respiratory
conduit.
[0022] In yet another aspect, the present invention includes a
system for use in mammals to provide respiratory and other gases.
The system comprises a first breathing conduit having a proximal
end and a distal end for providing and exhausting respiratory gases
from a mammal, and an interface comprising a breathing circuit
operably connected to the proximal end of the first breathing
conduit. A biological contamination filter blocks biological
contaminants in the first breathing conduit from communicating with
the interface components while allowing for adequate transmission
of inspiratory and expiratory flows.
[0023] The biological contamination filter can be located within
the proximal end of the first breathing conduit, or serve as a
separate detachable component. In one embodiment of the present
invention, a coaxial filter apparatus is provided. The filter
apparatus comprises an inner housing having openings at its
opposite ends; at least one of the openings has an internal
diameter which equals the internal diameter of the inner tube of
the breathing conduit, so that the filter device may be attached in
a coaxial fashion with the inner tube of the breathing conduit. The
inner diameter of the filter device inner housing expands to form a
chamber which accommodates a filter having a predetermined diameter
to permit sufficient flow therethrough (i.e., flow resistance is
inversely proportional to filter surface area). The inner housing
is contained within, and in spaced parallel relationship with, an
outer housing which is similar or identical in shape, but of
sufficiently greater internal diameter throughout to permit fluid
to flow between the outer walls of the inner housing and the inner
walls of the outer housing. A single disc shaped filter may be
contained within the inner housing and radially extend from within
the inner housing chamber to the outer housing chamber, or a filter
in the shape of an annular ring may be disposed about the outer
diameter of the inner housing filter chamber and extend to the
inner wall of the outer housing chamber. The inner and outer filter
housings may each be constructed from two funnel shaped components,
a pre-filtration housing and postfiltration housing (which are
mirror images of each other); the two components can be assembled
together after placing a filter therebetween at the center of the
filter chambers to be formed thereby.
[0024] A preferred embodiment of the proximal terminal interface
comprises a T-shaped housing, having an inspiratory gas input
(inspiratory port), an expiratory gas outlet (expiratory port), and
a first respiratory (patient) port. The first respiratory port can
be placed in fluid communication, through the biological
contamination filter, with a first breathing (respiratory) conduit
leading to a patient. The inspiratory port of the proximal terminal
connects to and is integral with an internal conduit, which passes
through the housing of the proximal terminal, so that the distal
end of the internal conduit forms a second respiratory port, which
terminates within the first respiratory port. The second
respiratory port has a smaller diameter than the first respiratory
port, so that gases may flow through the first respiratory port and
through the space between the exterior wall of the inner conduit
and the interior wall of the proximal terminal housing. The new
proximal terminal of the present invention permits the ready
connection and disconnection of an inner tube of a coaxial
respiratory conduit to the inspiratory gas source, since direct
sealed fluid communication with the inspiratory port is greatly
facilitated by the inner conduit of the new proximal terminal
housing. Thus, the prior art difficulties with connection of the
inner tube of unilimb devices to the inspiratory port are
eliminated, making it possible to avoid sealably bonding the inner
flexible respiratory tube to the inspiratory port of the proximal
terminal during manufacture.
[0025] It is noted that in preferred embodiments of unilimb
ventilation devices, the inner tube carries inspiratory gases from
an inspiratory gas source, and the outer tube carries expiratory
gases. Generally, it is desired that inspiratory gas flow be
laminar, while the expiratory gas flow should be turbulent.
Turbulent expiratory gas flow is facilitated by the annular shape
of the passage between the inner wall of the outer tube and outer
wall of the inner tube, as well as by the confluence of gases
exiting from the inner tube distal end into the dead space with
expiratory air. Further, filtration of the expiratory gases
increases turbulent flow in the outer tube, causing a positive end
expiratory pressure (PEEP) effect, which helps to maintain positive
pressure in the patient airway (to prevent atelectasis). Thus, the
coaxial filter apparatus of one embodiment of the present invention
helps create turbulent flow in the expiratory gases, when the outer
tube is used as the expiratory gas conduit.
[0026] In one embodiment, the first breathing or respiratory
conduit includes one tube, referred to herein for simplicity as the
outer tube, and has a first (proximal) end and a second (distal)
end. The outer tube is connected at its first end through a filter
device to the first respiratory port, and has its second, or
distal, end directed toward the patient. Both the first and second
respiratory ports terminate in and are in fluid communication with
the proximal end of the outer tube through one or more biological
filters. Thus the first breathing conduit between the patient and
the proximal terminal can comprise a single tube, the entire length
of which provides a dead space, or mixing chamber for inspiratory
and expiratory gases. The first breathing conduit is detachable
from the proximal terminal for disposal or sterilization. Use of
this system reduces costs and waste, since only the breathing
conduit is designed for single use. Another advantage is that the
proximal terminal of prior art unilimb devices, such as the
UNIVERSAL F.TM., is no longer disposed of after a single use, and
may be a permanent part of the interface.
[0027] In one embodiment of the present invention, the respiratory
conduit may comprise an outer flexible tube, the length of which
can be preselected from various lengths to vary the dead space to a
preselected volume. In another embodiment, the outer tube can be
axially expandable and compressible (i.e., have accordion-like
pleats) to make the dead space adjustable; the dead space can be
determined by reference to calibration markings on the outer tube.
The calibration markings on the pleated tube may be concealed in
the folded pleats, and revealed in opened pleats. The calibration
markings may be color-coded bands.
[0028] In another aspect of the present invention, the first
breathing conduit further comprises an inner flexible tube axially
disposed within the outer flexible tube. The inner tube proximal
end is connected through a biological contamination filter to the
second respiratory port, and the distal end of the inner tube
terminates inside of the outer tube. The dead space can be adjusted
by adjusting the axial distance between the outer tube distal end
and inner tube distal end. In one embodiment, the proximal end of
the flexible inner tube and the proximal end of the flexible outer
tube are held in spaced parallel coaxial relationship by a rigid
fitting, formed of coaxial rigid annuli, a smaller annulus within a
larger annulus, which are held in fixed spaced relationship by
rigid radial struts extending from the exterior of the inner
annulus to the interior of the outer annulus; in one embodiment,
the struts do not extend to the ends of the inner annulus to permit
a flexible conduit to be connected thereover. In a preferred
embodiment, the fitting connects to the distal end of a filter
device, which has a threaded or flanged connector at its proximal
end to permit secure attachment to, and simple detachment from, the
first and second respiratory ports. In a preferred embodiment, the
internal conduit of the interface proximal terminal carries
inspiratory gases to the second respiratory port, and the outer
tube of the interface carries expiratory gases entering from the
first respiratory port. The inner and outer tubes may be of
predetermined lengths to provide a predetermined dead space, or the
outer tube may be of variable length to permit adjustment of the
dead space (or an extension added to the outer tube, with the
extension having a fixed or adjustable volume or dead space);
calibration markings on a clear outer tube may be aligned with the
end of the inner tube to determine dead space volume.
[0029] The provision of readily accessible first and second
respiratory ports in the distal end of the proximal terminal
permits biological isolation of the first breathing conduit,
whether it comprises only an outer tube connected to the first
respiratory port, or a coaxial outer tube and inner tube, which are
connected to the first and second respiratory ports, respectively.
Thus, only the filter and first breathing conduit need be disposed
of (or sterilized) after a single use. The new interface of the
present invention permits numerous monitoring and control devices
to be included in the interface at the proximal end of the
biological filter(s). Various devices contained in detachable
modules can be repeatedly utilized with the interface, including
devices which were formerly attached to the patient nozzle and
disposed of after a single-use. Thus, the new assisted ventilation
system of the present invention provides for greatly simplified
construction of disposable unilimb single use components, which
reduces costs of production and at the same time reduces the
quantity of materials requiring replacement after a single use.
