Note: Descriptions are shown in the official language in which they were submitted.
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ELECTROSURGICAL INSTRUMENT REDUCING THERMAL SPREAD
BACKGROUND
The present disclosure relates to electrosurgical instruments used
for open and endoscopic surgical procedures. More particularly, the present
disclosure relates to a bipolar forceps having an electrode assembly which is
designed to limit and/or reduce thermal spread to adjacent tissue structures
and
reduce the incidence of flashover during activation.
Technical Field
A hemostat or forceps is a simple plier-like tool which, uses
mechanical action between its jaws to constrict tissue and is commonly used in
open surgical procedures to grasp, dissect and/or clamp tissue.
Electrosurgical
forceps utilize both mechanical clamping action and electrical energy to
effect
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hemostasis by heating the tissue and blood vessels to coagulate, cauterize
and/or
seal tissue.
By utilizing an electrosurgical forceps, a surgeon can either
cauterize, coagulate/desiccate tissue and/or simply reduce or slow bleeding by
controlling the intensity, frequency and duration of the electrosurgical
energy
applied to the tissue. Generally, the electrical configuration of
electrosurgical
forceps can be categorized in two classifications: 1) monopolar
electrosurgical
forceps; and 2) bipolar electrosurgical forceps.
Monopolar forceps utilize one active electrode associated with the
clamping end effector and a remote patient return electrode or pad which is
attached externally to the patient. When the electrosurgical energy is
applied, the
energy travels from the active electrode, to the surgical site, through the
patient
and to the return electrode.
Bipolar electrosurgical forceps utilize two generally opposing
electrodes which are generally disposed on the inner facing or opposing
surfaces
of the end effectors which are, in turn, electrically coupled to an
electrosurgical
generator. Each electrode is charged to a different electric potential. Since
tissue
is a conductor of electrical energy, when the end effectors are utilized to
clamp,
grasp, seal and/or cut tissue therebetween, the electrical energy can be
selectively transferred through the tissue.
Over the last several decades, more and more surgeons are
complimenting traditional open methods of gaining access to vital organs and
body cavities with endoscopes and endoscopic instruments which access organs
through small puncture-like incisions. Endoscopic instruments are inserted
into
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the patient through a cannula, or port, that has been made with a trocar.
Typical
sizes for cannulas range from three millimeters to twelve millimeters. Smaller
cannulas are usually preferred, which, as can be appreciated, ultimately
presents
a design challenge to instrument manufacturers who must find ways to make
surgical instruments that fit through the cannulas.
Certain surgical procedures require sealing blood vessels or
vascular tissue. However, due to space limitations surgeons can have
difficulty
suturing vessels or performing other traditional methods of controlling
bleeding,
e.g., clamping and/or tying-off transected blood vessels. Blood vessels, in
the
range below two millimeters in diameter, can often be closed using standard
electrosurgical techniques. If a larger vessel is severed, it may be necessary
for
the surgeon to convert the endoscopic procedure into an open-surgical
procedure
and thereby abandon the benefits of laparoscopy.
It is known that the process of coagulating small vessels is
fundamentally different than vessel sealing. For the purposes herein the term
"coagulation" is defined as a process of desiccating tissue wherein the tissue
cells
are ruptured and dried. The term "vessel sealing" is defined as the process of
liquefying the collagen in the tissue so that the tissue cross-links and
reforms into
a fused mass. Thus, coagulation of small vessels is sufficient to close them,
however, larger vessels need to be sealed to assure permanent closure.
Several journal articles have disclosed methods for sealing small
blood vessels using electrosurgery. An article entitled Studies on Coagulation
and
the Development of an Automatic Computerized Bipolar Coagulator, J.
Neurosurg., Volume 75, July 1991, describes a bipolar coagulator which is used
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to seal small blood vessels. The article states that it is not possible to
safely
coagulate arteries with a diameter larger than 2 to 2.5 mm. A second article
is
entitled Automatically Controlled Bipolar Electrocoagulation - "COA-COMP",
Neurosurg. Rev. (1984), pp. 187-190, describes a method for terminating
electrosurgical power to the vessel so that charring of the vessel walls can
be
avoided.
With particular respect to vessel sealing, in order to effect a proper
seal with larger vessels, two predominant mechanical parameters must be
accurately controlled - the pressure applied to the vessel and the gap between
the electrodes both of which affect thickness of the sealed vessel. More
particularly, accurate application of the pressure is important for several
reasons:
1) to oppose the walls of the vessel; 2) to reduce the tissue impedance to a
low
enough value that allows enough electrosurgical energy through the tissue; 3)
to
overcome the forces of expansion during tissue heating; and 4) to contribute
to
the end tissue thickness which is an indication of a good seal. In some
instances
a fused vessel wall is optimum between 0.001 and 0.006 inches. Below this
range, the seal may shred or tear and above this range the lumens may not be
properly or effectively sealed.
Numerous bipolar electrosurgical instruments have been proposed
in the past for various open and endoscopic surgical procedures. For example,
U.S. Patent No. 2,176,479 to Willis, U.S. Patent Nos. 4,005,714 and 4,031,898
to
Hiltebrandt, U.S. Patent Nos. 5,827,274, 5,290,287 and 5,312,433 to Boebel et
al., U.S. Patent Nos. 4,370,980, 4,552,143, 5,026,370 and 5,116,332 to
Lottick,
U.S. Patent No. 5,443,463 to Stern et al., U.S. Patent No. 5,484,436 to Eggers
et al. and U.S. Patent No. 5,951,549 to Richardson et al., all relate to
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electrosurgical instruments for coagulating, sealing and/or cutting vessels or
tissue.
It has been found that using electrosurgical instruments to seal, cut
and/or cauterize tissue may result in some degree of so-called "thermal
spread"
across adjacent tissue structure. For the purposes herein the term " thermal
spread" refers generally to the heat transfer (heat conduction, heat
convection or
electrical current dissipation) traveling along the periphery of the
electrically
conductive surfaces. This can also be termed "collateral damage" to adjacent
tissue. As can be appreciated, reducing the thermal spread during an
electrical
procedure reduces the likelihood of unintentional or undesirable collateral
damage to surrounding tissue structures which are adjacent to an intended
treatment site.
