Note: Descriptions are shown in the official language in which they were submitted.
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ABHERENT SURG~ CAL INSTRUMENT AND ME~HOD
Background of the Invention
Surgical devices which heat the tissue to provide
hemostasis are described in the literature (seP, for example,
U. S. Patents RE 29,088, 4,091,813 and 4,18~,632). The ad-
herence of tissue to such surgical devices severely limits their
usefulness because the resulting avulsion of tissue causes un-
desirable tissue damage and bleeding. Also, the adherence of
tissue to such surgical devices limits the surgeon's control of
the device, and the build-up of adherent tissue material causes
apparent dullness of the device. Additionallyl the build-up of
adherent tissue materlal on heater-type surgical devices intro-
duces a high thermal impedance between the heater and the tissue
being cut that prevents heating of the tissues to the desired
temperature. These problems of tissue adhering to the surgical
device are especially severe for tissue temperatures within the
range from about 100C. to about 500C.
Summary of the Invention
Applicant has discovered that the tissue temperature for
the optimum condition of hemostasis with minimal tissue damage
varies with the type of tissue being cut and may be as low as
about 130C. (on the soft palate of the mouth) and as high as
about 450C. to 500C. (on highly vascularized tissue), above
which tissue adherence usually does not occur. In accordance
with the present invention, the optimum conditions of hemostasis
with minimal tissue damage can be attained by operating at tissue
temperatures in the range from about 100C. to about 500C. and
by introducing between the surgical device and the contacted
tissue an abherent coating having specific thermal parameters.
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More particularly, in surgical apparatus which operates
at elevated temperatures for heating the tissue contacted there-
by, the heat transfer from the apparatus to the tissue in regions
of the apparatus in contact with tissues may be twenty times
greater than the heat transfer from the apparatus to the air in
regions of the apparatus that are not in contact with tissue.
The heat transfer conditions vary widely as a function of the
type of tissue being cut, the desired operating temperature, and
the speed at which the device is moved through tissue.
To obtain optimum conditions of hemostasis with minimal
tissue damage, the surgical device should rapidly elevate the
temperature of the tissue to a preselected narrow range (usually
between 100C. and 500C.) and should maintain the tissue temper-
ature wlthin that range as cutting proceeds.
~ ny accumulation of tissue on that portion of the surgical
device that contacts tissue can interpose a thermal impedance
between the device and the tissues which may inhibit heat transfer
and cause the temperature o the contacted tissue to drop below
the value at which the optimum conditions of hemostasis with
minimal tissue damage occur. Therefore, according to the present
invention, an abherent coating is provided on the tissue-
contacting surface of the surgical device which has thermal
properties and characteristics within specific limits to assure
that the temperature of tissue remains within the optimum range
for which hemostasis and minimal tissue damage occur.
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Various asDects of the invention are as follows:
Surgical apparatus for rapidly cutting tissue
and simultaneously heating such tissue in abherent contact
therewith to an elevated temperature to provide hemostasis
with minimal tissue damage, the apparatus com~rising:
blade means having a tissue-cutting edge
for rapidly severing tissue as the blade means moves
therethrough;
heating means disposed on the blade means and
.10 operable to heat the tissue-cutting edge to an elevated
temperature for heating the tissue being cut thereby;
and
electrlcally-insulating abherent coatlng means
disposed intermediate the heating means and the tissue
being cut to electrically lnsulate the surgical apparatus
from the tissue being cut.
The method of preventing surgical apparatus
which has a tissue-cutting edge to permit rapid movement
through tissue from adhering to the tissue being cut
thereby while simultaneously heating such tissue to an
elevated temperature at which hemostasis with minimal
tissue damage occurs, the method comprising the steps
of:
heating the surgical apparatus during the rapid
movement thereof through tissue being cut thereby;
transferring heat to the tissue being cut from
the surgical apparatus; and
interposing between the tissue being cut and
the surgical apparatus an electrically-insulati~g abherent
coating for electrically isolating the surgical apparatus
from the tissue being cut.
