U.S. patent application number 12/883331 was filed with the patent office on 2011-01-06 for surgical instrument and method for use thereof.
This patent application is currently assigned to THE REGENTS OF THE UNIVERSITY OF MICHIGAN. Invention is credited to Arnold Advincula, Robert Dodde, James Geiger, Kevin Pipe, William Roberts, Albert J. Shih.
Application Number | 20110004204 12/883331 |
Document ID | / |
Family ID | 38309948 |
Filed Date | 2011-01-06 |
United States Patent
Application |
20110004204 |
Kind Code |
A1 |
Dodde; Robert ; et
al. |
January 6, 2011 |
Surgical Instrument and Method for Use Thereof
Abstract
A surgical instrument for treating a tissue includes a handpiece
and a tissue engaging portion arranged to be received by the
handpiece. The tissue engaging portion includes first and second
opposed jaw members having an open position and a closed position
for engaging the tissue therebetween, where the first and second
jaw members are arranged to receive surgical energy from a surgical
generator. The tissue engaging portion further includes at least
one cooling member spaced from at least one of the first and second
jaw members, where the cooling member has an open position and a
closed position for engaging the tissue. Positioning the jaw
members in their closed position and applying surgical energy to
the tissue allows for treatment of the tissue, and positioning the
cooling member in its closed position provides at least one of a
pressure gradient or a thermal gradient between the jaw members and
the cooling member.
Inventors: |
Dodde; Robert; (Ann Arbor,
MI) ; Shih; Albert J.; (Ann Arbor, MI) ;
Geiger; James; (Ann Arbor, MI) ; Roberts;
William; (Saline, MI) ; Pipe; Kevin; (Ann
Arbor, MI) ; Advincula; Arnold; (Ann Arbor,
MI) |
Correspondence
Address: |
BROOKS KUSHMAN P.C.
1000 TOWN CENTER, TWENTY-SECOND FLOOR
SOUTHFIELD
MI
48075
US
|
Assignee: |
THE REGENTS OF THE UNIVERSITY OF
MICHIGAN
Ann Arbor
MI
|
Family ID: |
38309948 |
Appl. No.: |
12/883331 |
Filed: |
September 16, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11626812 |
Jan 24, 2007 |
7815641 |
|
|
12883331 |
|
|
|
|
60761901 |
Jan 25, 2006 |
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Current U.S.
Class: |
606/21 |
Current CPC
Class: |
A61B 18/1445 20130101;
A61B 2018/00047 20130101; A61B 2018/00023 20130101; A61B 2018/00011
20130101 |
Class at
Publication: |
606/21 |
International
Class: |
A61B 18/02 20060101
A61B018/02 |
Claims
1. A surgical instrument for treating a tissue, comprising: a
handpiece; and first and second opposed, electrically conductive
cooling members having an open position and a closed position for
engaging the tissue therebetween, the first and second cooling
members containing a coolant and arranged to receive surgical
energy from a surgical generator, wherein positioning the cooling
members in their closed position and applying surgical energy to
the tissue allows for treatment of the tissue, and activating the
coolant decreases the temperature of the tissue.
2. The surgical instrument according to claim 1, wherein the
cooling members have an arm-like configuration.
3. The surgical instrument according to claim 1, wherein the
cooling members have a U-shaped configuration.
4. The surgical instrument according to claim 1, wherein the first
cooling member comprises a first electrode and the second cooling
member comprises a second electrode of opposite polarity from the
first electrode.
5. The surgical instrument according to claim 1, further comprising
a first actuator operably connected to the first and second cooling
members for effecting movement thereof.
6. The surgical instrument according to claim 1, further comprising
a pump in communication with the first and second cooling members
for circulating the coolant therethrough.
7. The surgical instrument according to claim 1, wherein the first
and second cooling members comprise a heat pipe.
8. The surgical instrument according to claim 1, wherein the first
and second cooling members impart a Peltier effect.
9. The surgical instrument according to claim 1, further comprising
at least one temperature sensor provided on the first and second
cooling members.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 11/626,812 filed Jan. 24, 2007 which, in turn, claims the
benefit of U.S. provisional Application Ser. No. 60/761,901 filed
Jan. 25, 2006, the disclosure(s) of which are incorporated in their
entirety by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a surgical instrument, such as an
energy based surgical device.