Further, fewer devices need be crowded about the patient, providing
improved surgical safety (less clutter at the patient makes for
easier surgical access and safety). Insertion of monitoring and
control devices at the proximal, post filtration, end of the
breathing system, permits improved control and monitoring of the
patients' respiration with a simpler device.
[0030] Therefore, the present invention provides a simpler
artificial ventilation system, that is easier and less expensive to
construct than prior art systems, is easier, safer and less
expensive to use, yet provides improved features. Further, the
present invention makes possible safer artificial ventilation by
providing means and a method for simultaneously preventing hypoxia
and hypocapnia. Further details and advantages of the present
invention will be appreciated by reference to the figures and
description of exemplary embodiments set forth herein.
DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a plan and partial cross sectional view of a prior
art assisted ventilation system utilizing a unilimb inspiratory and
expiratory gas conduit;
[0032] FIG. 2 is a cross-sectional view of a Fukunaga unilimb
inspiratory and expiratory gas conduit and proximal terminal as
described in detail in U.S. Pat. No. 4,265,235;
[0033] FIG. 3A is a cross-sectional perspective view of the new
proximal terminal of the present invention, which includes an inner
conduit connected to a second respiratory port;
[0034] FIG. 3B is a cross-sectional perspective view of an
alternative embodiment of the new proximal terminal illustrated in
FIG. 3A;
[0035] FIG. 4 is an exploded plan view of an assisted ventilation
system, with optional components, in accordance with the present
invention, including an interface and patient breathing
conduits;
[0036] FIG. 5A is a cross-sectional view of an embodiment of a
detachable patient coaxial breathing conduit for use in an assisted
ventilation system in accordance with the present invention, such
as the system of FIG. 4;
[0037] FIG. 5B is a cross-sectional view of an alternative
embodiment of the detachable patient coaxial breathing conduit
illustrated in FIG. 5A which includes a proximal extension;
[0038] FIG. 6A illustrates a perspective, partial cross-sectional
view of an embodiment of a coaxial filter device for use in an
assisted ventilation system in accordance with the present
invention;
[0039] FIG. 6B is a perspective, partial cross-sectional view of an
alternative embodiment of the coaxial filter device illustrated in
FIG. 6A;
[0040] FIG. 7 is a graphic illustration of the relationship between
dead space volume, V.sub.D, and the resulting change in patient
arterial carbon dioxide tension, P.sub.aCO.sub.2, including a
linear regression analysis curve, yielding a correlation
coefficient, r, of 0.671, and a predicted value for the change in
P.sub.aCO.sub.2 equal to the product of 2.621 times the V.sub.D,
added to 1.766; this graph illustrates that the change in
P.sub.aCO.sub.2 can be reliably predicted as a function of V.sub.D
(when V.sub.D is between 0 and 8 ml per kg of patient weight, or
cc.sup.3/kg);
[0041] FIG. 8 is a graphic illustration of the independence of
P.sub.aO.sub.2 as V.sub.D was varied between about 0 and 8 ml/kg,
including a linear regression analysis curve which shows no
significant correlation between the two variables in the range
tested;
[0042] FIG. 9 is a graphic illustration of the independence of
changes in P.sub.aCO.sub.2 and P.sub.aO.sub.2 as P.sub.aCO.sub.2
was varied between 0 and 25 mmHg, including a linear regression
analysis curve having a correlation coefficient, r, of 0.153, thus
showing that increasing P.sub.aCO.sub.2 between 0 and 25 mmHg has
no significant effect on P.sub.aO.sub.2;
[0043] FIG. 10 is a table for estimating the increase in arterial
blood carbon dioxide tension in relation to rebreathing circuit
apparatus dead space;
[0044] FIG. 11 is a plan view of an assisted ventilation system
using a prior art dual hose fitting connected through a filter to a
single patient conduit;
[0045] FIG. 12 is a partial cross-sectional view of the new
proximal terminal illustrated in FIG. 3A connected to the
detachable patient coaxial breathing conduit illustrated in FIG.
5A, which in turn is connected to a filter and a dead space
tube;
[0046] FIG. 13 is a plan view of a dead space tube connected to a
filter;
[0047] FIG. 14 is a plan view of an alternative embodiment of the
device of FIG. 13 which includes a connector fitting at its
proximal end;
[0048] FIG. 15 is an end elevation view of a distal connector
fitting for use in alternative embodiments of the present
invention;
[0049] FIG. 16 is a perspective end elevation view of an adapter
for use with the distal connector fitting of FIG. 15;
[0050] FIG. 17 is a plan view of an assisted ventilation system
using a prior art dual hose fitting connected at its proximal ends
to two filters and at its distal end to a single patient
conduit;
[0051] FIG. 18 is a plan view of an assisted ventilation system
using a prior art dual hose fitting connected to a single patient
conduit at its distal end, and having a filter connected at the
distal end of the single patient conduit;
[0052] FIG. 19 is an exploded partial cross sectional partial plan
view of a threaded adapter and the distal end of conduit including
a mating threaded connector fitting;
[0053] FIG. 20 is partial cross-sectional view of the new proximal
terminal illustrated in FIG. 3A connected to a detachable dead
space tube;
[0054] FIG. 21 is partial cross-sectional view of the new proximal
terminal illustrated in FIG. 3A connected to a detachable dead
space tube which in turn is connected to a filter; and
[0055] FIG. 22 is partial cross-sectional view of the new proximal
terminal illustrated in FIG. 3A connected to a filter which in turn
is connected to a detachable dead space tube.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0056] A brief description of a basic prior art artificial
ventilation system and unilimb device will facilitate a description
of the present invention. With reference to FIG. 1, a schematic
view of a circle circuit artificial ventilation system utilizing a
unilimb respiratory (inspiratory and expiratory) gas conduit is
illustrated. A unilimb respiratory (or breathing) conduit 1 may be
attached at outlet 2 (otherwise referred to as a nozzle or distal
terminal) to a patient endotracheal tube or mask. Breathing conduit
1 is formed to include an outer tube 4 and an inner tube 5.
Directional arrows 7 show the preferred direction of gas flow
through the system; for example, expiratory air is carried away
from a patient through the annular spacing between inner tube 5 and
outer tube 4. Inspiratory gases are provided to inner tube 5 from a
gas source 8, passing through a unidirectional valve 9. Inner tube
5 penetrates the wall of proximal terminal housing 11; housing 11
essentially comprises a bend in outer tube 4, and the outer wall of
tube 5 may be integrally sealed thereto.
[0057] A carbon dioxide absorber 13 may be used to remove carbon
dioxide from expiratory gases passed therethrough, and the
thus-filtered gases combined with inspiratory fresh gases from
source 8. Expiratory gases pass from a patient outlet 2 through
outer tube 4, then through unidirectional valve 15 to be
recirculated or vented at exhaust port 17.
[0058] With reference to FIG. 2, a Fukunaga unilimb device, such as
that described in detail in U.S. Pat. No. 4,265,235 is illustrated.
The device comprises a T-shaped proximal terminal 20, a distal
terminal 30, a flexible inner tube 40, and a flexible outer tube
50. Since the diameter of inner tube 40 is smaller than the
diameter of outer tube 50, an annular space 41 is formed
therebetween. The distal end 51 of outer tube 50 is connected to
distal terminal 30, which has means 31 for preventing the distal
end 42 of inner tube 40 from extending beyond distal terminal 30.
The distal end 42 of inner tube 40 is free of terminal 30 and outer
tube 50.
