Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates -to electrosur~ical
dispersive electrodes. More specifically, the present
invention relates to an electrode for attachment to a
patient's skin with connections to an electrosurgical
S generator.
Electrosurgical dispersive electrodes available
on the market today take many shapes, forms and sizes. Such
electrodes are used -to return current from a patient's skin
to an electrosurgical generator during electron surgery which
involves cutting, coagulation or a blend of these two
techniques. Electrosurgical electrodes must have good
adhesive quality to stick to the skin and to stay on the
skin during the entire surgery process. The distribution
of current flow through the conductive surface of the
electrode is a factor which relates to the temperature rise
under the electrode. It has been found that current flow
is generally not uniform and therefore hot areas occur on
a patient's skin under the conductive surface of -the elect-
rode. Many electrodes use gel, mostly a high conductive gel,
however some of these gels -tend to migrate, that is to say
move so that an uneven thickness of gel occurs across the
conductive surface which again leads to a non-uniform
temperature on the patients skin. Gel also can migrate
to the adhesive portion of the electrode which reduces the
adhesive properties, often resulting in the electrode not
properly contacting the patient's skin.
Most electrodes presently available on the market
today are constructed of an insulating material on which a
metallic surface has been attached. In some cases the
electrodes have gel which covers the metallic surface. The
peripheral portion of the electrodes where there is no gel
usually contains an adhesive material which holds the elect-
rode -to the patient's skin. Some electrodes use a conductive
adhesive gel throughout their entire surface area. In some
cases, gel is applied to a dry metal surface on the conductive
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area just before attaching the electrode to the patient's
skin.
It has been found that a higher current occurs
at the outer periphery of the conductive surface on the
electrode and this is where heat is produced on the skin.
The result is a substantially higher temperature at this
peripheral edge which can in certain circumstances cause a
burn on the patient's skin.
One electrode design available on the market today
is made of a dry non-conductive material, usually a gauze or a foam
type material under which is a conductive metallic surface.
The peripheral portion of the electrode consists of an ad-
hesive material and the current returns via a capacitive
coupling and is distributed more uniformly over the entire
surface area of the patient. The electrode field between
the electrode and the patient is more uniform than with other
types of electrodes. Elowever this electrode contains an
inherent hazard: if a small hole or pinhole defect occurs
in the electrode surface, then the current can concentrate
at this spot and cause a burn on the patient's skin.
We have found that these problems of varying heat
from the surface area of an electrosurgical electrode can be
overcome by providing divided sections of conductive surface,
each section being connected to a separate resistor whose
value determines the proportion of current allowed to flow
through i-t. By choosing different resistance values, the
current may be distributed more evenly throughout -the entire
electrode conductive surface. This electrode requires the
sections to be spaced apart a sufficient amount to avoid
problems occurring with short circuiting across adjacent
sections, as this defeats the purpose of dividing the con--
ductile surface into different sections.
It is an object of the present invention to
provide an electrosurgical electrode with a uniform current
I, 35 distribution and therefore a uniform heat distribution over
the conductive surface of the electrode. It is a further
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object to produce an electrode that provides both a lower
current density and a lower heat density at the contact with
the patient's skin thrill present designs of electrosurgical
electrodes.
the present invention provides an electrode for corn-
ectlon to an electrosurgical generator comprising: a pour-
` amity of separate conductive elements spaced apart in a
; surface plane and attached to a non-conductive backing, a
connector from each one of the conductive elements to a
lo resistor having a resistance value proportional to current
flow through the one of the conductive elements to provide
uniform current distribution, and attachment means for attach-
in the conductive elements to a patients skin.
In other embodiments of the invention, a gel coating
is included on the conductive elements, the gel coating
having a high resistivity. The conductive elements in another
embodiment are in the form of a plurality of concentric rings
about a circular disc, with the disc and each of the rings
being connected -to individual resistors having different
resistance values, such that current density per skin surface
I` contact area is substantially the same for the disc and the
rings. In a preferred embodiment each of the resistors for
` the concentric rings on the outside has a higher resistance
I` value than the resistors for the concentric rings on the in-
side and the disc. Preferably the conductive elements each
have a resistor with a resistance value no-t greater than about
50 ohms. In another embodiment, the conductive elements are
in the form of parallel strips with a spacing of at least
about 2 mm provided between the strips. The gel coating pro-
fireball has a gel resistivity in the range of about S00 to
`; l,000 ohm-centimetres. In a still further embodiment, the
electrode and connectors include a short cable and polarized
I` connector plug which are all disposable, the connector plug
is adapted to mate with a socket having connections to the
resistors and elec-trosurgical generator.
