FR2459039A1 - INDIFFERENT OR PASSIVE ELECTRODE WITH CAPACITIVE COUPLING - Google Patents

Abstract

ELECTRODE 10 USED IN ELECTROSURGERY. IT INCLUDES A SUBSTRATE 12, A METAL SHEET 14 CONDUCTING ELECTRICITY AND GLUED TO A SURFACE OF THE BUFFER FORMING THE SUBSTRATE, A LAYER OF INSULATING MATERIAL 16 FULLY COVERING THE METAL SHEET AND A LAYER OF PRESSURE SENSITIVE ADHESIVE 20 COVERS THE INSULATION LAYER. THIS ELECTRODE IS PLACED ON THE SKIN OF A PATIENT AND CAN BE CONNECTED TO THE RETURN TERMINAL OF AN ELECTROSURGERY GENERATOR BY MEANS OF A CABLE WHICH IS CONNECTED THROUGH THE SUBSTRATE TO THE ELECTRODE.

Description

1. 2459039

  The invention relates to electrodes used in medicine, more particularly to passive or indifferent electrodes used in electrosurgery and in particular to a capacitively coupled electrode whose convenience, safety and performance are improved. In electrosurgery, a generator produces a strong high frequency electric current that is sent to an active electrode. It is used to cut tissue and coagulate blood vessels and is energized for relatively short periods of time during these operations. An indifferent or passive electrode which is placed on the patient is brought into contact with the latter in order to produce a return circuit of the high frequency current towards the generator which, for its part, is connected for example directly to the mass or to an element isolated forming

the mass.

  The input current is applied to the tissues by the active electrode which preferably has a small cross section so that it is possible to obtain high current densities at the location at which the operation takes place. These high current densities provide the necessary heating (i.e., temperatures up to 1000C at the point of contact) required to perform the operation. It is essential, however, that the passive or indifferent electrode be in sufficient contact with the patient to ensure that the current return is low density so as to avoid burns or scarring on the patient's tissue.

  which is in contact with the indifferent electrode.

  The indifferent or passive electrodes of the prior art have been either of the direct electrical contact type or of the capacitively coupled type type. Passive electrodes of the direct electrical contact type have either been designed to be directly attached or placed under a patient and have been available either in dry form (i.e., in direct metallic contact with the skin) or in form using a conductive gel or an adhesive (under

  electrode form bound to the skin by a conductive solution

  2. trice, gel or polymer). However, the electrodes of

  direct contact type raise different problems

  my. For example, when the electrode is used in previously gel-coated form, the gel may have dried before being used or may dry during the surgical procedure, bacteriological growth may occur in the gel and more, problems can arise for

  clean the patient to remove the gel after the operation.

  Moreover, the gel can be the cause of irritation of the

0 skin of some patients.

  When an electric contact type electrode

  direct is used in dry form, usually in the form of a plate or sheet of metal with a large surface area,

  other problems arise. These include the possibi-

  burns caused by the preferential paths followed by the current and the presence of which is due to perspiration of the patient or fluid projections at the location of the contact, or burns caused by the movements of the patient during the operation, movements that break contact with a significant part of the metal surface, and the risk that electrical current

  run to the doctors and the rest of the opera-

  in the event of accidental contact with an edge protruding from the metal electrode or contact with other surfaces

of the operating room.

  In addition, all types of passive or indifferent electrodes with direct electrical contact mode have had the disadvantage of revealing. hot spots around their outer edges due to the tendency of the high frequency electric current to leave the patient's body at these points. This irregularity of the current distribution

  the electrode increases the risk of burns or

  scars on the patient's skin.

  On the other hand, the capacitively coupled electrodes have the advantage of being much safer in use. Electrodes of this type comprise an insulating material placed between the metal electrode and the skin of the patient. These electrodes of the prior art have been maintained in place on

3. 2459039

  the patient's skin with elastic bands, pieces of tape or an adhesive placed around the edge of the

  capacitor structure. However, these prior methods

  Electrode fixation to the patient is unreliable. When a patient moves or changes position, air gaps or blisters cause some parts of the insulating material to move away from the patient's skin creating hot spots and raising the risk of causing burns or scars in the tissues. It would therefore be useful to have a passive or indifferent electrode for electrosurgery that

  is convenient to use, safe and reliable.