[0059] The T-shaped housing of proximal terminal 20 includes an
inspiratory port 22, an expiratory port 24, and a patient port 26.
Inner tube 40 is connected at its proximal end to inspiratory port
22, and passes partially through proximal terminal 20 and out of
patient port 26. In practice, the remote location of inspiratory
port 22 from patient port 26 makes it desirable to sealably bond
the proximal end 28 of inner tube 40 to inspiratory port 22, or,
optionally, a continuous length of inner tube 40 extends proximally
of inspiratory port 22, and distally of patient port 26 to at or
near distal end 51 of outer tube 50 (inner tube 40 acting to seal,
or being sealably bonded to, inspiratory port 22 at the point of
intersection therewith). Likewise, in order to reduce the risk that
the inner tube 40 might be dislodged from inspiratory port 22,
after being bonded thereto during manufacture, outer tube 50 is
bonded at its proximal end 52 to the outer wall 29 of patient port
26, and is bonded at its distal end 51 to distal terminal 30.
A New Proximal Terminal
[0060] With reference to FIG. 3A, a new and improved proximal
terminal 60 is illustrated, which has many surprising advantages
over prior art proximal terminals used in unilimb devices. Instead
of having three ports, like the proximal terminal 20 of FIG. 2,
proximal terminal 60 has four ports, which provide advantages and
features not possible with prior art artificial ventilation
systems. Proximal terminal 60 comprises a rigid, unitary T-shaped
housing, having an inspiratory port 62, an expiratory port 64, a
first respiratory port 66, and a second respiratory port 68.
Inspiratory port 62 has a step-wise taper from a wider-diameter
proximal end 63 to a narrow diameter distal end 65, although the
taper may be smooth and continuous, or have other shapes. An inner
conduit 70, having a proximal end 71 and a distal end 72 is
sealably connected and bonded to inspiratory port 62 at fitting 74
(due to the short distance between wider-diameter proximal end 63
and the narrow diameter distal end 65, and since the inner conduit
70 is bonded into inspiratory port 62, inspiratory port 62 is
considered as a single port for purposes of describing the
invention, rather than described as an external port at
wider-diameter proximal end 63 and as an internal port at the
narrow diameter distal end 65; thus, the proximal terminal 60 is
considered to have four ports if the inspiratory port is considered
as a single port, but may also be considered as having five ports
if the inspiratory port is considered as two ports). In a preferred
embodiment, the outer diameter of inner conduit 70 is sealably
bonded to distal end 65 of inspiratory port 62, so as to be
integral therewith. An integral annular wall 75 forms the distal
end 65 of inspiratory port 62. First respiratory port 66 and second
respiratory port 68 form concentric ports about axis line 78,
preferably having their concentric openings in the same plane which
is perpendicular to axis line 78 of inner conduit 70. Note that
second respiratory port 68, while shown axially centered or
concentric, within first respiratory port 66, may be off-center
with respect to axis line 78 (although this would require that at
least a portion of inner conduit 70 to likewise be off-center with
respect to axis line 78). In an alternative embodiment shown in
FIG. 3B, inner conduit 70 may axially extend outward slightly from
first respiratory port 66 so as to further facilitate connection of
a tube to second respiratory port 68. Optional flanges 76 may be
provided at second respiratory report 68 and/or first respiratory
port 66 in order to engage matching threads or flanges of
detachable tubular fittings which may be attached thereto
(additional embodiments of connecting fittings are further
described below with reference to FIGS. 14, 15, 16, and 19). If
flexible tubing is to be connected to first and second respiratory
ports by pressure fit or friction fit, the walls of the housing 60
should be sufficiently rigid to permit a firm sealed connection.
The new proximal terminal may be formed of rigid plastic, such as
is typically used in rigid attachments to artificial ventilation
systems. Since the new proximal terminal is designed for multi-use,
it may also be formed of metal, such as stainless steel. If the
terminal is formed of plastic (such as that used in the UNIVERSAL
F.TM. proximal terminal), it may be clear, translucent or opaque.
It is important that the walls of the proximal terminal housing
near and at the ports have sufficient rigidity to permit connection
to conduits, such as the patient respiratory conduit tubes, and
conduits connecting to the inspiratory and expiratory ports.
New Unilimb Artificial Ventilation System, Including New
Interface
[0061] With reference to FIG. 4, an exploded plan view of an
assisted ventilation system utilizing the new proximal terminal 60
of FIG. 3A is illustrated. In the embodiment of FIG. 4, a block
diagram of an interface 80 is shown. Proximal terminal 60 is
intended to be manufactured and shipped as a component independent
of flexible breathing or respiratory conduit(s) which would lead to
a patient, rather than being integrally bound (i.e., bonded) during
manufacture to flexible respiratory conduits as with prior art
unilimb devices. Therefore, it need not be disposed of or
sterilized after a single use, and it may be incorporated in a
single unit, such as interface 80, along with other functional
devices 81, 82, 83, and 84, which are illustrated here in block
diagram form for simplicity, or it can be placed before or after
interface 80 (i.e., the new proximal terminal may be a permanent
component of an assisted ventilation device or anesthesia machine).
The flexibility of new proximal terminal 60 is illustrated by
showing it in block form 60A. Although four functional devices
81-84 are incorporated in interface 80, more or less than this
number may be used. Functional devices may be in the form of
readily attachable and detachable modules, so that the ventilation
system may be easily modified to meet the requirements of the user.
Further, a varying number of optional functional devices, such as
devices 85, 86, 87, 88, and 89 may be incorporated in the system,
both proximal and distal of proximal terminal 60A.
[0062] In the embodiment of FIG. 4, a coaxial breathing conduit 100
(described in more detail below) is connected at its proximal end
to functional devices 85 and 86, which in turn are connected to
biological filter 90 (another embodiment of which is described in
detail below). Inspiratory and expiratory gases must pass through
filter 90, thus isolating interface 80, and other system components
connected proximally of filter 90, from contamination (infection)
by patient expiratory gases conducted by conduit 100.
[0063] In one embodiment devices 85 and 86 may comprise an O.sub.2
controller (for air dilution) and a CO.sub.2 controller (e.g., a
rebreathing shunt hole). A reservoir bag (useful during patient
transport and/or resuscitation) may be connected at, distal of, or
proximal of filter 90. If the coaxial respiratory conduit is used
for long term care, like in the ICU (intensive care unit and the
like), devices 85 and 86 may comprise a nebulizer and a water trap.
Devices 81-84, 87-89 may likewise perform control and/or monitoring
functions. For example, devices in modular form can be added so
that oxygen can be monitored by an oxygen sensor, and controlled by
an air dilution valve; carbon dioxide can be monitored by a
capnometer, and controlled by a rebreathing shunt hole; anesthetic
gases can be monitored by sensors and controlled by an anesthesia
machine; and temperature and humidity can be monitored by
appropriate devices, and controlled by an artificial nose.
A New Patient Respiratory Conduit
[0064] With reference to FIG. 5A, an alternative embodiment of a
patient breathing conduit for use with the proximal terminal of
FIG. 3A is illustrated. Breathing conduit 100 consists of a
flexible inner tube 110 and a flexible outer tube 120, both
connected to proximal fitting 130. Inner tube 110 and outer tube
120 are kept in spaced coaxial relationship at their proximal
connection to fitting 130. In one embodiment, inner tube 110 and
outer tube 120 are permanently bonded to fitting 130. Fitting 130
has radial flanges 132 which keep rigid inner pipe 134 connected to
but spaced from rigid outer pipe 136. Threads or flanges may be
optionally provided on inner pipe 134 and/or outer pipe 136 to
permit engagement with flanges or threads at second respiratory
port 68 and/or first respiratory port 66, or to permit connection
to a filter device, which in turn connects to second respiratory
port 68 and/or first respiratory port 66.