In jet a further embodiment, the circular disc
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has a connector link in the same plane as the skin surface
contact area extending off to one side, and wherein each of
the ~ncentricrinys has a peripheral gap and a connector link
in the same plane as the skin surface extending off pi the one
side, wherein the connector links from the disc and each
rlncJ are substantially parallel to each other and extend off
to the one side thigh the peripheral gaps in adjacent larger
centric rings. A shorting pad may be provided adjacent the
connectors, adapted to cooperate with a separate continuity
connector to indicate a completed connection between the
electrode and the electrosurgical generator.
In other embodiments, the non conductive backing
is a plastic sheet and the attachment means includes an
adhesive material contained in a peripheral portion surround-
in the conductive elements. The non conductive gaps between
conductive elements may also have adhesive material therein
or alternatively the gel coating may be an adhesive gel to
form the attachment means, -the adhesive gel having a high
resist:ivity.
In drawings which illustrate embodiments of the
invention,
Fig. 1 is a schematic perspective view of a
patient having an electrode of the present invention attached
Jo a thigh and connected to an electrosurgical generator.
Fig. 2 is a schematic view of an electrode of the
present invention with a polarized connector plug for
connection to a socket.
Figs. 3, 4 and S are plan views showing different
embodiments of electrodes according to the present invention.
Fig. 1 illustrates -the use of an electrode for
electrosurgery and shows a patient 10 having an electrode
11 attached to a thigh. A multiple cable 12 connects the
different elements of the electrode 11 to a polarized
; connector plug 13 which in turn is connected -to a socket 1
having a permanent cable lo leading to a resistor box 16.
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The resistor box 16 has a connecting gable 17 leading to
the electrosurgical generator 18. The resistor box 16
may form part of the electrosurgical generator 18. Upon
completion o-E electrosurgery, the cable 12 together with
electrode 11 and plug 13 are disposed of end not reused
whereas the socket 15 with -the permanent cable 15 to the
resistor box 16 can be used a number of times. The electron
; surgical generator 18 is a conventional device comprising a
; high frequency current generating system including an RF
oscillator which drives a gain controlled power amplifier that is coupled via a step-up transformer and coupling
capacitors to the active electrode 19. The active electrode
19 may be in the form of a knife, scalpel or other implement
dependent upon the particular type of electrosurgery being
; 15 performed.
One example of -the electrode 11 is shown in Fig.
2 having two concentric circular elements 20, 21 about a
center circular element 22. The elements 20, 21 and 22 are
mounted on a non-conductive circular backing 23 having a
gap between each element and an exterior peripheral portion
-to which an adhesive is attached for securing -the electrode
11 to a patient's skin. Three connector wires 24 from the
three elements 20, 21 and 22 pass through the cable 12 to the
polarized connector plug having three prongs 25 which engage
with sockets 26 in the plug 14. Resistors 27 in the resistor
box 16 have a predetermined resistance value for a particular
element 20, 21 and 22. Beyond the three resistances 27,
-I the wires are connected together to have one lead in the
cable 17 to the electrosurgical generator 18. A second lead
may be included in the cable 17 as a continuity check between
the electrode and the generator 18. The resistance value is
determined so as to have uniform temperature distribution
and this is obtained by having uniform current density per
Jo skin surface contact area for the electrode 11. The surface
Jo 35 area of each element is determined and then -the portion of
the total current to each element is calculated. With this
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figure, the resistance value for each resistor 27 is
determined. It is preferable that the values of these
resistors do not exceed 50 ohms, however the resistance
values are determined for use with a gel having a known
resistance. A 50 ohm r~sistivity would would be suitable
with a gel having a resistivity in the range of about 500
to 1,000 ohm centlmetres.