[0004] 2. Background Art
[0005] Energy-based surgical devices (EBSDs),which use a variety of
energy sources (electrical, radio frequency, and ultrasonic), have
been adopted widely for nearly all types of surgery due to their
ability to effectively and rapidly control bleeding EBSDs have been
adopted widely for nearly all types of surgery including
neurosurgery, orthopedics, gynecology, urology, general surgery,
thoracic surgery, plastic surgery, and otolaryngology. Despite
their advantages, the success of EBSDs has been tempered by the
recognition that these devices can lead to collateral tissue damage
due to thermal and/or electrical spread outward from the
instrument.
[0006] For example, electrosurgery (monopolar and bipolar) involves
the use of alternating current in the radio frequency (RF) range to
generate heat for cutting and coagulating tissue. In bipolar
electrosurgery, opposed grasping members are used to clamp tissue
therebetween for coagulation, wherein the grasping members comprise
electrodes of opposite polarity. As electrical energy passing
through the tissue is transformed into heat, the tissue is
desiccated and the loss of water produces an increased electrical
resistance. As a result, surrounding tissue becomes relatively less
resistive to electrical current and the current's pathway will
switch course, resulting in a spread of thermal energy to tissue
outside of the grasping members. This makes predicting the route
current will take very difficult and not intuitive, and may lead to
unintentionally damaging nearby tissue.
[0007] In addition, medical personnel may not always be able to
visualize the thermal spreading because of obstructing tissue
structures, especially during an endoscopic procedure. The limited
field of view and narrow focus on a small area may allow thermal
spread to occur unnoticed, potentially causing damage to vital
structures. When performing electrosurgery or ultrasurgery in a
laparoscopic environment, the presence of an insufflating gas
having a low heat capacity may result in instruments not cooling as
rapidly, which may further increase the potential for thermal
damage.
[0008] Therefore, it is desirable to control the thermal spread
from EBSDs in order to minimize unwanted thermal damage to
surrounding tissues during surgical procedures as well as reduce
patient recovery times and post-operative complications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a perspective view of a surgical instrument system
according to an aspect of the present invention;
[0010] FIG. 2 is a perspective view of a tissue engaging portion of
a surgical instrument according to an aspect of the present
invention;
[0011] FIG. 3 is a perspective view of a smooth electrode
configuration according to one aspect of the present invention;
[0012] FIG. 4 is a perspective view of a toothed electrode
configuration according to another aspect of the present
invention;
[0013] FIG. 5 is a perspective view of a hybrid electrode
configuration having both smooth areas and toothed areas according
to another aspect of the present invention;
[0014] FIG. 6 is a perspective view of a tissue engaging portion
wherein cooling members serve as electrodes according to an aspect
of the present invention;
[0015] FIG. 7 is a perspective view of a tissue engaging portion
which includes temperature sensors according to an aspect of the
present invention;
[0016] FIG. 8 is a schematic diagram of an experimental set-up
wherein a cooling tube was placed adjacent the jaw members and
temperatures recorded at different distances from the edge of the
jaw members;
[0017] FIG. 9 is a graph depicting the experimental results using a
cooling tube with and without coolant;
[0018] FIG. 10 is an illustration of an example of the experimental
control group in which a cooling tube was not used;
[0019] FIG. 11 is an illustration of an example of the experimental
group in which a cooling tube was placed but did not contain
coolant;
[0020] FIG. 12 is an illustration of an example of the experimental
group in which a cooling tube was placed and contained coolant;
and
[0021] FIG. 13 is a schematic representation of a control system
according to an aspect of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] As required, detailed embodiments of the present invention
are disclosed herein; however, it is to be understood that the
disclosed embodiments are merely exemplary of the invention that
may be embodied in various and alternative forms. The figures are
not necessarily to scale, some features may be exaggerated or
minimized to show details of particular components. Therefore,
specific structural and functional details disclosed herein are not
to be interpreted as limiting, but merely as a representative basis
for teaching one skilled in the art to variously employ the present
invention.
[0023] The present invention includes a surgical instrument and
method for use thereof for controlling, minimizing, and monitoring
the spread of thermal energy during any type of surgery. In
accordance with the present invention, thermal and/or pressure
gradients may be created in the treated tissue to alleviate thermal
spread.