[0065] Distal end 122 of flexible outer tube 120 connects to a
rigid annular distal terminal 124. The distal end 112 of flexible
inner tube 110 does not axially extend beyond distal terminal 124
or the distal end 122 of outer tube 120. The distal end 112 of
flexible inner tube 110 may optionally be connected to distal
terminal 124 or to the distal end 122 of outer tube 120, or may be
free to move axially within outer tube 120. The distance between
distal end 112 of flexible inner tube 110 and the distal end 122 of
flexible outer tube 120 (as extended by distal terminal 124)
defines a dead space 138. In one embodiment of breathing conduit
100, varying lengths of flexible inner tube 110 and/or flexible
outer tube 120 are utilized in order to vary the size of the dead
space to a predetermined volume. In another embodiment, outer tube
120 is formed of adjustable-length tubing, so that the dead space
can be adjusted by extending or compressing the outer tubing axial
length. Extension may be done by adding a dead space tube to the
distal end of outer flexible tube 120, rather than or in addition
to using an extendable, accordion-like outer flexible tube. The
outer tubing may be formed of transparent or semi-transparent
material, and calibration markings 121 may be included thereon to
permit determination of dead space volume by alignment of the
distal end 112 of inner tube 110 with the markings 121.
[0066] Distal end 122 of flexible outer tube 120 or distal terminal
124 may be provided with a positioning device, which may be formed
of one or more inner tapered flanges, or a positioning ramp, with a
terminating stop, so that when the distal end 122 of flexible outer
tube 120 or distal terminal 124 is biased against the distal end
112 of inner flexible tube 110, the distal end 112 of flexible
inner tube 110 is positioned at the desired location with respect
to distal end 122 of flexible outer tube 120 or distal terminal
124, with the terminating stop preventing distal end 112 of
flexible inner tube 110 from extending distally of distal end 122
of flexible outer tube 120 or distal terminal 124.
[0067] In a preferred embodiment, flexible tubes 110 and 120 are
readily attachable to and detachable from fitting 130, and flexible
tube 120 is readily attachable to and detachable from distal
terminal 124. In one embodiment, flexible tube 110 is not utilized,
so that the entire length of tube 120 constitutes dead space. In
another embodiment, tube 110 and/or tube 120 connect directly to an
interface, which incorporates proximal terminal 60; a biological
filter is located between the proximal terminal and tubes 110 and
120.
A New Coaxial Filter
[0068] With reference to FIG. 6A, a preferred embodiment of a new
coaxial filter device 140 is illustrated, which can be used in a
unilimb ventilation device. Filter 140 includes an inner housing
150 and an outer housing 160. Inner housing 150 is formed of
tubular conduits 152 and 154 connected to opposed openings in
filter chamber 156, which contains a first or inner filter 158.
Outer housing 160 is formed of tubular conduits 162 and 164
connected to opposed openings in filter chamber 166, which contains
a second or outer filter 168. Flanges or threads may be provided at
one or more of the tubular conduit ends 153, 155, 163, and 165, so
that the filter may be secured in axial relationship to other
tubular fittings. In a preferred embodiment, filter device 140 is
connected to a proximal terminal, such as proximal terminal 60 in
FIG. 3A, so that inner tubular conduit 152 is sealably connected to
the second respiratory port 68 and outer tubular conduit 162 is
sealably connected to the first respiratory port 66. In a preferred
embodiment, inspiratory gases pass into tubular conduit 152, pass
through filter 158, and out of tubular conduit 154 into a breathing
conduit, such as breathing conduit 100 illustrated in FIG. 5A,
leading to a patient. Expiratory gases pass out of a breathing
conduit into the annular spacing between outer tubular conduit 164
and inner tubular conduit 154; the expiratory gases then pass
through filter 168, into tubular conduit 162 (i.e., the annular
spacing between outer tubular conduit 162 and inner tubular conduit
152), and into the proximal terminal and out of the expiratory port
of the proximal terminal, such as port 64 in proximal terminal 60
in FIG. 3A. The preceding gas flow pattern can be reversed if
desired.
[0069] In an alternative embodiment shown in FIG. 6B, filters 158
and 168 can be coplanar, and may even be formed of a single filter
disc passing from the inner wall of the outer filter chamber
through the wall of the inner filter chamber. In yet another
embodiment, inner tubular conduit 152 may axially extend from the
end 163 of tubular conduit 162; the extension of tubular conduit
152 is sufficiently long to reach and sealably connect to the
inspiratory port of a prior art proximal terminal, which lacks the
inner conduit of the new proximal terminal of the present
invention. An advantage of the coaxial filter is that one filter
device may be used rather than two, using less space in shipping,
use, and disposal.
[0070] With reference to FIG. 5B, an optional tubular extension 135
is illustrated which may be connected to end 137 of the inner pipe
134. Extension 135, when connected to end 137 is sufficiently long
to reach and sealably connect to the inspiratory port of a prior
art proximal terminal, which lacks the inner conduit of the new
proximal terminal of the present invention.
[0071] In a preferred embodiment, the patient, or respiratory,
conduit comprises a flexible tube with a diameter between 22 mm and
28 mm, and a length between 100 cm and 1.5 meters. If an inner tube
is used with the aforementioned tube, the diameter (or D) is
preferably between 11 mm and 15 mm. When using a single tube
respiratory conduit, a 22 mm diameter is desirable for adult use,
and a 15 mm diameter is desirable for pediatric use. When a coaxial
conduit is used, a 28 mm diameter outer tube and 15 mm diameter
inner tube are preferred. Single tube and coaxial respiratory
conduit conventionally have standard slip fittings at at least one
end for connection to other components to be used in an assisted
ventilation system.
[0072] Dead space volume, V.sub.D, in a tube is determined by the
relationship:
V.sub.D=.pi.(D/2).sup.2.times.L,
[0073] where L is the length of the dead space, and D is the outer
conduit tube diameter. In a preferred embodiment, the first (outer)
and second (inner) respiratory ports of the proximal terminal have
inner diameters which are approximately equal to that of the outer
tube and inner tube, respectively. Likewise, the outer and inner
conduits at the opposed ends of the coaxial filter have inner
diameters which are preferably approximately equal to that of the
outer tube and inner tube, respectively; and the outer and inner
annuli (i.e., ends of pipes) of the proximal fitting have inner
diameters which are preferably approximately equal to that of the
outer tube and inner tube, respectively.
[0074] Thus, the present inventor has described a new unilimb
artificial ventilation system, which includes a new patient
conduit, a new coaxial filter, and a new proximal terminal, the
latter of which may be incorporated into a new multifunctional
interface. Various advantages and features of these inventions will
be readily apparent to one of skill in the art; by way of
non-limiting examples, these new devices are less expensive to
manufacture; are easier to use; and have a wider range of uses and
configurations than prior art systems; these new devices reduce
medical wastes, since more components can be reused; yet, these
devices are safer to use, due to the reduction of equipment
required at the patient terminal, and provide for greater
monitoring and control.
Artificial Ventilation Which Avoids Hypoxia and Hypocapnia
[0075] The unilimb artificial ventilation device of the present
invention is ideal for providing artificial ventilation to a
patient in which hypoxia is avoided while safely avoiding
hypocapnia or even providing moderate hypercapnia. It was
surprisingly discovered that normal carbon dioxide levels
(normocapnia), or even moderate hypercapnia could be safely induced
and/or maintained in a patient without causing hypoxia, as
demonstrated by extensive data from human subjects, which
dramatically illustrates this surprising discovery, and how the
unilimb dead space volume can be adjusted to achieve normocapnia or
moderate hypercapnia without causing hypoxia.