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Figure 3 is a cross-sectional view of another embodiment
of the present invention in which a heated surgical hemostat
includes an abherent coating;
Figure 4 is a cross-sectional view of another embodiment
of the present invention in which a sintered porous blade struc-
ture with interconnecting passages provides a reservoir of
abherent material;
Figure 5 is a detailed cross-sectional view of an
embodiment of the present invention which illustrates the abherent
coating on the surgical instrument disposed adjacent to the tissue
being cut; and
Figure 6 is a graph which illustrates the parameters of
an abherent coating according to the present invention.
Detailed Description of the Preferred Embodiments
Referring now to Figure 1, there i6 shown a surgical
scalpel having a blade portion 11 with a cutting edge lO and an
attached handle portion 8 which also carries a conductor of
heating power from source 9 to the blade 11 to heat the same, as
taught in the prior art. As shown in Figure 2, the surfaces of
the blade ll, at least near the cutting edge 10, operate at
elevated temperatures and contact tissue 13 via an abherent
coating 12 interposed between the blade ll and tissue 13. This
eliminates the problem of tissue 13 sticking to the surfaces of
blade 11 ~ut introduces a thermal impedance between the heated
blade 11 and the tissue 13 in contact therewith.
It has been determined that for portions of the blade 11
in contact with tissue, the heat flux 14 normal to or through
the abherent coati.ng 12 is approximately 10 to 20 times greater
than the heat flux therethrough to the air for portions of the
blade 11 not in contact with tissue. This produces temperature
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differences across the abherent coating 12. Thus, while the
bla~e 11 is out of contact with tissue 13, the effective
surface temperature of abherent coating 12 is approximately
the same as the temperature of the blade 11. However, when
the blade 11 and abherent coating 12 contact the tissue 13,
the heat flux 14 passing through the thermal impedance presented
by abherent coating 12 causes the surface temperature of ab-
herent coating 12 to decrease below the desired temperature at
which the optimum condition of hemostasis and minimal tissue
damage occur. The temperature of the surface of abherent
coating 12 may be increased to the desired temperature by in-
creasing the temperature of the blade 11 by an amount sufficient
to overcome the thermal drop across the abherent coating 12.
However, because of the transient conditions associated with
the blade 11 bein~ in and out of contact with tissue 13 during a
surgical procedure, the surface temperature of the abherent
coating 12 may rise excessively while out of contact with tissue
to cause deterioration of the abherent coating 12 and undesirable
tissue damage upon recontact with tissue 13, as well as falling
excessively when coming into contact with tissues to temperatures
that are not hemostatic.
In contrast to these transient operating conditions in
surgery, conventional cookware with abherent coatings do not in-
volve transient operation. The heat transfer rate to an item
being cooked is generally constant and is established without
regard for damage to living tissue. Cookware also can be
operated at higher temperatures to overcome the effects of high
thermal impedance associated with thicker abherent coatings.
However, for reasons stated above, surgical devices cannot be
arbitrarily set at a temperature significantly higher than the
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optimum temperature at which hemostasis with minimal tissue
damage occurs. Also, the thicknesses of coatin9s typically
used on cookware cannot be used on surgical devices because of
the blunting effect and degradation of the cutting action of a
blade that would result.
In accordance with the present invention, the abherent
coating 12 may be formed as a solid layer or as a sacrificial
solid layer or as a sacrificial liquid layer. A solid abherent
layer 12 may be formed on the device 11 including materials such
as fluorocarbon polymers (exemplified by the fluorinated ethylene-
propylene copolymers, polytetrafluoroethylene and polyethylene
terephthalatet, or silicones and polydimethylsiloxanes with
act~ve end groups, for example, of hydroxyl, amine, epoxide or
thiol attached to the silicone polymer via a nonhydrolyzable
Si-C bond, or fluoride-metal composites such as fluoride impreg-
nated composites, or organic phosphates. Alternatively, a
sacrificial solid abherent coating may be formed using materials
such as silicone greases or hydrocarbon, synthetic and natural
ester waxes, or sulfide compounds. In addition, a sacrificial
solid abherent coating may be formed using fluorinated ethylene-
propylene copolymers which have been found to be effective in
that a coating thus formed "sloughs off n in thin platelets with
use to provide the desired abherent characteristics with respect
to tissue~
With respect to Figure 4, a sacrificial liquid abherent
coating may be provided by forming a sintered or porous blade
structure 11 with substantially continuous passages therethrough
which can be impregnated with a material such as ~ilicone oil,
for example, of the type based on dimethyl silicone, or ethers
such as perfluoropoly-synthetic fluids. The porous and
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impregnated structure according to Figure 4 thus establishes
and maintains a continuous film of abherent material 12 at the
surface of the device 11 which is disposed to contact tissue 13.