[0024] A perspective view of a surgical instrument system according
to the present invention is shown in FIG. 1 and designated
generally by reference numeral 10. System 10 includes a surgical
energy generator 12 such as, but not limited to, a monopolar
electrosurgical generator, a bipolar electrosurgical generator, or
an ultrasonic generator. Electrosurgical generators are
microprocessor-controlled electrical generators that deliver power
in the form of the necessary waveforms. Ultrasonic generators are
microprocessor-controlled and supply high frequency pulses of
alternating current to the handpiece, which in turn vibrates the
transducer. Monopolar devices include, for example, the
Surgistat.RTM. and Force FX generators manufactured by Valleylab
(Boulder, Colo.). Bipolar devices include, for example, the
LigaSure.TM. Vessel Sealing System from Valleylab and the PK.TM.
System from Gyrus Medical (Maple Grove, Minn.). Ultrasonic devices
include, for example, Harmonic Scalpel.RTM. by Ethicon
Endo-Surgery, Inc. (Cincinnati, Ohio), AutoSonix.RTM. by Tyco
Healthcare (Norwalk, Conn.), and SonoSurg.RTM. by Olympus Corp.
(Melville, N.Y.).
[0025] With continued reference to FIG. 1, system 10 according to
the present invention includes an energy based surgical instrument
14 comprising a tissue engaging portion 16 and a handpiece 18
arranged to removably receive portion 16. Handpiece 18 may have a
pistol-grip style as depicted herein, but is not limited to this
configuration. Tissue engaging portion 16 is arranged to be
connected to handpiece 18 both mechanically and electrically, and
cable 20 may be provided to connect instrument 14 to generator 12.
Activation of generator 12 may be performed from handpiece 18 or by
means of a footswitch unit (not shown) as is known in the art.
Surgical energy, such as electrosurgical or ultrasonic energy, may
then be conducted to instrument 14 and the tissue treated to a
desired degree.
[0026] Tissue engaging portion 16 may have a configuration as
depicted in FIG. 2, wherein portion 16 includes a first jaw member
22 and an opposed second jaw member 24 which are movable relative
to one another. Jaw members 22, 24 may be positioned in a spaced
apart, open position as shown in FIG. 2 for receiving tissue
therebetween, and jaw members 22, 24 may be positioned in a closed
position where jaw members 22, 24 are moved relatively closer to
one another in order to engage and treat the tissue therebetween.
Jaw members 22, 24 may have an arm-like configuration as depicted
in FIGS. 1 and 2. However, as shown in FIGS. 3-5, numerous
configurations of jaw members 22, 24 are contemplated according to
the present invention. Jaw members 22, 24 may have a U-shaped
configuration and could have smooth surfaces (FIG. 3), could have
toothed surfaces (FIG. 4), or could have a combination of smooth
and toothed surfaces (FIG. 5). It is understood that jaw members
22, 24 are not limited to the shape, size, and other configuration
depicted herein, and that any configuration of jaw members 22, 24
suitable for the intended purpose is fully contemplated.
Furthermore, instrument 14 may also include a cutting element if
desired.
[0027] Jaw members 22, 24 are arranged to receive surgical energy
from surgical generator 12. In the case of a bipolar
electrosurgical instrument, first jaw member 22 comprises a first
electrode and second jaw member 24 comprises a second electrode,
wherein the first and second electrodes have opposite polarity to
allow current to flow therebetween. The electrodes may be
constructed from a conductive material such as, but not limited to,
aluminum, stainless steel, platinum, silver, or gold. Although
instrument 14 may sometimes be described herein as being a bipolar
electrosurgical instrument, it is understood that embodying
instrument 14 as a monopolar electrosurgical device, ultrasonic
surgical device, or other energy based surgical device is fully
contemplated according to the present invention.
[0028] Instrument 14 may be used to dissect, grasp or clamp,
coagulate, and cut tissues during endoscopic, laparoscopic, and
open surgical procedures. Instrument 14 may be designed for single
patient use, or may be constructed to allow for sterilization and
use on more than one surgical patient.