EXPERIMENTAL
[0076] Traditional methods of artificial hyperventilation using
large tidal volume (V.sub.T>10 ml/kg) and ventilatory frequency
(f>10-12 breaths/min) inevitably result in a marked decrease in
arterial blood carbon dioxide tension (PaCO.sub.2), hypocapnia, and
is often associated with serious adverse side effects.
[0077] Adverse effects of hypocapnia include: a) Vital organ tissue
ischemia/hypoxia, since hypocapnia decreases cerebral, myocardial
and splanchnic blood flow, and shifts the oxygen dissociation curve
to the left, making the release of oxygen to the tissues difficult;
b) Hypocapnia causes reduction of cardiac output and thus decreases
the oxygen delivery (i.e. oxygen supply and availability to the
tissues); c) Hypocapnia causes severe vasoconstriction of some
tissues such as the skin; d) Hypocapnia causes blood and tissue
biochemical disturbances: Anaerobic metabolism increases blood
lactic acid concentration; and changes in plasma electrolytes
(sodium, potassium, calcium, etc.) cause cardiac arrhythmias,
metabolic acidosis, tetany, etc.
[0078] Therefore, studies were conducted to investigate the effects
of ventilation apparatus dead space (V.sub.D) on the arterial blood
carbon dioxide tension (P.sub.aCO.sub.2, "Pa" may be used
interchangeably with "Pa"), and oxygen tension (PaO.sub.2) during
anesthesia. After institutional approval and patient consent, a
total of 301 healthy (ASA class I) adult patients undergoing
elective surgery were studied (divided into Study I of 241
patients, and Study II of 60 patients). Anesthesia was induced with
a sleeping dose of thiopental; endotracheal (ET) intubation was
facilitated with 1 mg/kg succinylcholine. Anesthesia was maintained
with 60-70% nitrous oxide in oxygen and 0.5-1.0% halothane, or
0.8-1.5% enflurane, using a conventional anesthesia circle
breathing system with CO.sub.2 absorption. Intraoperative muscle
relaxation was achieved with intermittent pancuronium bromide as
required. The patients' lungs were mechanically ventilated using
the traditional mode of intermittent positive pressure ventilation
(IPPV) with the following ventilatory settings. Tidal volume
(V.sub.T=10 ml/kg), ventilatory frequency (f=10-12 breath/min), and
inspiratory/expiratory ratio (I:E ratio=1:2) were kept constant
throughout the study. V.sub.T was determined with a Wright
respirometer placed at the ET tube. Fraction of inspired oxygen
concentration (F.sub.iO.sub.2=0.3-0.4) was monitored using a
galvanic oxygen analyzer (Riken OX-160, Japan). End-tidal CO.sub.2
concentration was monitored using an infra-red CO.sub.2 analyzer
(AIKA, RAS-41, Japan).
[0079] After cardiopulmonary stabilization with the traditional
mode of ventilation (i.e. no dead space; i.e., dead space external
of the patient of less than 10 ml) was achieved, an arterial blood
sample from a radial artery was obtained and immediate analysis of
the blood sample was performed using an ABL2 blood gas analyzer
(Radiometer, Copenhagen) for control measurement. After control
values were taken, one or two of the predetermined dead space
volumes, V.sub.D, selected from 160, 200, 350, 510 and 550 (ml) was
(or were) chosen randomly, and incorporated in the breathing
circuit while the same artificial ventilation setting was
maintained for 30 min. Thereafter, blood gas measurements were
repeated for comparison and statistical analysis was performed. The
results of Study I of 241 patients are summarized in Table 1
(divided into Group A, 60 kg.+-.17; Group B, 65 kg.+-.9; and Group
C, 90 kg.+-.8), and results of Study II of 60 patients in FIGS.
7-10.
[0080] Table 1 shows that the traditional mode of artificial
ventilation using IPPV with no apparatus dead space inevitably
resulted in a marked decrease in arterial carbon dioxide tension
(PaCO.sub.2) i.e., hypocapnia. Addition of dead space,
V.sub.D=160-200 ml, V.sub.D=350 ml, and V.sub.D=550 ml,
significantly increased the PaCO.sub.2 to normocapnic and moderate
hypercapnic levels respectively, without evidence of substantial
PaO.sub.2 decreases, i.e. hypoxia, in any of the patients of Groups
A, B and C. Study II shows a mathematical regression analysis of
the blood gas data obtained from 60 patients (120 samples) during
artificial ventilation with varied dead space volumes. Thus, it is
demonstrated that a predetermined volume of dead space in the
breathing circuit can significantly control the PaCO.sub.2 values
without evidence of hypoxia during artificial ventilation, as
illustrated in FIGS. 7-10 and Table 1. Maintenance of normocapnic
levels may be highly desirable and beneficial to the patients
during anesthesia and/or to patients undergoing artificial
ventilation, for example in the ICU. As is clear from Table I and
FIG. 10, the vast majority of patients will require an assisted
ventilation system having a dead space of at least 100 cc, and in
many instances of at least 160 cc, to obtain normocapnia while
avoiding hypoxia, in accordance with the present invention.
1TABLE 1 Arterial Blood Gas Data Obtained From 241 Anesthetized
Patients (318 samples) During Artificial Ventilation With or
Without Apparatus Dead Space (Study I) Dead Space Volume (V.sub.D
in ml) Number of Body Weight Group Patients (Kg) 0 160-200 350 550
A 172 60 .+-. 17 Moderate Moderate B 61 65 .+-. 9 Hypocapnia
Normocapnia Hypercapnia Hypercapnia C 8 90 .+-. 13 Group FiO.sub.2
Control PaCO.sub.2 A (0.3) 32 .+-. 6 (mmHg) B (0.3) 33 .+-. 4 42
.+-. 9* C (0.3) 34 .+-. 7 46 .+-. 11* 51 .+-. 8* PaO.sub.2 A (0.3)
169 .+-. 40 (mmHg) B (0.3) 163 .+-. 28 164 .+-. 22 C (0.3) 178 .+-.
125 212 .+-. 116* 217 .+-. 137* Mean .+-. SD, *p < 0.05 vs
Control (V.sub.D = 0); Ventilatory setting: V.sub.T = 10 ml/kg, f =
10-12 breath/min, I:E ratio = 1:2.
[0081] FIG. 7 is a graphic illustration of the relationship between
dead space volume, V.sub.D, measured in milliliters per kilogram of
patient body weight (ml/kg, or cubic centimeters per kg of body
weight, cc.sup.3/kg), and the resulting change in patient arterial
carbon dioxide tension, P.sub.aCO.sub.2, (measured in mmHg),
including a linear regression analysis curve, yielding a
correlation coefficient, r, of 0.671, and a predicted value for the
change in P.sub.aCO.sub.2 equal to the product of 2.621 times the
V.sub.D, plus 1.766, or in equation form:
.DELTA.PaCO.sub.2(mmHg)=(2.621.times.V.sub.D (ml/kg))+1.766.
[0082] This illustrates that the change (.DELTA.) in
P.sub.aCO.sub.2 can be reliably predicted as a function of V.sub.D
(when V.sub.D is between 0 and 8 ml per kg of patient weight, or
cc.sup.3/kg).
[0083] FIG. 8 is a graphic illustration of the independence of
P.sub.aO.sub.2 as V.sub.D is varied between about 0 and 8 ml/kg,
including a linear regression analysis curve which shows no
significant correlation .RTM. is only 0.074) between the two
variables in the range tested. Thus, even when dead space volume is
large enough to increase P.sub.aCO.sub.2 by 15 mmHg (see FIG. 7),
there is no significant reduction in P.sub.aO.sub.2.