Instruments which include dielectric coatings disposed along the
outer surfaces are known and are used to prevent tissue "blanching" at points
normal to the activation site. In other words, these coatings are primarily
designed to reduce accidental burning of tissue as a result of incidental
contact
with the outer surfaces end effectors. So far as is known these coating are
not
designed or intended to reduce collateral tissue damage or thermal spread to
adjacent tissue (tissue lying along the tissue plane).
It has also been found that cleaning and sterilizing many of the prior
art bipolar instruments is often impractical as electrodes and/or insulation
can be
damaged. More particularly, it is known that electrically insulative
materials, such
as plastics, can be damaged or compromised by repeated sterilization cycles
which may ultimately effect the reliability of the instrument and cause so-
called
"flashover." Flashover as used herein relates to a visual anomaly which
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develops as a result of inconsistent current tracking over the surface of the
insulator or insulative coating and/or activation irregularities which may
occur
when the instrument is repeatedly used during surgery. Put simply, flashover
tends to char the surface of the insulate and may effect the life of the
instrument and/or the electrode assembly. The effects and industry standards
with respect to flashover are discussed in detail in the Annular Book of ASTM
Standards, Vol. 10.02, Designations: D495-84; D618; D2303; and D3638.
Several electrosurgical instruments have been introduced which
are known to solve many of the aforementioned problems associated with
sealing, cutting, cauterizing and/or coagulating differently-sized vessels.
Some
of these instruments are described in U.S. Patent No. 6,277,117, U.S. Patent
No. 6,511,480, and U.S. Patent No. 6,585,735.
Thus, a need exists to develop an electrosurgical instrument
which includes can effectively reduce the undesirable effects of thermal
spread
across tissue structures and effectively reduce the incidence of flashover.
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SUMMARY
The present disclosure generally relates to an open and/or
endoscopic electrosurgical instrument which includes electrodes which are
electrically and thermally isolated from the remainder of the instrument by a
uniquely designed insulating substrate and electrically conductive surface. It
is
envisioned that the geometric shape of the insulating substrate relative to
the
geometric shape of the conductive surface contributes to the overall reduction
of
collateral damage to adjacent tissue structures. The uniquely-designed
geometric
configuration of the insulating substrate in connection with the chemical
characteristics of the insulating substrate also contributes to a reduction in
the
incidence of flashover.
More particularly, the present disclosure relates to an electrosurgical
instrument which includes opposing end effectors and a handle for effecting
movement of the end effectors relative to one another. The instrument includes
a
housing and a pair of electrodes. Each electrode preferably includes an
electrically conductive surface (e.g., which can be dimensioned for sealing,
clamping and/or cutting) and an insulating substrate which is dimensioned to
be
selectively engageable with the end effectors such that the electrodes reside
in
opposing relation relative to one another. The dimensions of the insulating
substrate are different from the dimensions of the electrically conductive
surface
to reduce thermal spread to adjacent tissue structures. The insulating
substrate
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is made from a material having a Comparative Tracking Index of about 300 volts
to about 600 volts to reduce the incidence of flashover
Preferably, the dimensions of the insulating substrate are different
from the dimensions of the electrically conductive surface which not only
reduces
thermal spread to adjacent tissue structures but may contribute to a reduction
in
the incidence of flashover.
In other embodiments, the insulating substrate is mounted to the
electrically conductive surface by stamping, by overmolding, by overmolding a
stamped plate and/or by overmolding a metal injection molded plate. All of
these
manufacturing techniques produce an electrode having an electrically
conductive
surface which is substantially surrounded by an insulating substrate. These
uniquely described embodiments described herein are contemplated to
effectively
reduce the thermal spread to adjacent tissue structures during and/or
immediately
following activation. Moreover, certain cross section deviations may also
contribute to a reduction in the incidence of flashover. The electrically
conductive
surface may also include a pinch trim which facilitates secure engagement of
the
electrically conductive surface to the insulating substrate and also
simplifies the
overall manufacturing process.
In another embodiment, the electrically conductive surface includes
an outer peripheral edge which has a radius and the insulator meets the
electrically conductive surface along an adjoining edge which is generally
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tangential to the radius and/or meets along the radius. Preferably, at the
interface, the electrically conductive surface is raised relative to the
insulator.
The insulating substrate may be made from a plastic or plastic-
based material having a Comparative Tracking Index of about 300 volts to about
600 volts. Preferably, the insulating substrate is substrate is made from a
group
of materials which include Nylons, Syndiotactic-polystryrene (SPS),
Polybutylene
Terephthalate (PBT), Polycarbonate (PC), Acrylonitrile Butadiene Styrene
(ABS),
Polyphthalamide (PPA), Polymide, Polyethylene Terephthalate (PET), Polyamide-
imide (PAI), Acrylic (PMMA), Polystyrene (PS and HIPS), Polyether Sulfone
(PES), Aliphatic Polyketone, Acetal (POM) Copolymer, Polyurethane (PU and
TPU), Nylon with Polyphenylene-oxide dispersion and Acrylonitrile Styrene
Acrylate. Alternatively, a non-plastic insulating material, e.g., ceramic, may
be
used in lieu of or in combination with one or more of the above-identified
materials
to facilitate the manufacturing process and possibly contribute to the overall
reduction of thermal spread to adjacent tissue structures
In another embodiment of the present disclosure, the insulating
substrate of each electrode includes at least one mechanical interface for
engaging a complimentary mechanical interface disposed on the corresponding
end effector of the instrument. Preferably, the mechanical interface of the
substrate includes a detent and the mechanical interface of the corresponding
end effector includes a complimentary socket for receiving the detent.