[0029] As described above, during electrosurgical or ultrasonic
procedures, the thermal spread or dissipation of heat outside the
tissue area engaged by tissue engaging portion 16 may occur. As
best shown in FIG. 2, tissue engaging portion 16 may further
include at least one cooling member 30 spaced from at least one of
first jaw member 22 and second jaw member 24. In the configuration
depicted herein, one cooling member 30 is spaced from and generally
surrounding jaw member 22, and another cooling member 30 is spaced
from and generally surrounding jaw member 24. Cooling members 30
may each comprise a tube which may be U-shaped as depicted in FIG.
2. Of course, it is understood that other numbers and
configurations of cooling member 30 are fully contemplated. As with
jaw members 22, 24, cooling member(s) 30 are movable relative to
one another and may be positioned in an open position (FIG. 2) and
a closed position for engaging tissue. As heat is introduced into
the tissue by surgical instrument 14, cooling members 30 may
constrain the thermal spread by increasing the pressure and/or
temperature gradient in the heated region as described below.
[0030] Cooling members 30 may include a coolant such as water or
any other suitable liquid, chilled or unchilled, where the coolant
may be stationary or may be circulated within cooling members 30
(see, for example, arrows in FIG. 2) by a pump 32 (shown
schematically in FIG. 1) housed in handpiece 16 or elsewhere, or by
other means. In operation, as heat is generated at jaw members 22,
24, the coolant is also heated and that heat may be taken away from
the adjacent tissue by fluid flow toward handpiece 18. According to
an aspect of the present invention, cooling member 30 adjacent jaw
member 22 may have a different flow direction compared with cooling
member 30 adjacent jaw member 24. The coolant may be supplied
and/or circulated within cooling members 30 before, during, and/or
after the surgical procedure. Instead of a liquid such as water,
cooling member 30 could contain a gas coolant, such as carbon
dioxide. Still further, cooling member 30 could impart a Peltier
effect by supplying current to pull heat away from the tissue.
[0031] According to another aspect of the present invention,
cooling member 30 may comprise a heat pipe. In this case, cooling
member 30 may include a tube or other member containing a low
boiling temperature liquid, such as acetone or alcohol. In use,
heat from jaw members 22, 24 causes the liquid within a distal end
of the tube (toward portion 16) to vaporize, and this vapor may
subsequently condense at a proximal end of the tube (toward
handpiece 18) due to its relatively cooler temperature with respect
to the distal end. In this way, heat may transferred from the
distal end of instrument 14 to the proximal end and away from the
treated tissue.
[0032] Cooling members 30 may be constructed of aluminum, stainless
steel, or any other suitable electrically conductive or
non-conductive material. With reference to FIG. 6, if constructed
from an electrically conductive material, cooling members 30
themselves could actually function as electrodes without the need
for jaw members 22, 24. Cooling members 30 may then be arranged to
receive surgical energy from generator 12 for treating tissue, and
may contain a coolant therein which may be activated before,
during, and/or after the application of surgical energy. Again, the
size, shape, and overall configuration of cooling members 30 is not
limited to that depicted herein.
[0033] In the case of an electrosurgical device, application of
cooling member 30 may result in the `pigeon-holing` of the
electrical energy, focusing it on the tissue of interest.
Meanwhile, the increased thermal resistance allows cooling member
30 to more effectively conduct the thermal energy from the tissue
while the coolant may convect it away from the surgical area,
thereby decreasing the temperature of the tissue. Instrument 14
according to the present invention may not only perform the
surgical procedure more effectively, but due to the concentration
of electrical energy, may perform it more efficiently as well. In
the case of an ultrasonic device, where friction represents the
main component of thermal energy production, cooling member 30 may
again increase the local thermal resistance of the tissue, allowing
cooling member 30 to more effectively conduct the thermal energy
from the tissue while the coolant may convect it away from the
surgical area.