  The capacitively coupled electrode according to the invention

  includes a sheet of metal or other conductive material

  electricity which is mounted on cellular material

  laire or other suitable flexible material. According to an embodiment according to the invention, the electrical contact is produced by a metal rivet which passes through the metal sheet and the foam pad to reach the opposite side of the latter on which it is fixed in a metal sleeve which is then crimped so as to grip and hold the rivet. The metal sleeve can then be plugged with elastic restraint on an electric cable which,

  for its part, is connected to the return circuit of a genera-

  current transducer for electrosurgery. In an alternative embodiment, an electric cable and a plug can be

  previously fixed to the electrode.

  The metal foil is completely covered

  of a layer of insulating material, for example

  phthalate of polyethylene, polyvinylidene chloride, polyethylene or polysulfone. According to an advantageous embodiment, the insulating material is coated on both surfaces of a pressure-sensitive adhesive. In an alternative embodiment, the adhesive may be deposited during an independent operation during manufacture. The adhesive is intended to tightly attach the insulating material to the metal foil and when a removable, peelable cover sheet is removed, it is intended to tightly attach the electrode to the skin of a patient. Following a

  another variant embodiment, an insulating material metal-

  can be used in such a way as to eliminate the need

  adhesive between the insulating material and the metal foil

  league. To use this electrode, detach the removable cover protective sheet, and then place the composite electrode in place on the patient with the adhesive facing him. This adhesive prevents the formation of voids or voids and ensures the continuous contact of the insulating material on the entire surface of the electrode by performing a uniform electrical coupling with the skin. The shape of the composite electrode does not matter, this electrode can be produced in different forms, each of which is intended to be attached to a different part of the body of a patient. The electrode has for example a rectangular shape. The invention thus relates to a passive electrode

  or perfected indifferent which is intended to be used

  electrosurgery, which is safer to handle and

  which is more reliable than the electrodes of the prior art.

  The invention will be described in more detail in

  with reference to the drawings annexed to the title of example, which is in no way

  in which: - Figure 1 is an exploded perspective view

  of an embodiment of a passive or inductive electrode

  ferent according to the invention; FIG. 2 is a cross section of the assembled electrode; FIG. 3 is a graph showing the variation of the skin temperature as a function of the surface area of the capacitively coupled passive electrode; on the curve, a black triangle gives the value of a commercially available direct coupled passive electrode comprising a gel pad of 77.5 cm 2 of surface and a black square gives the value of an electrode of this type comprising a gel pad of 155 cm2 surface, while the white circles give the values of the electrode according to

5. 2459039

  the invention with an insulating layer, each white circle placed in the middle of a vertical line giving an average value and the vertical line representing the corresponding range of values; FIG. 4 is a graph showing the variation of the skin temperature as a function of the thickness of the insulating layer of a capacitively coupled electrode with an area of 193.5 cm 2; FIG. 5 is a graph representing the impedance as a function of the capacitively coupled electrode area, rectangles and triangles giving the values of two indifferent coupling electrodes;

  direct, commercially available, for the purpose of

  reason; FIG. 6 is a graph showing the path of the alternating current as a function of the area of the capacitively coupled electrode; FIG. 7 is a graph of the impedance as a function of the thickness of the insulating layer of a capacitively coupled electrode with an area of 193.5 cm 2; and FIG. 8 is a graph of the path of the alternating current as a function of the thickness of the layer

  insulation of a capacitively coupled electrode of a super-

193.5 cm2.

  Figures 1 and 2 show an indifferent or passive electrode 10 capacitively coupled. Although the electrode shown is rectangular, it has been observed that the shape of the electrode does not matter and can have different shapes. The electrode comprises a resilient and resilient backing layer 12, a metal sheet 14, a sheet of insulating material 16 and a protective cover sheet 18 on the surface of which is a coating for detaching it. One surface of the support material 12 is covered with a layer of medical grade, pressure sensitive, commercially available acrylic adhesive. The metal sheet 14 is then attached to the adhesive 20. The sheet 14 and the substrate 12 are then pierced by a metal rivet 22 comprising a

6. 2459039

  rod 24 of sufficient length to allow it to pass through the sheet 14 and the substrate 12, this rod having a shape complementary to that of a metal sleeve 26 to produce a circuit conducting electricity through the buffer. The sleeve 26 is then crimped so as to secure the rod in its place. The socket 26 can then be easily plugged with elastic restraint into a socket of a return wire of an electrosurgical generator. It is possible to alternatively use any suitable means for making a conductive path of

  electricity from layer 14 towards the return of a genera-

trice for electrosurgery.