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Other embodiments of the present disclosure include a housing
having a bifurcated distal end which forms two resilient and flexible prongs
which
each carry an electrode designed to engage a corresponding end effector. In
another embodiment, the end effectors are disposed at an angle (a) relative to
the
distal end of the shaft of the electrosurgical instrument. Preferably, the
angle is
about sixty degrees to about seventy degrees. The end effectors and, in turn,
the
electrodes, can also be dimensioned to include a taper along a width "W" (See
Fig. 2).
The present disclosure also relates to an electrosurgical instrument
having a handle and at least one shaft for effecting movement of a pair of
opposing end effectors relative to one another. An electrode assembly engages
the shaft and includes a pair of electrodes. Each electrode is removably
engageable with a corresponding end effector and includes an electrically
conductive surface with a first geometric shape and an insulating substrate
with a
second geometric shape. Preferably, the second geometric shape of the
insulating substrate is different from the first geometric shape of the
conductive
surface which effectively reduces thermal spread to adjacent tissue structures
and may also contribute to a reduction in the incidence of flashover.
In one embodiment, the electrode assembly which engages the
instrument is removable, disposable and replaceable after the electrode
assembly
is used beyond its intended number of activation cycles. Alternatively, the
electrode assembly and/or the electrodes may be integrally associated with the
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end effectors of the instrument and are not removable. In this instance, the
electrosurgical instrument (open or endoscopic) may be designed for single use
applications and the entire instrument is fully disposable after the surgery
is
completed.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of an open electrosurgical instrument
according to one embodiment of the present disclosure;
Fig. 2 is an enlarged, perspective view of a distal end of the
electrosurgical instrument shown in Fig. 1;
Fig. 3 is a perspective view with parts separated of the
electrosurgical instrument shown in Fig. 1;
Fig. 4 is an enlarged, side view of an electrode assembly of Fig. 1
shown without a cover plate;
Fig. 5 is an enlarged, perspective view of a distal end of the
electrode assembly of Fig. 4;
Fig. 6 is a perspective view with parts separated of an upper
electrode of the electrode assembly of Fig. 5;
Fig. 7A is a perspective view with parts separated of a lower
electrode of the electrode assembly of Fig. 5;
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Fig. 7B is a cross section of a prior art electrode configuration with
the electrode extending over the sides of the insulator;
Fig. 7C is a cross section of an electrode with the insulator
extending beyond the sides of a radiused electrode;
Fig. 7D is a cross section of an overmolded stamped electrode
configuration showing the insulator capturing a pinch trim which depends from
the
electrically conductive surface;
Fig. 7E is a cross section of an electrode configuration showing a
compliant barrier disposed about the periphery of the opposing electrodes and
insulators which controls/regulates the heat dissipating from the conductive
surface.
Fig. 8A is a perspective view of the open forceps of the present
disclosure showing the operative motion of the electrosurgical instrument
about a
tubular vessel;
Fig. 8B is a perspective view of an endoscopic version of the
present disclosure showing the operative motion of the instrument;
Fig. 9 is an enlarged, partial perspective view of a sealing site of a
tubular vessel;
Fig. 10 is a longitudinal cross-section of the sealing site taken along
line 10-10 of Fig. 9;
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Fig. 11 is a longitudinal cross-section of the sealing site of Fig. 9
after separation of the tubular vessel;
Fig. 12 is a contour plot showing the dissipation of the
electrosurgical current across the tissue using an electrode without
insulation;
Fig. 13A is a contour plot showing the dissipation of the
electrosurgical current across the tissue using an electrode with flush
insulator;
Fig. 13B is an enlarged contour plot of FIG. 13A showing the current
concentration and relative dissipation of the electrosurgical current at an
adjoining
edge or interface between the insulator and the electrically conductive
surface;
Fig. 13C is an enlarged electrical field magnitude plot of the
electrode configuration of Fig. 13A showing the current concentration and
relative
dissipation of the electrosurgical field distribution at an adjoining edge or
interface
between the insulator and the electrically conductive surface;
Fig. 14A is a contour plot showing the dissipation of the
electrosurgical current across the tissue using an electrode with a raised
electrically conductive surface and a radiused interface between the
electrically
conductive surface and the insulator;
Fig. 14B is an enlarged contour plot of FIG. 14A showing the current
concentration and relative dissipation of the electrosurgical current at an
adjoining
edge or interface between the insulator and the electrically conductive
surface;
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Fig. 14C is an enlarged electrical field magnitude plot of the
electrode configuration of Fig. 14A showing the current concentration and
relative
dissipation of the electrosurgical field distribution at an adjoining edge or
interface
between the insulator and the electrically conductive surface; and
Fig. 15 is a contour plot showing the dissipation of the
electrosurgical current across the tissue using an electrode with a raised
electrically conductive surface and a ninety degree (90 ) interface between
the
electrically conductive surface and the insulator.
DETAILED DESCRIPTION
It has been found that by altering the configuration of the electrode
insulating material relative to the electrically conductive surface, surgeons
can
more readily, more easily and more effectively reduce thermal spread across or
to
adjacent tissue and/or reduce the incidence of flashover. For the purposes
herein
the term " thermal spread" refers generally to the heat transfer (heat
conduction,
heat convection or electrical current dissipation) dissipating along the
periphery of
the electrically conductive or electrically active surfaces to adjacent
tissue. This
can also be termed "collateral damage" to adjacent tissue. The term
"flashover" is
simply a visual anomaly which occurs during activation as a result of
inconsistent
and/or irregular current tracking over the surface of the insulate which may
occur
when the instrument is repeatably used during surgery. Flashover tends to char
the surface of the insulate and may effect the life of the instrument.
It is envisioned that the configuration of the insulating material which
surrounds the perimeter of the electrically conductive surface will
effectively
reduce current and thermal dissipation to adjacent tissue areas and generally
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restrict current travel to areas between the opposing electrodes. As mentioned
above, this is different from dielectrically coating the outer surfaces of the
instrument to prevent tissue "blanching" at points normal to the intended
site.