[0084] FIG. 9 is a graphic illustration of the independence of
changes in P.sub.aCO.sub.2 and P.sub.aO.sub.2 as P.sub.aCO.sub.2
was varied between 0 and 25 mmHg, including a linear regression
analysis curve having a correlation coefficient, r, of 0.153, thus
showing that increasing P.sub.aCO.sub.2 between 0 and 25 mmHg has
no significant effect on P.sub.aO.sub.2.
[0085] The table of FIG. 10 is generated by the results of data
shown in the graph of FIG. 7 of Study II.
[0086] Thus, the artificial ventilation method of the present
invention provides for increasing the dead space volume external to
a patient to induce and/or maintain normocapnia or moderate
hypercapnia while avoiding hypoxia. Without limiting the invention
to any particular theory of operation, it is believed that the
anatomical dead space present in a patient's respiratory system,
including for example that formed by the upper airway (i.e., nose,
mouth, laryngeal cavity), trachea and bronchial trees, is at least
partially eliminated by endotracheal intubation devices. Thus, the
amount of rebreathing from the anatomical dead space is reduced.
Further, in order to avoid hypoxia and atelectasis in the prior
art, inspiratory oxygen is provided at high pressure, large tidal
volume and rapid respiratory rate; this results in hyperventilation
and considerable reduction in concentration of arterial carbon
dioxide.
[0087] In a preferred embodiment, the dead space volume in a
unilimb patient respiratory conduit is adjusted to at least 10 ml
(cc.sup.3), or in an alternative embodiment to at least 30 ml, and
may be adjusted to or in excess of 150 ml. The unilimb patient
respiratory conduit used may be any of those described herein, or
modifications thereto. Although use of the devices described herein
is preferred for the foregoing artificial ventilation method, it is
anticipated that the discovery that increased carbon dioxide does
not necessarily cause hypoxia, so long as sufficient oxygen is
provided, may lead to the use of other devices to provide
artificial ventilation without hypocapnia or hypoxia. For example,
carbon dioxide from an external source may be combined with the
inspiratory gases, or a dual limb system may be used, in which
additional carbon dioxide is supplied to the patient. For example,
with reference to FIG. 11, a Y-shaped fitting 180 is illustrated,
which has an input port 182, an exhaust port 184, and a respiratory
port 186. Fitting 180 is connected at its distal end to a filter
device 190. One way valves, not shown, are proximal of ports 182
and 184 to ensure intermittent positive pressure ventilation. A
flexible tube 200 is attached at its proximal end 202 to the distal
end of filter device 190. Thus, the entire internal volume of tube
200 serves as dead space. The length and diameter of tube 200 may
be selected to achieve a predetermined dead space.
[0088] Thus, the assisted ventilation method of the current
invention, which avoids hypoxia and hypocapnia, can be provided in
some instances with older assisted ventilation systems, while still
having the advantages of a single tube for inspiratory and
expiratory gases. Tube 200 and filter device 190 may be sealably
bonded together, or separate easily attachable and detachable
components. Tube 200 can be of varying predetermined lengths of
uniform diameter for preselected dead space volume; tube 200 may
have axial adjustable length, and have calibration markings at its
opposed ends, the distance between the distal and proximal markings
thereon precalculated to provide a predetermined dead space (in one
embodiment, distal calibration markings can only be seen when the
surrounding flexible pleated tubing is axially extended, and are
not legible when the surrounding tube pleats are in their folded
axially compressed state).
[0089] In a preferred embodiment, artificial ventilation is
provided to a mammal (e.g., a human) sufficient to prevent hypoxia,
while a sufficient portion of the mammal's expiratory gases are
rebreathed to permit the arterial carbon dioxide tension of the
mammal to be between about 35 mmHg and about 95 mmHg, and, in
another preferred embodiment, the arterial carbon dioxide level of
the mammal is kept between about 35 mmHg and about 45 mmHg (i.e.,
normocapnia).
[0090] With reference to FIG. 12, an alternative embodiment of the
present invention is illustrated. Unilimb respiratory conduit 100
is connected at its proximal end to the distal end of proximal
terminal 60 via proximal fitting 130. Unilimb respiratory conduit
100 has a distal terminal 210, to which is connected outer flexible
tube 212 at its distal end 214. Inner flexible tube 216 is
connected at its proximal end to inner pipe 218 of proximal fitting
130. The distal end 220 of inner flexible tube 216 may be free to
move axially with respect to the distal end 214 of outer flexible
tube 212, or the distal end 220 of inner flexible tube 216 may be
connected to distal terminal 210, or the distal end 220 of inner
flexible tube 216 may be prevented from extending beyond the distal
end of outer flexible tube 212 (as possibly extended by distal
terminal 210) by a stop (not shown) in distal terminal 210.
[0091] Since the coaxial unilimb respiratory conduit 100 provides
the advantages mentioned above, and may have substantial length so
that it may reach from an assisted ventilation device located
remote from the patient, it is desirable in some instances to reuse
the coaxial unilimb respiratory conduit 100, or to add and/or
adjust the dead space independent of coaxial unilimb respiratory
conduit 100. Thus, filter 190 is detachably connected at its
proximal end 192 to distal terminal 210. Filter 190 is detachably
connected at its distal end 194 to proximal end 202 of flexible
tube 200. Flexible tube 200 may have a predetermined dead space, or
may have accordion-like folds therein to permit adjustment of the
dead space volume. In one embodiment, filter 190 is permanently
bonded to flexible tube 200, and the combination has a fixed dead
space (i.e., the volume of the filter and tube combined). In
another embodiment, calibration marks (such as 121 in FIG. 5A), can
be placed on flexible tube 200, and these calibration marks may
take into account the dead space volume of the filter (i.e., the
filter volume is added to the volume of flexible tube 200). Thus, a
user may dispose of filter 190 and tube 200 after a single use, and
referring to FIG. 13, a combination filter 190 and tube 200 for
single use is illustrated.
[0092] As is clear from the foregoing, in practice, a new assisted
ventilation device is made by health care personnel for each
patient from new disposable components in combination with reusable
components. The disposable components and reusable components
forming each assisted ventilation system are selected to match the
unique needs of each patient. Thus, the present invention provides
new components, new methods of providing components, and methods of
making assisted ventilation systems.
[0093] The filter and dead space tube combination is a surprisingly
valuable and useful device, as it was previously believed necessary
to minimize dead space, yet the dead space in the filter and tube
are intentionally made greater than what the inventors believe to
have previously been provided. The surprising discovery that dead
space can be used to achieve normocapnia or moderate hypercapnia
without hypoxia creates substantial patient health and cost
benefits. For example, by use of a filter and dead space tube in
connection with an assisted ventilation device (e.g., ventilator),
sufficient oxygenation can be provided to a patient while
maintaining a substantially normocapnic state with a single tube.
In certain instances, only the filter and the single tube (i.e.,
dead space tube) need be disposed of after use, thus creating
substantial cost savings, and reducing medical wastes. In a
preferred embodiment, the volume of the dead space in the dead
space tube and/or filter when connected between a patient and an
assisted ventilation device is sufficient to permit sufficient
oxygenation to a patient while maintaining a normocapnic or
moderate hypercapnic state. Preferably, the dead space volume in
the dead space tube and/or the filter is between about 10 cubic
centimeters and about 1000 cubic centimeters, and the flexible
tubing forming the dead space tube has a diameter between about 11
millimeters and about 28 millimeters, and a length between about 5
centimeters and 1.5 meters. In an alternative embodiment, the dead
space volume in the dead space tube and/or the filter is between
about 50 cubic centimeters and about 1000 cubic centimeters, and
the flexible tubing forming the dead space tube has a diameter
between about 15 millimeters and about 28 millimeters, and a length
between about 5 centimeters and 1.5 meters.