  A wafer 28 of non-electrically conductive material, for example "nylon" or other insulating material is interposed between the rivet 22 and the insulating layer 16 to ensure that the rivet never comes into direct contact with the skin. of the patient. The insulating layer 16 may be any suitable non-electrically conductive material which can easily be formed into a thin film and may be of polyethylene, polyvinyl chloride, polyethylene terephthalate or polysulfone. The most advantageous insulating materials are polyethylene terephthalate available under the

  trademark "Mylar" and sold by E.I.

  DuPont de Nemours and Co., as well as polyvinyl chloride

  lidene available under the trade name "Saran" and which is sold by Dow Chemical Co. These materials are soft and strong and can be formed into films as thin as 12.5 pim. The insulating layer 16 is coated on both surfaces with a suitable pressure-sensitive adhesive and is then placed on the metal sheet 14. It has been observed that a thickness of 50 μm of adhesive on both surfaces the insulating layer is suitable. It is important that the insulating layer covers at least the edges of the metal sheet so that no metal part of

  the electrode is not exposed. Although the electrode represents

  FIGS. 1 and 2 comprise a substrate 12 of which

7 2459039

  the area is larger than that of the sheet metal-

  In the context of the invention, it is possible to use an insulating layer and a metal foil which reach the edge of the buffer forming the substrate. In this way, the entire surface of the electrode is used. The support material 12 preferably consists of cellular closed-cell foam material, for example polyurethane foam, polyvinyl chloride or the like. These materials resist the absorption of

  fluids. Alternatively, the substrate may consist of a fabric.

  A leaf of this kind is very flexible and easily marries the outline of the skin. The sheet 14 may be of any suitable material, electrically conductive, which may be formed into a thin, flexible sheet. An aluminum foil is advantageous, although it is also within the scope of the invention to use metallized plastic films, for example a film of

  metallised polyethylene terephthalate.

  The invention will be better understood with the aid of the examples which follow, but which can not in any way limit it.

EXAMPLE 1

  Temperature measurements by thermography were performed with 0.50C accuracy on human subjects to determine how the change in indifferent or passive electrode area affects skin temperature to the point where the electrode was fixed on her. A current of 1 ampere was sent back to

  indifferent electrodes prepared according to the invention.

  and fixed in the abdomen area of a subject for 1 minute. A 12.5 μm thick "Mylar" film was used to form the insulating material. These values of current intensity and duration represent a limit of the "worst possible case" of sending energy for

  electrosurgery operations and these values were determined

  analyzed by analysis of the maximum probabilities obtained

8. 2459039

  course of eighty surgical interventions. of the

  thermograms were taken by photograph about-

  seconds after power failure. This time interval is as short as possible taking into consideration the need to remove the electrodes from the subject before taking a thermogram. The results of these tests are shown in Figure 3. This shows that the temperature of the skin underwent the maximum rise with an electrode of 96.75 cm2, the temperature rise following an exponential curve as a function of the decrease in the dimensions of the electrode below this point. When

  the electrode has a surface area of 258 cm2 or a surface area

  higher, the temperature rise was about 0.51C,

  the temperature apparently no longer descending with the increase

  the area of the electrodes. The normal skin temperature is approximately 311C and a temperature of approximately 450C is required to cause tissue damage. Two indifferent direct coupling electrodes, previously gel-coated and commercially available, have also been tested to allow a comparison. Their surfaces were 77.5 and 155 cm2, respectively. The temperature rise measured when these electrodes were used was placed on the curve of the results obtained with the capacitive coupling electrode in order to make the comparison. As shown in FIG. 3, a capacitively coupled electrode of about 160 cm 2 would be required to produce an equivalent temperature rise to that of a 77.5 cm 2 direct coupled electrode and a capacitively coupled electrode. about 212.5 cm 2 to obtain a temperature rise equivalent to that of a direct coupling electrode with an area of 155 cm 2. Thus, a small elevation of the area of the capacitively coupled electrode allows it to utilize its ease of implementation and the improved safety it provides by maintaining substantially the same low rise in skin temperature as that obtained by the direct coupling electrodes that are available

9 2459039

  in the trade. In addition, as shown by the worst possible case example, capacitively coupled electrodes with an area of 193.5 cm2 or more cause

  elevation of skin temperature which is well above

  below the threshold at which damage could be caused to the tissues.