These coatings are not designed or intended to reduce collateral tissue damage
or thermal spread to adjacent tissue (tissue lying along the tissue activation
plane).
More particularly, it is contemplated that altering the geometrical
dimensions of the insulator relative to the electrically conductive surface
alters the
electrical path thereby influencing the thermal spread/collateral damage to
adjacent tissue structures. Preferably, the geometry of the insulating
substrate
also isolates the two electrically opposing poles (i.e., electrodes) from one
another thereby reducing the possibility that tissue or tissue fluids can
create an
unintended bridge or path for current travel. In other words, the insulator
and
electrically conductive surface are preferably dimensioned such that the
current is
concentrated between the opposing electrically conductive surfaces as
explained
in more detail below.
It is also contemplated that one way to reduce the incidence of
flashover is to alter the geometry of the insulation relative to the
electrically
conductive surface which effectively increases the overall distance that the
electrical current must travel along the predetermined electrical path. It is
also
envisioned that manufacturing the insulating substrate from a specific
material
having certain properties will, likewise, reduce the incidence of flashover
during
activation.
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Referring now to Figs. 1-3, a bipolar forceps 10 for use with open
surgical procedures is shown by way of example and includes a mechanical
forceps 20 and an electrode assembly 21. In the drawings and in the
description
which follows, the term "proximal", as is traditional, will refer to the end
of the
forceps 10 which is closer to the user, while the term "distal" will refer to
the end
which is further from the user. In addition, although the majority of the
figures,
i.e., Figs 1-7A and 8A, show one embodiment of the presently described
instrument for use with open surgical procedures, e.g., forceps 20, it is
envisioned
that the same properties as shown and described herein may also be employed
with or incorporated on an endoscopic instrument 100 such as the embodiment
shown by way of example in Fig. 8B.
Figs. 1-3 show mechanical forceps 20 which includes first and
second members 9 and 11 which each have an elongated shaft 12 and 14,
respectively. Shafts 12 and 14 each include a proximal end 13 and 15 and a
distal end 17 and 19, respectively. Each proximal end 13, 15 of each shaft
portion 12, 14 includes a handle member 16 and 18 attached thereto which
allows
a user to effect movement of at least one of the shaft portions, e.g., 12
relative to
the other, e.g. 14. Extending from the distal ends 17 and 19 of each shaft
portion
12 and 14 are end effectors 24 and 22, respectively. The end effectors 22 and
24
are movable relative to one another in response to movement of handle members
16 and 18.
Preferably, shaft portions 12 and 14 are affixed to one another at a
point proximate the end effectors 24 and 22 about a pivot 25 such that
movement
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of one of the handles 16, 18 will impart relative movement of the end
effectors 24
and 22 from an open position wherein the end effectors 22 and 24 are disposed
in spaced relation relative to one another to a closed position wherein the
end
effectors 22 and 24 incorporate a tubular vessel 150 therebetween (see Figs.
8A
and 8B) to effect sealing, cutting or grasping. It is envisioned that pivot 25
has a
large surface area to resist twisting and movement of forceps 10 during
activation.
It is also envisioned that the forceps 10 can be designed such that movement
of
one or both of the handles 16 and 18 will only cause one of the end effectors,
e.g., 24, to move with respect to the other end effector, e.g., 22.
As best seen in Fig. 3, end effector 24 includes an upper or first jaw
member 44 which has an inner facing surface 45 and a plurality of mechanical
interfaces disposed thereon which are dimensioned to releasable engage a
portion of the electrode assembly 21 which will be described in greater detail
below. Preferably, the mechanical interfaces include sockets 41 which are
disposed at least partially through inner facing surface 45 of jaw member 44
and
which are dimensioned to receive a complimentary detent 122 attached to upper
electrode 120 of the disposable electrode assembly 21. While the term "socket"
is used herein, it is contemplated that either a male or female mechanical
interface may be used on jaw member 44 with a mating mechanical interface
disposed on the electrode assembly 21.
In some cases, it may be preferable to manufacture mechanical
interfaces 41 along another side of jaw member 44 to engage a complimentary
mechanical interface of the electrode assembly 21 in a different manner, e.g.,
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from the side. Jaw member 44 also includes an aperture 67 disposed at least
partially through inner face 45 of end effector 24 which is dimensioned to
receive
a complimentary guide pin 124 disposed on electrode 120 of the electrode
assembly 21.
End effector 22 includes a second or lower jaw member 42 which
has an inner facing surface 47 which opposes inner facing surface 45.
Preferably, jaw members 42 and 44 are dimensioned generally symmetrically,
however, in some cases it may be preferable to manufacture the two jaw
members 42 and 44 asymmetrically depending upon a particular purpose. In
much the same fashion as described above with respect to jaw member 44, jaw
member 42 also includes a plurality of mechanical interfaces or sockets 43
disposed thereon which are dimensioned to releasable engage a complimentary
portion 112 disposed on electrode 110 of the electrode assembly 21 as
described
below. Likewise, jaw member 42 also includes an aperture 65 disposed at least
partially through inner face 47 which is dimensioned to receive a
complimentary
guide pin 127 (see Fig. 4) disposed on electrode 110 of the electrode assembly
21.
Preferably, the end effectors 22, 24 (and, in turn, the jaw members
42 and 44 and the corresponding electrodes 110 and 120) are disposed at an
angle alpha (a) relative to the distal ends 19, 17 (See Fig. 2). It is
contemplated
that the angle alpha (a) is in the range of about 50 degrees to about 70
degrees
relative to the distal ends 19, 17. It is envisioned that angling the end
effectors
22, 24 at an angle alpha (a) relative to the distal ends 19, 17 may be
advantageous for two reasons: 1) the angle of the end effectors, jaw members
and electrodes will apply more constant pressure for cutting and/or for a
constant
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tissue thickness at parallel for sealing purposes; and 2) the thicker proximal
portion of the electrode, e.g., 110, (as a result of the taper along width
"W") will
resist bending due to the reaction force of the tissue 150. The tapered "W"
shape
(Fig. 2) of the electrode 110 is determined by calculating the mechanical
advantage variation from the distal to proximal end of the electrode 110 and
adjusting the width of the electrode 110 accordingly. It is contemplated that
dimensioning the end effectors 22, 24 at an angle of about 50 degrees to about
70 degrees is preferred for accessing and activating specific anatomical
structures relevant to prostatectomies and cystectomies, e.g., the dorsal vein
complex and the lateral pedicles.