[0034] With reference again to FIGS. 1 and 2, handpiece 18 may
include a first actuator 40 for closing and opening jaw members 22,
24 to engage or release tissue therebetween. Proximal portions of
jaw members 22, 24 are disposed within a sheath 42 which is
operably connected to actuator 40 to allow for mechanical actuation
of jaw members 22, 24 via proximal and distal movement of sheath 42
as is known in the art. Of course, any other mechanism for opening
and closing jaw members 22, 24 is also fully contemplated. First
actuator 40 may also control the opening and closing of cooling
members 30 via movement of sheath 44 using a similar mechanism,
wherein the opening and closing of cooling members 30 and jaw
members 22, 24 may be synchronized. Alternatively, handpiece 18 may
include a second actuator 46 for mechanical actuation of cooling
members 30. With second actuator 46, cooling members 30 may be
actuated to engage and compress tissue before, after, or
simultaneous with jaw members 22, 24, and may be actuated to
release tissue before, after or simultaneous with jaw members 22,
24.
[0035] First actuator 40 and/or second actuator 46 may include a
return spring or other means for providing a biasing force to the
open position of jaw members 22, 24 and/or cooling members 30.
First actuator 40 and/or second actuator 46 could also include a
releasable locking mechanism such that constant depression of
either actuator 40 or 46 would not be required to maintain the
closed position of jaw members 22, 24 and/or cooling members 30.
Furthermore, the operation of first actuator 40 and second actuator
46 could be dependent upon one another such that, for example,
depression of second actuator 46 to move cooling members 30 to the
closed position would need to occur before first actuator 40 could
be depressed.
[0036] Whether controlled by first actuator 40 or second actuator
46, cooling members 30 may be arranged to apply a greater
compressive pressure on the tissue in their closed position
compared with the pressure applied by the clamping of jaw members
22, 24 in their closed position. In this way, an increased pressure
gradient may be induced on the tissue. Such a gradient may
effectively increase both the thermal and electrical resistance of
the tissue. Pressure applied by cooling members 30 alone, without
use of a coolant therein, is fully contemplated according to the
present invention. Therefore, application of cooling member 30 may
provide at least one of a pressure gradient or a thermal gradient
between cooling member 30 and jaw members 22, 24 to control thermal
spread during energy based surgical procedures, such as
electrosurgery or ultrasonic surgery.
[0037] As shown in FIG. 7, temperature sensors 50, such as
thermistors, may be provided on cooling members 30, jaw members 22,
24, or another area of tissue engaging portion 16 to provide
real-time, internal in vivo tissue temperature measurement during
surgical procedures.
[0038] In order to demonstrate the effectiveness of a cooling
member 30 according to the present invention, several experiments
were performed. With reference to FIG. 8, commercially available
ex-vivo chicken tissue and bipolar electrosurgery was used to test
the effects of a cooling channel placed alongside a surgical
instrument during coagulative surgical procedures. An Instech P625
Peristaltic Pump with 0.093'' ID tubing was used to flow chilled
water through the cooling channel at a flow rate of 3.3 mL/min.
Both SS 304 and Al 3003 were used as cooling channels.
[0039] The bite size for the surgical procedures was limited to 3/4
of the jaw length to avoid variations in tissue effect at the jaw
hinge area. Lateral tension to the tissue was avoided to ensure
effects were limited to the devices. The tissue temperature was
measured on both sides of the electrosurgical tool at a depth of
2.0 mm under the tissue surface using thermistors placed at 2.5,
3.0, and 3.5 mm from the tool edge. Polycarbonate fixtures were
created for the device tested to ensure temperature measurements
were recorded at precise distances from the tool edge (see FIG. 8).
Upon tissue clamping, the fixture was placed around the device and
held lightly in place while the trials proceeded.
[0040] The following scenarios were tested: (1) no cooling channel
in place (control), (2) SS cooling channel in place with no
coolant, (3) Al cooling channel in place with coolant, and (4) SS
cooling channel in place with coolant. In the control group, the
average ratio of temperatures from the left side of the tool to the
right side tool (FIG. 8) at 2.5 mm, 3.0 mm, and 3.5 mm away from
the tool edge was 1.14, 0.99, and 1.05 with a standard deviation of
0.12, 0.12, and 0.12 respectively, where an exemplary illustration
of the results of this trial is shown in FIG. 10.