[0094] Thus, instead of requiring two tubes (one inspiratory and
the other expiratory), a single tube serves as both an inspiratory
and expiratory conduit. The present invention thereby creates a
surprisingly beneficial and new method of providing unilimb
respiratory conduits for use in providing assisted ventilation and
making assisted ventilation systems, wherein the systems are
constructed at the site of use by the user, users, and/or
assistants thereto, by use of tubing having a predetermined dead
space volume in the assisted ventilation system made for the
patient. In one embodiment, tubing of predetermined fixed volume,
or a range of volumes in the case of adjustable volume tubing
(e.g., FLEXITUBE.RTM.) is provided to the user. The user merely
needs to select a tube with the desired volume. In another
embodiment, tubing may be sold in coils of great length, and cut to
the desired size. Calibration marks may be made on the tubing to
permit easier determination of the volume in a length thereof. The
latter method is of course slower, and there is more room for human
error. Thus, it is believed that health care personnel will prefer
to use sections of tubing available at the site of use having
premeasured standard volumes, or volume ranges, and the sections of
tubing will preferably have either integral or attached fittings
thereon to facilitate fabrication of the assisted ventilation
system and operable connection to a patient.
[0095] In addition to providing new methods of making assisted
ventilation systems, the present invention includes tubing for use
in making assisted ventilation systems, of the new type described
herein having a dead space therein sufficient that when used to
provide assisted ventilation to a mammal maintains normocapnia or
moderate hypercapnia without hypoxia, wherein the tubing has the
length and diameter parameters needed to create the desired dead
space volume and/or range of volumes. Thus, also included in the
present invention are methods of providing tubing to users at the
site of use for use in making such assisted ventilation
systems.
COMPONENTS AND METHODS TO ENHANCE PATENT SAFETY
[0096] One of the objects of the present invention, and modern
medicine in general, is reducing biological and other types of
contamination, as frequently there are greater health effects to
patients from infection than from their underlying injuries.
Filters create a barrier to contamination from a patient and the
surroundings entering assisted ventilation devices, and likewise
create a barrier to any contamination in assisted ventilation
devices from being breathed in by patients. Nevertheless, it is
possible that in the rush and pressure of assisting patients, a
fresh filter will not be attached for each patient, or, in some
cases, filters not meeting minimum filtration standards will be
used. Further, while it may be desirable in some instances to reuse
the coaxial patient respiratory conduit by using the disposable
filter and dead space tube embodiment shown in FIGS. 12 and 13,
after a period of time, moisture, nebulized pharmaceutical agents,
and other chemicals may precipitate in the coaxial conduit, and/or
contaminants may build up therein. Thus, referring to FIG. 12, it
is desirable in some instances to ensure that coaxial unilimb
respiratory conduit 100 is disposed of after a single use along
with filter 190 and tube 200. In an alternative embodiment, a
coaxial filter, such as that illustrated in FIGS. 6A or 6B may be
inserted in the device of FIG. 12, wherein the proximal terminal 60
is separated from and operably connected to the coaxial unilimb
respiratory conduit 100 by the coaxial filter of FIG. 6A or 6B.
[0097] Thus, with reference to FIGS. 12, 14, 15, 16, and 19,
non-limiting examples of unique fittings are illustrated, which can
be utilized to ensure that proper connections are made to proper
devices, all with the design of maximizing patient well being,
while also minimizing costs. Referring back to FIG. 12, filter 190
is detachably connected at its proximal end 192 to distal terminal
210. The cylindrical proximal terminating portion or proximal
sleeve 193 of proximal end 192 has an inner diameter sized to
friction fit over the outer diameter of the distal terminating
portion or male fitting 211 of distal terminal 210. Either or both
of proximal sleeve 193 and male fitting 211 may be tapered to
facilitate connection therebetween; in another embodiment, the
proximal sleeve 193 (or female fitting) and male fitting 211 have
mating frustoconical shapes. By adjusting the size of proximal
sleeve 193 and male fitting 211, only components, such as dead
space tubes with predetermined specifications (or patient airway
devices, e.g., endotracheal tubes, laryngeal and other masks)
having the proper sized proximal sleeves may be connected to a
coaxial unilimb respiratory conduit such as that illustrated in
FIG. 12.
[0098] With reference to FIG. 14, an alternative embodiment of the
present invention is illustrated, in which filter 190 is integrally
connected to a proximal connector fitting 240. Filter 190 may also
be a combination filter and HME device (heat and humidity
exchanger). A partial cross section of cylindrical sleeve 242 is
shown to permit a side view of hooks 244 (all connector fitting
sleeves may be tapered or frustoconically shaped to facilitate
connection). Referring to FIG. 15, an end elevation view of a
distal connector fitting 250 for use in alternative embodiments of
the present invention is illustrated. It is envisioned that all
distal connectors may be used as proximal connectors and vice
versa, and thus, the distinction between distal and proximal
connector fittings is merely to facilitate description thereof. The
fitting 250 may be, by way of non-limiting examples, integrally
connected at the distal end of distal terminal 124 in FIG. 5A and
5B or distal terminal 210 in FIG. 12, or integrally connected at
the distal end of proximal terminal 60, for example in place of
flanges 76 on the distal end of the inner conduit 70, or may be
integrally connected to the distal end of the outer conduit in FIG.
3A.
[0099] A plurality of inwardly facing flanges 252 are provided to
block attempts to insert the ends of tubes or other devices, such
as inappropriate dead space tubes and/or filters, into distal
connector fitting 250. Thus, only devices which have a mating
fitting, such as for example proximal connector fitting 240, can be
connected to distal connector fitting 250.
[0100] With reference to FIG. 16, an adapter comprising proximal
connector fitting 240 is illustrated. Hooks 244 are annularly
arranged about and connected to inward facing annular flange 246. A
cylindrical sleeve 248 projects proximally from fitting 240, and
has an inner diameter which approximately matches the outer
diameter of distal connector fitting 250 (i.e., sleeve 248 and
connector fitting 250 are shaped and sized to permit sleeve 248 to
slidingly and sealably engage connector fitting 250). For example,
the proximal edge 249 of cylindrical sleeve 248 may be tapered out
to a larger diameter, and/or the distal edge 251 of distal
connector fitting 250 may be tapered inward to a smaller diameter
to facilitate a sealing slip connection of sleeve 248 over the
distal edge 251. An annular flange 254 is connected near or at
distal edge 251 in distal connector fitting 250 by tabs 256, thus
creating an annular pattern of openings 258 about the periphery of
annular flange 254.
[0101] Hooks 244 are formed of fingers 260 which project axially
and proximally from annular flange 246, and terminate in retaining
flanges 262. By axially aligning the proximal end of proximal
connector fitting 240 with the distal end of distal connector
fitting 250, hooks 244 may be aligned and inserted into openings
258. Counterclockwise rotation of fitting 240 with respect to
fitting 250 causes one or more retaining flanges 262 to be latched
behind one or more tabs 256, thus creating a more secure seal and
grip between the fittings. Optional barbs or teeth 264 are shown in
FIG. 16. In a preferred embodiment, when teeth 264 are used, the
length of fingers 260 is just sufficient to axially project the
retaining surface 265 of retaining flanges 262 so they may engage
the proximal surface of tabs 256 when fitting 250 is fully axially
inserted into fitting 240 and rotated. The teeth 264 have a tapered
surface 266 to create a ramp, and hooks 244 and annular flanges 246
and 254 are sufficiently resilient to permit the teeth to slide
over the proximal surface of tabs 256 upon relative
counterclockwise rotation of fittings 240 and 250 and to thereby
latch thereon. Each tooth has a locking surface 268, which permits
the tooth to snap into the opening immediately counterclockwise of
the opening in which its corresponding hook was inserted, which may
provide a tactile and/or audible indication that the two fittings
are fully engaged. Although hooks 244 are illustrated herein to
permit the engagement of teeth 264 with tabs 256 upon relative
counterclockwise rotation of fittings 240 and 250, the opposite
arrangement is also contemplated. The ability to releasably lock
fittings 240 and 250 together is dependant on the resilience of
hooks 244 and annular flanges 246 and 254, the length of teeth 264,
and the interaction of each locking surface 268 with the
corresponding surface on the tab to which it is engaged. Thus, in
one embodiment, teeth 264 serve to indicate that the fittings are
fully engaged, while in another embodiment, the teeth 264 prevent
the fittings 240 and 250 from being readily disconnected after the
teeth are locked in place.