Preferably, shaft members 12 and 14 of the mechanical forceps 20
are designed to transmit a particular desired force to the opposing inner
facing
surfaces of the of the jaw members 22 and 24, respectively, when clamped or
during sealing and/or cutting. In particular, since the shaft members 12 and
14
effectively act together in a spring-like manner (i.e., bending that behaves
like a
spring), the length, width, height and deflection of the shaft members 12 and
14
will directly effect the overall transmitted force imposed on opposing jaw
members
42 and 44. Preferably, jaw members 22 and 24 are more rigid than the shaft
members 12 and 14 and the strain energy stored in the shaft members 12 and 14
provides a constant closure force between the jaw members 42 and 44.
Each shaft member 12 and 14 also includes a ratchet portion 32
and 34, respectively. Preferably, each ratchet, e.g., 32, extends from the
proximal end 13 of its respective shaft member 12 towards the other ratchet 34
in
a generally vertically aligned manner such that the inner facing surfaces of
each
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ratchet 32 and 34 abut one another when the end effectors 22 and 24 are moved
from the open position to the closed position. Each ratchet 32 and 34 includes
a
plurality of flanges 31 and 33, respectively, which project from the inner
facing
surface of each ratchet 32 and 34 such that the ratchets 32 and 34 can
interlock
in at least one position. In the embodiment shown in Fig. 1, the ratchets 32
and
34 interlock at several different positions. Preferably, each ratchet position
holds
a specific, i.e., constant, strain energy in the shaft members 12 and 14
which, in
turn, transmits a specific force to the end effectors 22 and 24 and, thus, the
electrodes 120 and 110. This is particularly relevant during sealing.
In some cases it may be preferable to include other mechanisms to
control and/or limit the movement of the jaw members 42 and 44 relative to one
another. For example, a ratchet and pawl system could be utilized to segment
the movement of the two handles into discrete units which will, in turn,
impart
discrete movement to the jaw members 42 and 44 relative to one another.
Preferably, at least one of the shaft members, e.g., 14, includes a
tang 99 which facilitates manipulation of the forceps 20 during surgical
conditions
as well as facilitates attachment of electrode assembly 21 on mechanical
forceps
20 as will be described in greater detail below.
As best seen in Figs. 2, 3 and 5, one embodiment of the
electrosurgical instrument includes electrode assembly 21 is designed to work
in
combination with mechanical forceps 20. Preferably, electrode assembly 21
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includes housing 71 which has a proximal end 77, a distal end 76 and an
elongated shaft plate 78 disposed therebetween. A handle plate 72 is disposed
near the proximal end 77 of housing 71 and is sufficiently dimensioned to
releasably engage and/or encompass handle 18 of mechanical forceps 20.
Likewise, shaft plate 78 is dimensioned to encompass and/or releasably engage
shaft 14 and pivot plate 74 disposed near the distal end 76 of housing 71 and
is
dimensioned to encompass pivot 25 and at least a portion of distal end 19 of
mechanical forceps 20. It is contemplated that the electrode assembly 21 can
be
manufactured to engage either the first or second members 9 and 11 of the
mechanical forceps 20 and its respective component parts 12, 16 or 14, 18,
respectively.
In the embodiment shown in Fig. 3, handle 18, shaft 14, pivot 25
and a portion of distal end 19 are all dimensioned to fit into corresponding
channels located in housing 71. For example, a channel 139 is dimensioned to
receive handle 18, a channel 137 is dimensioned to receive shaft 14 and a
channel 133 is dimensioned to receive pivot 25 and a portion of distal end 19.
Electrode assembly 21 may also includes a cover plate 80 which is
designed to encompass and/or engage mechanical forceps 20 in a similar
manner as described with respect to the housing 71. More particularly, cover
plate 80 includes a proximal end 85, a distal end 86 and an elongated shaft
plate
88 disposed therebetween. A handle plate 82 is disposed near the proximal end
85 and is preferably dimensioned to releasable engage and/or encompass handle
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18 of mechanical forceps 20. Likewise, shaft plate 88 is dimensioned to
encompass and/or releasable engage shaft 14 and a pivot plate 94 disposed near
distal end 86 is designed to encompass pivot 25 and distal end 19 of
mechanical
forceps 20. Preferably, handle 18, shaft 14, pivot 25 and distal end 19 are
all
dimensioned to fit into corresponding channels (not shown) located in cover
plate
80 in a similar manner as described above with respect to the housing 71.
As best seen with respect to Figs. 3 and 4, housing 71 and cover
plate 80 are designed to engage one another over first member, e.g., 11, of
mechanical forceps 20 such that first member 11 and its respective component
parts, e.g., handle 18, shaft 14, distal end 19 and pivot 25, are disposed
therebetween. Preferably, housing 71 and cover plate 80 include a plurality of
mechanical interfaces disposed at various positions along the interior of
housing
71 and cover plate 80 to effect mechanical engagement with one another. More
particularly, a plurality of sockets 73 are disposed proximate handle plate
72,
shaft plate 78 and pivot plate 74 of housing 71 and are dimensioned to
releasably
engage a corresponding plurality of detents (not shown) extending from cover
plate 80. It is envisioned that either male or female mechanical interfaces or
a
combination of mechanical interfaces may be disposed within housing 71 with
mating mechanical interfaces disposed on or within cover plate 80.
As best seen with respect to Figs. 5-7A, the distal end 76 of
electrode assembly 21 is bifurcated such that two prong-like members 103 and
105 extend outwardly therefrom to support electrodes 110 and 120,
respectively.