[0041] With reference to FIGS. 9 and 11, for group (2) the average
ratio of temperatures from the left side (no cooling channel) to
the right side (cooling channel without coolant) at 2.5 mm, 3.0 mm,
and 3.5 mm away from the tool edge was 2.08, 1.31, and 1.54 with a
standard deviation of 0.54, 0.52, and 0.51 respectively. With
reference to FIGS. 9 and 12, for group (3) the average ratio of
temperatures from the left side (no cooling channel) to the right
side (cooling channel with coolant) at 2.5 mm, 3.0 mm, and 3.5 mm
away from the tool edge was 3.13, 3.47, and 2.82 with a standard
deviation of 1.22, 2.56, and 1.26 respectively. For group (4), the
average ratio of temperatures from the left side (no cooling
channel) to the right side (cooling channel with coolant) at 2.5
mm, 3.0 mm, and 3.5 mm away from the tool edge was 3.12, 2.64, and
2.84 with a standard deviation of 1.26, 0.89, and 0.79
respectively.
[0042] Therefore, data collected indicates a much lower temperature
realized for tissue being actively cooled compared to tissue left
thermally untreated. Use of the cooling member showed adequate
tissue temperature reduction in tissue as close as 2.5 mm from the
tool edge to avoid permanent thermal damage at those distances. As
shown in FIG. 11, the high thermal gradients created near the right
side of the surgical device resulted in much less thermal spread
for the case of a SS304 cooling tube without coolant being
positioned next to the device, and was almost completely eliminated
when coolant flowing at 3.3 mL/min was passed through either an
Al3003 or SS304 cooling channel as demonstrated in FIG. 12.
[0043] The results obtained from actively cooling local tissue
during electrosurgical procedures demonstrate the ability to
minimize and possibly eliminate the thermal spread associated with
surgical tools that rely on the production of heat to coagulate
and/or cut tissue. The reduction in thermal spread seen simply with
the application of the cooling member suggests that even the modest
pressure placed on the tissue by the tube increases both the
thermal and electrical resistance of the tissue. The significantly
increased thermal conductivity of the tube over the tissue
(.about.0.5 W/mK) may allow the cooling member to conduct most of
the heat that would normally be retained by the tissue resulting in
increasing tissue temperature. The addition of coolant flowing
through the tube allows the convective qualities of the coolant to
convect the heat conducted by the cooling member and transmit it
away from the surgical site. By maintaining the cooling member at
as low a temperature as possible, a high thermal gradient may be
created allowing for maximum heat conduction by the cooling
member.
[0044] In further accordance with the present invention, FIG. 13
depicts a control system 60 for controlling the temperature
distribution within the treated tissue. Control system 60 may use
temperature sensors such as thermistors 62 placed locally in
sensitive tissue to monitor the tissue temperature 63 in real-time
during surgery. Algorithms may be used to convert 64 the
temperature to a thermal dose so as to continuously monitor the
thermal dose 66 the tissue has absorbed. This data may serve as an
input in control system 60 where both the power 68 output by
surgical generator 12 as well as the flow rate 70 of coolant within
cooling member 30 may be controlled by that input. In addition, a
tissue model 72 may be utilized for predicting and controlling
tissue heating, which may be helpful in areas hard to reach by
temperature sensors, such as in brain or spinal electrosurgery.
Inputs of tissue model 72 may include tissue type, electrode type,
presence of cooling member 30, tissue resistance (determined, for
example, via a pressure sensor or tissue thickness), and others,
where model 72 may be used to predict the temperature gradient,
resulting thermal dose, and surgical time for the treated tissue
area.
[0045] For example, cooling member 30 could be modeled as a
circular pipe with constant wall heat flux. Assuming fully
developed flow has been established the non-dimensionalized
governing equation becomes:
T(x,r)=T.sub.as(r)+T.sub.en(x,r)
where
T.sub.as=C.sub.0+C.sub.1x+.theta.(r), [0046] .theta.(r)=centerline
temperature and [0047] T.sub.en is a Sturm-Louiville problem in r
with BC of constant heat flux.
[0048] Using the power output from generator 12 as another input
along with the material properties of the tissue, cooling member
30, and coolant, the temperature of the tissue at discrete
distances from tissue engaging portion 16 may be determined. Also,
in surgical practice, the temperature gradient of the coolant could
be used as a control input if the distance from instrument 16 is
known. If this is so, tissue temperature could be monitored
indirectly through the coolant.
[0049] While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and
describe all possible forms of the invention. Rather, the words
used in the specification are words of description rather than
limitation, and it is understood that various changes may be made
without departing from the spirit and scope of the invention.
* * * * *