[0102] With regard to FIG. 19, a male threaded fitting 280 and
female threaded fitting 290 are illustrated. In this alternative
embodiment, corresponding threaded fittings permit only matching
components to be attached. For example, threaded fitting 280 may be
integrally attached or bonded to the distal end of the inner
conduit 70 of proximal terminal 60. Only filters, tubing and/or
other devices have a mating threaded fitting 290 at the proximal
end thereof may be connected to threaded fitting 280.
[0103] As is apparent from the foregoing, manufacturers of filters,
patient airway devices (e.g., masks, endotracheal tubes, etc.),
HMEs, water traps, nebulizers, etc., provided they meet minimum
standards, may produce such devices with the appropriate fitting
240 or 250 integrally connected thereto, depending respectively if
it is to be connected to fitting 250 or 240, or analogously
fittings 280 and 290 or other appropriate matching fittings may be
used. In order to retrofit devices meeting minimum standards,
adaptors, such as that shown in FIG. 16, may be provided, which
have a mating connector at one end for the patient respiratory
conduit or other device to which they are to be connected, and
having a standard slip connector on the other end to attach to the
device to be retrofitted. In a preferred example, adapters, such as
shown in FIG. 16, have a first end 269 meeting international
standards and a second end meeting the particular fitting
requirements.
[0104] As is implicit and/or explicit from the foregoing, numerous
configurations of assisted ventilation systems are embodied in the
present invention. For example, with reference to FIG. 17, an
alternative embodiment of the present invention is illustrated
which uses a prior art dual hose fitting 310 connected at its
proximal ends to two filters 302 and 304 and at its distal end to a
single tube patient conduit 300. In view of the surprising
discovery that dead space contained within the single tube patient
conduit (along with whatever dead space exists in the dual hose
fitting and the other devices in the assisted ventilation system)
can be utilized to simultaneously prevent hypocarbia while
providing sufficient oxygenation, it is envisioned that single tube
patient conduits (also referred to herein as dead space tubes),
each having a predetermined dead space volume, or each having a
range of dead space volumes, will be provided as a separate
components. Note that due to the proximal placement of filters 302
and 304, both filters and all components distal thereof will be
contaminated by contact with a patient, and thus may require
disposal and/or sterilization after each use.
[0105] In accordance with the present invention, a method is
provided in one embodiment to cut tubing from a much longer length,
perhaps a roll or coil, to the desired length at the site of use to
achieve a desired dead space volume, or range of safe volumes in
the cases of pleated tubing (e.g., FLEXITUBE.RTM.). By having tubes
of predetermined volumes ready, there is less likelihood of a
mistake being made in cutting tubing to a desired length, and also
increases the safety and rate of making an assisted ventilation
device in accordance with the present invention.
[0106] FIG. 18 is a plan view of an assisted ventilation system
using a prior art dual hose fitting 310 connected to a single
patient conduit 312 at its distal end (dead space tube), and having
a filter 320 connected at the distal end of conduit 312. In this
embodiment, only one filter 320 is used, which may provide for less
waste, as it is possible, in certain instances, to only dispose of
filter 320 after use, without disposing of tube 312 and fitting
310. Dead space tube may also be referred to as a normocapnic (or
moderate hypercapnic) breathing tube, with it being understood that
such tubes in accordance with the present invention have a
predetermined volume, or range of volumes, sufficient to prevent
hypoxia when utilized to provide assisted ventilation while also
maintaining normocapnia or a desired level of carbon dioxide
rebreathing.
[0107] With reference to FIG. 20, proximal terminal 60, as
described in more detail above with reference to FIG. 3A is
connected to a single patient conduit 340. Thus, the entire volume
of conduit 340 is dead space. In this embodiment, proximal terminal
60 and conduit 340 are not protected by a filter. Thus, it is
anticipated that the embodiment of FIG. 20 would be used with a
filter 360, and/or with two separate filters attached to the
inspiratory gas inlet and expiratory gas outlet. FIG. 21 shows a
proximal terminal 60 connected to the proximal end of a patient
conduit 340 with a filter 360 connected to the distal end of
conduit 340. In the case shown in FIG. 20, it may be possible to
reuse proximal terminal 60 and conduit 340 by only attaching a
fresh filter 360. FIG. 22 shows a proximal terminal 60 connected to
the proximal end of a filter 360 with a patient conduit 340
connected to the distal end of filter 360. In the case shown in
FIG. 21, it may be possible to reuse proximal terminal 60 by
attaching a fresh filter 360.
[0108] Because of the features of proximal terminal 60, in one
embodiment, proximal terminal 60 forms part of, and is integral
with, the reusable components of an anesthesia machine and/or
assisted ventilation device. When proximal terminal 60 forms part
of, and is integral with, the reusable components of an anesthesia
machine and/or assisted ventilation device, it is preferably
provided with means for preventing connection thereto without
proper filtration means. Thus, unique connector fittings, such as
those illustrated in FIGS. 15, 16 and 19 may be utilized. In a
preferred embodiment, all components, including at least one
filter, operably attached to proximal terminal 60 are disposable
and lockingly engaged together, thus ensuring that patient safety
is maximized by requiring disposal of all of the disposable
components together after a single use. For example, by providing
proximal terminal 60 with a unique distal connector, only a proper
filter, having a mating proximal connector, can be attached
thereto. Likewise, the filter is provided with a unique distal
connector, which permits only permanent locking engagement with
single use tubing and/or devices leading to the patient. After use,
the filter and components connected thereto are disposed of, since
the permanent locking engagement of the components prevents
disengagement thereof without damage thereto. Proximal terminal 60
can have other shapes than that illustrated herein. For example,
additional ports and conduits can be added thereto, the shape of
the housing altered, and the location of ports and conduits
connected thereto altered.
[0109] While preferred embodiments of the invention have been
illustrated and described in detail in the figures and foregoing
description, the same is to be considered as illustrative and not
restrictive in character. For example, while tubes of circular
cross-section are used herein, it is anticipated that tubular
conduits of varying cross-sectional shape may be used, and that the
inner tube of a coaxial tube may or may not be axially centered
within the outer tube, or only portions of the inner tube may be
axially centered in the outer tube while other portions may be off
center. It is also envisioned that the proximal terminal may have
more than two conduits passing therethrough, which may connect to a
flexible respiratory conduit having more than two lumens. In place
of the push, twist and lock fittings of the present invention,
spring biased clips may be provided on the distal end of one
component, which snap onto corresponding tabs on the proximal end
of another component, or vice versa (the tabs and/or clips may have
tapered surfaces so that, when pressed against each other, the
clips will bend in order to receive the tabs). Thus, it is
understood that only the preferred embodiments have been shown and
described, and that all changes and modifications that come within
the spirit of the invention are desired to be protected.
* * * * *