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More particularly, electrode 120 is affixed at an end 90 of prong 105 and
electrode 110 is affixed at an end 91 of prong 103. It is envisioned that the
electrodes 110 and 120 can be affixed to the ends 91 and 90 in any known
manner, e.g., friction-fit, slide-fit, snap-fit engagement, crimping, etc.
Moreover, it
is contemplated that the electrodes 110 and 120 may be selectively removable
from ends 90 and 91 depending upon a particular purpose and/or to facilitate
assembly of the electrode assembly 21. As mentioned above, the inventive
concepts disclosed herein may also relate to an electrosurgical instrument
which
does not include a selectively detachable electrode assembly, but, rather,
includes end effectors which have integrally associated electrodes disposed
thereon.
A pair of wires 60 and 62 are connected to the electrodes 120 and
110, respectively, as best seen in Figs. 4 and 5. Preferably, wires 60 and 62
are
bundled together and form a wire bundle 28 (Fig. 4) which runs from a terminal
connector 30 (see Fig. 3), to the proximal end 77 of housing 71, along the
interior
of housing 71, to distal end 76. Wire bundle 28 is separated into wires 60 and
62
proximate distal end 76 and the wires 60 and 62 are connected to each
electrode
120 and 110, respectively. In some cases it may be preferable to capture the
wires 60 and 62 or the wire bundle 28 at various pinch points along the inner
cavity of the electrode assembly 21 and enclose the wires 60 and 62 within
electrode assembly 21 by attaching the cover plate 80.
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This arrangement of wires 60 and 62 is designed to be convenient
to the user so that there is little interference with the manipulation of
bipolar
forceps 10. As mentioned above, the proximal end of the wire bundle 28 is
connected to a terminal connector 30, however, in some cases it may be
preferable to extend wires 60 and 62 to an electrosurgical generator (not
shown).
As best seen in Fig. 6, electrode 120 includes an electrically
conductive surface 126 and an electrically insulative substrate 121 which are
attached to one another by snap-fit engagement or some other method of
assembly, e.g., slide-fit, overmolding of a stamping or metal injection
molding.
Preferably, substrate 121 is made from molded plastic material and is shaped
to
mechanically engage a corresponding socket 41 located in jaw member 44 of end
effector 24 (see Fig. 2). The substrate 121 not only insulates the electric
current
but it also aligns electrode 120 both of which contribute to the reduction of
thermal
spread across the tissue and a reduction of the incidence of flashover.
Moreover, by attaching the conductive surface 126 to the substrate 121
utilizing
one of the above assembly techniques, the alignment and thickness, i.e.,
height
"h2", of the electrode 120 can be controlled. For example and as best
illustrated
in the comparison of Figs. 7B and 7C , the overmolding manufacturing technique
reduces the overall height "h2" (Fig. 7C) of the electrode 120 compared to
traditional manufacturing techniques which yield a height of "h1" (Fig. 7B).
The
smaller height "h2" allows a user access to smaller areas within the body and
facilitates activation around more delicate tissue areas.
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Moreover, it is contemplated that the overmolding technique
provides more insulation along the side of the electrically conductive surface
which also reduces thermal spread due to less electrode to tissue contact. It
is
envisioned that by dimensioning substrate, e.g., 121 and electrode 120 in this
fashion (i.e., with reduced conductive surface area), the current is
restricted
(i.e., concentrated) to the intended area rather than current traveling to
tissue
outside the intended area which may come into contact with an outer edge of
the electrode 120 (see Fig. 7B). Providing more insulation along the side of
the
electrically conductive surface may also effectively reduce the incidence of
flashover.
Preferably, substrate 121 includes a plurality of bifurcated detents
122 which are shaped to compress during insertion into sockets 41 and expand
and releasably engage sockets 41 after insertion. It is envisioned that snap-
fit
engagement of the electrode 120 and the jaw member 44 will accommodate a
broader range of manufacturing tolerances. Substrate 121 also includes an
alignment or guide pin 124 which is dimensioned to engage aperture 67 or jaw
member 44. A slide-fit technique is also contemplated such as the slide-fit
technique describe with respect to WIPO Publication No. WO 2002/080793 by
Tetzlaff et al.
Conductive surface 126 includes a wire crimp 145 designed to
engage the distal end 90 of prong 105 of electrode assembly 21 and
electrically
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engage a corresponding wire connector affixed to wire 60 located within
electrode
assembly 21. Conductive surface 126 also includes an opposing face 125 which
is designed to conduct an electrosurgical current to a tubular vessel or
tissue 150
when it is held thereagainst. It is envisioned that the conductive surfaces
126
(116) may be dimensioned as a sealing surface, a clamping surface and/or a
shearing or cutting surface depending upon a particular purpose.
Electrode 110 includes similar elements and materials for insulating
and conducting electrosurgical current to tissue 150. More particularly,
electrode
110 includes an electrically conductive surface 116 and an electrically
insulative
substrate 111 which are attached to one another by one of the above methods of
assembly. Substrate 111 includes a plurality of detents 112 which are
dimensioned to engage a corresponding plurality of sockets 43 and aperture 65
located in jaw member 42. Conductive surface 116 includes an extension 155
having a wire crimp 119 which engages the distal end 91 of prong 103 and
electrically engages a corresponding wire connector affixed to wire 62 located
in
housing 71. Conductive surface 116 also includes an opposing face 115 which
conducts an electrosurgical current to a tubular vessel or tissue 150 when it
is
held thereagainst. It is contemplated that electrodes 110 and 120 can be
formed
as one piece and include similar components and/or dimensions for insulating
and conducting electrical energy in a manner to effectively reduce thermal
spread
and the incidence of flashover. Stray current may be further restricted by
casting
the forceps and/or manufacturing the forceps using a non-conductive material
and/or coating the edges of the electrodes 110 and 120 with an insulative
coating.