As current normally flows at the periphery of
the electrodes, the resistors for the outer rinks have a
higher resistance value than those in the center. This
forces -the current to be distributed more evenly throughout
the entire conductive surface of the electrode. The rings
are separated by a gap which is normally at least about 2
mm in width. The gap is sufficient for the resistor circuit
to be effective and to prevent short circuiting of the three
elements 20, 21 and 22.
Figs. 3 and 4 illustrate electrodes 11 with con-
nitric elements. Fig. 3 has a center circular disc 30 having connector link 31 to a connector tab 32. An intermediate
centric rink element 33 has a peripheral gap 34 for passage
of the connector link 31 from the disc 30 and has a second
connector link 35 to the connector tab 32. on outside con-
centric ring element 36 has a further peripheral gap 37 for the
two connector links 31 and 35 and a third connector link 38
to the connector tab 32. The connector links 31, 35 and 38
are substantially parallel and all lead out to one side of
the electrode passing through the peripheral gaps 34 and 37.
The elements 30, 33 and 36 are all in the same plane and have
gaps between each other of about 2 mm. The elements
are mounted on a non-conductive backing material 39 which has
a peripheral portion 40 containing an adhesive material. The
backing material 39 may be foam, plastic, fabric or other
suitable sheet material that is non-conductive. The adhesive
which is preferably non-conductive, extends across the
connector tab 32 to ensure that the connector links 31, 35
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and 38 are not in contact with the skin surface.
A similar embodiment is shown in Fig. with a
center circular disc 30 and five concentric ring elements
I extending out from the clement with connector links I
to a connector tab 32. The embodiments shown in Fig. 3 has
a diameter of approximately 9 centimeters whereas the die-
meter of -the electrode shown in Fig. 4 is approximately 16
centimeters. The smaller unit shown in Fig. 3 is designed
as a pediatric model, whereas the larger unit is for adult
applications. The conductive medium for the elements is a
metallic sheet such as aluminum, stainless steel, copper or
other suitable material. A non-metallic conductive sheet
material may also be applicable with a thickness in the order
of approximately 1 mix mounted on a suitable non-conductive
backing sheet. As shown, the tab 32 has a shorting pad I
for connection to a continuity circuit. This shorting pad
I completes a check circuit between the electrode and the
generator to indicate that the system is properly connected.
Whereas two embodiments are shown herein, it will be under-
stood -that other electrodes having a different number of ring
elements may be produced dependent upon the particular
requirement of -the electrode.
` In a preferred embodiment, a coating of gel is
placed on the conductive surfaces of the electrode. The gel
cannot be highly conductive as compared to metal or a saline
solution, otherwise short circuiting occurs between adjacent
` elements which defeats the purpose of the electrode. A
gel with a higher resistivity is required. A gel having a
resistance in the range of about 500 to 1,000 ohm-centimetres
is appropriate as it has a higher value than the resistors
used to control the flow of current through the different
elements and therefore has minimal influence on the current
flowing ability of the electrode. This higher resistivity
gel provides a better patient electrode contact and an
intermediate impedance value that contributes to a more unit
form electrical field between the patient's skin and the
I- electrode.
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One -type of vet that has been found suitable
is a purified ajar gel in solid form. The gel unwell those
made with a bacteriological grade of ajar is highly
resistive thus providing ideal resistivlty between the
skin and the electrode and avoiding short circuiting that
could occur with a normal gel which would result in non-
uniform current distribution.
Whereas an adhesive is attached to the peripheral
portion 40 of the backing material, in some cases adhesive
may be included in -the gaps between the elements to ensure
good con-tact and to maintain the conductive surface of -the
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adhesive gel may be utilized across the surface of the elect-
rode including the surface of the conductive elements,
however such a gel must have high resistivity to prevent short
circuiting.
I, Fig. 5 illustrates a rectangular shaped electrode
11 having parallel strip elements 60 with small gaps there-
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61 to form -the main cable 12.
Various changes may be made -to the embodiments
shown without departing from the scope of the present invention
which is limited only by the following claims.
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