In accordance with the present invention, the thermal
impedance of the abherent coating must be sufficientl~ low to
permit transfer of heat 14 from the device 11 to the tissue 13
in contact therewith as illustrated in Figure 5. In particular,
the tolerable thermal impedance of an abherent coating 12 depends
generally upon the level of heat flux required for a particular
surgical application. For example, in ophthalmic, neurological
and plastic, and dermatological surgery procedures, hemostasis
can be accomplished while cutting using heat fluxes well below
50 watts/cm . However, surgical procedures involving incisions
in highly vascular tissues or rapid movement through tissue may
require heat fluxes above S0 watts/cm to achieve hemostasis
while cutting.
As used herein, "thermal impedance" is defined as follows:
R = hT
(Q/A)
where R refers to the thermal impedance of the abherent coating
0 in units of C- cm , QT refers to the temperature difference
watt
across the abherent coating from the interface of the device 11/
abherent coating 12 to the outer surface of the abherent coating
12, in units of C., and Q/A refers to the heat flux flowing
normal to or through the abherent coating, in units of watts/cm2.
Referring to Figure 5, the maximum allowed temperature
difference ~T across the abherent coating under maximum heat
flux conditions should not substantially exceed about 50C. in
order to optimize hemostasis while minimizing tissue damage and
29 avoiding exposure of the surgical device and the abherent coating
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to damaging temperatures. This tolerable temperature difference
thus establishes the thermal impedance for the heat flux levels
that will be encountered during use of the surgical device. The
thermal impedances, as defined above, for abherent coatings 12
operating at specified levels of heat flux are summariæed below:
Heat Flux, Q/AMaximum Allowed Thermal Impedance, R,
(watts/cm2)for Temperature Difference, ~T, of 50C.
_
5.0
2.5
1.7
1~3
1.0
100 0,5
These values of thermal impedance for the abherent coating
can establish the rnaximum allowed thickness for various abherent
coatings. Referring to Figure 5, the allowed thickness of ab-
herent coating 12 in a direction normal to the heat flux 14 is
given by the relationship:
t = R-k
where t refers to the maximum allowed abherent coating thickness
in units of centimeters, R is the thermal impedance, as defined
previously, and k refers to effective thermal conductivity of
abherent coating 12 in units of watts/cmC.
The graph of Figure 6 illustrates the relationship
between maximum thickness 18 of the abherent coating 12 and heat
flux levels corresponding to high (100 watts/cm maximum) and low
~30 watts/cm maximum) heat flux requirements associated with
various surgical procedures. By way of examp~e, certain fluoro-
carbon materials that have been found efective as abherent
coatings exhibit a thermal conductivity of about .0025 watts/cmC.
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1 161326
In accordance with the above, the thickness of an abherent
coating of this material should not be greater than .0013 cm
(0.5 mil) for operation at high heat flux levels.
In the apparatus of Figure 3, a pinch-type instrument 15
(such as a hemostat) may be heated in conventional manner by a
source of heating power connected thereto to transfer heat 14 to
tissue 16 via the abherent coating 12 interposed therebetween.
The maximum allowed thickness of abherent coating 12 is
determined, as discussed above, with respect to the thermal
impedance of the coating material and the operating level of
heat flux involved.