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As mentioned above, it is envisioned that flashover and thermal
spread may be reduced by altering the physical dimensions (geometry/shape) of
the insulators and/or the chemical characteristics of the insulators. With
particular respect to thermal spread, it is envisioned that manufacturing the
electrodes 110 and 120 in this fashion will reduce thermal spread and stray
currents that may travel to the electrosurgical instrument. More particularly,
the
varying geometry of the insulator 111 compared to the electrically conductive
surface 116 also isolates the two opposing poles during activation thereby
reducing the possibility that tissue or fluids will bridge a path for stray
current
travel to surrounding tissue. With respect to flashover, altering the geometry
of
the insulator 11 and/or conductive surface creates a longer path for the
current to
travel over the insulator 111 before flashover occurs.
For example and as best shown in the comparison of Fig. 7B (prior
art) with newly disclosed Figs. 7C, 7D, 14A and 14B substrates 111, 121 are
designed to extend along width "W" (Fig. 2) such that the width of the
insulating
substrate, e.g., 111, exceeds the width of the electrically conductive
surface, e.g.,
116. It is envisioned that these electrically conductive surface 116 and
insulator
111 configurations may be accomplished by various manufacturing techniques
such as overmolding of a stamping and/or metal injection molding. Stamping is
defined herein to encompass virtually any press operation known in the trade,
including, but not limited to: blanking, shearing, hot or cold forming,
drawing,
bending and coining. Other manufacturing techniques may also be employed to
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achieve similar electrically conductive surface 116 and insulator 111
configurations which will effectively reduce thermal spread to adjacent
tissue.
As best seen in Fig. 7D, the electrode 116 may also include a pinch
trim 131 which facilitates secure, integral engagement of the insulate 111 and
the
electrically conductive surface 116 during the assembly and/or manufacturing
process. FIG. 7E shows another embodiment of the present disclosure wherein
a compliant material 161 is disposed about the outer peripheries of the
electrically
conductive surfaces 116, 126 and the substrates 111, 121. it is envisioned
that
the compliant material 161 acts as a mechanical barrier by restricting heat
and
steam emanating from the surface thereby reduces thermal spread to surrounding
tissue. One or more barriers 161 may be attached to the end effectors 22, 24
and/or the insulting substrate 111, 121 depending upon a particular purpose of
to
achieve a particular result.
Figs. 14A, 14B, 14C and 15 show the electrically conducive
surfaces 116, 126 raised relative to the insulative coatings or insulators
111, 121.
Preferably, the electrically surface 116, 126 is radiused or curved which
reduces
current concentration and the dissipation of stray currents to surrounding
tissue
structures. It is contemplated that the insulators 111, 121 and electrically
conductive surfaces 116, 126 can be dimensioned to meet at or generally along
interfaces or adjoining longitudinally-oriented edges 129, 139 which are
radiused
to reduce current concentrations 141 and current dissipation proximate the
interfaces 129, 139 and opposing electrically conductive surfaces 116, 126.
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For example and by way of illustration, Figs. 12 and 13A-13C show
other electrode 110, 120 configurations which are known in the prior art. Fig.
12
shows an example of uninsulated (i.e., without insulators 111, 121) opposing
electrodes 110, 120 during activation illustrating the electrical field
distribution 135
emanating from the opposing electrically conductive surfaces 116, 126 (it is
known that current flows perpendicular to these electrical field lines). As
can be
appreciated, the electrical field 135 emanates well beyond the intended
treatment
site which can contribute to increased collateral tissue damage and possibly
cutting.
By providing insulators 111, 121 which are flush with the electrically
conductive surfaces 116, 126 as shown in Figs. 13A-13C, the electrical field
distribution 135 can be significantly reduced. However, as the enlarged views
of
Figs. 13B and 13C illustrate, a current concentration 141 tends to develops
between opposing electrically conductive surfaces 116, 126 and at or proximate
interfaces 129, 139. This current concentration 141 may also lead to negative
effects and possibly cause cutting of the tissue or sticking of the tissue to
the
electrode or electrically conductive surfaces at this site.
Figs. 14A-15 show various electrode 110, 120 configurations
according to the present disclosure in which the electrically conductive
surfaces
116, 126 and the insulators 111, 121 are designed to reduce the amount of
current concentration 141 between opposing electrodes 110, 120. More
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particularly, Figs. 14A and 14B show a pair of raised electrically conductive
surfaces 116, 126 (relative to the insulators 111, 121) which include outer
peripheries 145, 147 having radii "r" and "r' ", respectively. Preferably,
insulators
111, 121 meet outer peripheries 145, 147 and form adjoining edges or
interfaces
129, 139 which track along radii "r" and "r' ", respectively. It is
contemplated that
configuring the electrodes 110, 120 in this manner will effectively reduce the
current concentration 141 between the outer peripheries 145, 147 of the
opposing
electrically conductive surfaces 116, 126. As can be appreciated, configuring
the
electrically conductive surfaces 116, 126 and insulators 111, 121 with this
unique
profile, additionally provides a more uniform, consistent and more easily
controllable electrical field distribution 135 across the adjacent tissue
structures.
Turning back to Fig. 7C, it is envisioned that insulator 111 may also meet
outer
periphery 145 in a generally tangential fashion about radius "r". Again, this
profile
also tends to reduce current concentration and thermal spread and may also
contribute to a reduction in the incidence of flashover.
Fig. 15 also shows the insulators 111, 121 and the electrically
conductive surfaces 116, 126 meeting at an angle of ninety degrees (90 ),
however, the insulator 111, 121 is positioned further from the radiused edge
145
of the electrically conductive surface 116, 126 . It is envisioned that too
much
exposure of the edge 145 may initiate the formation of new and/or additional
stray
currents or electrical fields proximate the interface 129, 139 thereby
nullifying the
benefits of manufacturing the surface 116, 126 with a radiused edge 145.
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Preferably, the radius "r" and "r' " of the outer peripheries 145, 147
of the electrically conductive surfaces are about the same and are about ten
thousandths of an inch to about thirty thousandths of an inch. However, it is
contemplated that each radii "r" and "r' " may be sized differently depending
upon
a particular purpose or to achieve a desired result.
Although it is contemplated that geometric modification of the
insulator 111 relative to the electrically conductive sealing surface 116
reduces
the incidence of flashover and thermal spread, in some cases it may be
preferable to simply utilize a different material for the insulator to reduce
flashover
and thermal spread. For example and with particular respect to flashover, it
is
known that all plastics have a different resistance to flashover which is
commonly
measured using a Comparative Tracking Index (CTI). The CTI value required to
resist flashover is typically dictated in part by the maximum voltage of the
electrosurgical generator, however, other parameters such as frequency also
typically effect flashover.
It has been found that in lieu of or in addition to changing the
geometry of the insulator 111 and/or conductive surface 116, a plastic
insulation
can be employed having a CTI value of about 300 to about 600 volts. Examples
of high CTI materials include nylons and syndiotactic polystryrenes such as
QUESTRA manufactured by DOW Chemical. Other materials may also be
utilized either alone or in combination to reduce flashover, e.g., Nylons,
Syn d iota ctic-polystryre ne (SPS), Polybutylene Terephthalate (PBT),
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Polycarbonate (PC), Acrylonitrile Butadiene Styrene (ABS), Polyphthalamide
(PPA), Polymide, Polyethylene Terephthalate (PET), Polyamide-imide (PAI),
Acrylic (PMMA), Polystyrene (PS and HIPS), Polyether Sulfone (PES), Aliphatic
Polyketone, Acetal (POM) Copolymer, Polyurethane (PU and TPU), Nylon with
Polyphenylene-oxide dispersion and Acrylonitrile Styrene Acrylate.
In some cases, however, it may be preferable to alter both the
geometry of the insulator 111 and/or conductive surface 116 and/or utilize a
plastic insulation that does not have a CTI value of about 300 to about 600
volts.
Alternatively, certain coatings can be utilized either alone or in combination
with
one of the above manufacturing techniques to reduce flashover and thermal
spread.
Fig. 8A shows one embodiment of the present disclosure which
shows a bipolar forceps 10 during use wherein the handle members 16 and 18
are moved closer to one another to apply clamping force to the tubular tissue
150
to effect a seal 152 as shown in Figs. 9 and 10. Once sealed, the tubular
vessel
150 can be cut along seal 152 to separate the tissue 150 and form a gap 154
therebetween as shown in Fig. 11. Alternatively, the electrically conductive
surfaces 116, 126, electrodes 110, 120 and/or the jaw members 42, 44 may be
dimensioned as shearing surfaces which effectively cut the tissue when the jaw
members 42, 44 are moved relative to one another.
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After the bipolar forceps 10 is used or if the electrode assembly 21
is damaged, the electrode assembly 21 can be easily removed and/or replaced
and a new electrode assembly 21 may be attached to the forceps in a similar
manner as described above. It is envisioned that by making the electrode
assembly 21 disposable, the electrode assembly 21 is less likely to become
damaged since it is only intended for a single operation and, therefore, does
not
require cleaning or sterilization. As a result, the functionality and
consistency of
the components, e.g., the electrically conductive surfaces 126, 116 and
insulating
surfaces 121, 111, will assure a reliable reduction of thermal spread across
tissue
and/or reduce the incidence of flashover. Alternatively, the entire
electrosurgical
instrument may be disposable which, again, may contribute to a reduction of
thermal spread across tissue and/or reduce the incidence of flashover
Fig. 8B shows an endoscopic bipolar instrument 100 during use
wherein movement of a handle assembly 128 applies clamping force on the
tubular tissue 150 to effect a seal 152 as shown in Figs. 9-11. As shown, a
shaft
109 and the electrode assembly 122 are inserted through a trocar 130 and
cannula 132 and a handle assembly 118 is actuated to cause opposing jaw
members of the electrode assembly 122 to grasp tubular vessel 150
therebetween. More particularly, a movable handle 11 8b is moved progressively
towards a fixed handle 11 8a which, in turn, causes relative movement of the
jaw
members from an open, spaced-apart position to a closed, activation position.
A
rotating member 123 allows the user to rotate the electrode assembly 122 into
position about the tubular tissue 150 prior to activation. Again, the
electrically
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conductive surfaces 116, 126, electrodes 110, 120 and/or the jaw members 42,
44 may be dimensioned as shearing surfaces which effectively cut the tissue
when the jaw members 42, 44 are moved relative to one another.
After the jaw members are closed about the tissue 150, the user
then applies electrosurgical energy via connection 128 to the tissue 150. By
controlling the intensity, frequency and duration of the electrosurgical
energy
applied to the tissue 150, the user can either cauterize, coagulate/desiccate,
seal,
cut and/or simply reduce or slow bleeding with minimal collateral or thermal
damage to surrounding tissue and with minimal incidence of flashover.
From the foregoing and with reference to the various figure
drawings, those skilled in the art will appreciate that certain modifications
can also
be made to the present disclosure without departing from the scope of the
present
disclosure. For example, although it is preferable that electrodes 110 and 120
meet in parallel opposition, and, therefore, meet on the same plane, in some
cases it may be preferable to slightly bias the electrodes 110 and 120 to meet
each other at a distal end such that additional closure force on the handles
16
and 18 is required to deflect the electrodes in the same plane.
It is envisioned that the outer surface of the end effectors may
include a nickel-based material, coating, stamping, metal injection molding
which
is designed to reduce adhesion between the end effectors (or components
thereof) with the surrounding tissue during activation.
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While only one embodiment of the disclosure has been described, it
is not intended that the disclosure be limited thereto, as it is intended that
the
disclosure be as broad in scope as the art will allow and that the
specification be
read likewise. Therefore, the above description should not be construed as
limiting, but merely as exemplifications of a preferred embodiment. Those
skilled
in the art will envision other modifications within the scope and spirit of
the claims
appended hereto.