EXAMPLE 2

  The elevation of the skin temperature was measured in the same manner as in Example 1 for different thicknesses of the layer of insulating material of the capacitively coupled electrode according to the invention and

  whose skin contact area is 193.5 cm2.

  A current of 1 amp was also sent during

  60 seconds and the insulating material used was "Mylar".

  As shown in Figure 4, the thickness of the insulating layer

  lante has no importance on raising the temperature of the skin. An insulating material having a thickness of 12.5 pm gave results as good as twenty

  times thicker. So the factors that limit the thickness

  of the insulating material are the possibility of producing

  a thin film and the ability of this film to resist

  to the efforts that it undergoes during the manufacture of

  the electrode. Of course, the thinness of the iso-

  lante is also limited by the breakdown voltage at which an arc bursting through the insulating material risks

happen.

EXAMPLE 3

  The impedance (the ratio of the voltage applied to the current) of a circuit using a coupled electrode

  capacitive was measured using electrodes having different

  areas. The ideal case is that of an impedance of

  circuit is weak in order to avoid the risk of

  roving vagabond journeys. In other words, when the resistance to current flow is large, the current applied to the active electrode can seek another path to leave the body of a patient than the one passing through.

10. 2459039

  the return electrode. For example, when a patient is connected to an electrocardiogram

  small electrodes, part of the current applied to electricity

  Active electrosurgical trode could seek to leave the patient's body at the location of an electrocardiogram socket electrode. These electrodes having a weak

  area, the fabric could be injured at this location.

  as a result of the release of heat.

  As shown in Figure 5, the impedance of the 1C circuit decreases with increasing capacitance-coupled electrode area. For the tests, a current of 1 ampere was applied to the active electrode and the material

  insulation used in the passive electrode was a film

  "Mylar" capsule with a thickness of 12.5 μm. The impedance of previously gel-coupled, commercially available direct coupling electrodes has also been measured and measured.

  on the impedance curve to allow comparison.

  As in Example 1, these direct coupling electrodes had an area of 77.5 and 155 cm 2, respectively. Figure 6 shows the measurements of the currents along other paths for coupled electrodes.

  capacitive having different areas. A normal current

  1 amp was applied to the active electrode and an insulating layer 12.5 vm thick was used. Currents of less than 1 ampere were used for some tests when the magnitude of the currents of the other paths posed a problem of heating the small electrodes-taking electrocardiograms. All results have been plotted on the graph for normalized currents of 1 ampere. Small electrocardiograms electrodes were placed on the one hand near the location of use of the active electrode and on the other hand near the location where the return electrode was placed. capacitively coupled. As can be seen, the currents following different paths and measured near the corresponding electrocardiogram electrodes

  decreased with the increase in the area of electricity.

  capacitively coupled trode. This indicates that the larger the

  If the capacitance coupling electrode is large, the currents may follow different paths.

that of the patient.

EXAMPLE 4

  FIGS. 7 and 8 are graphs comparing the impedances and the different paths followed by the currents for a fixed-size capacitive coupling electrode, that is to say an area of 193.5 cm 2 as a function of the variation of the thickness of the insulating material. In this case also, the insulating material used was "Mylar" and a standardized current at 1 ampere as

  in example 3 was applied to the location of the elec-

  active trode. As shown in the graphs, the impedance as well as the different paths followed by the current increase with increasing thickness of the insulating material. The capacitive coupling electrode coated with adhesive according to the invention is safe and reliable when it is used. Because the adhesive covers the entire surface of the electrode, it ensures extremely fixed contact with the patient's skin and resists the risk of air gap formation that causes hot spots. Moreover, it is not necessary to deposit an adhesive net at the periphery, that is to say along the edges of the electrode; the entire area can be used as an electrode placed on a surface. As the examples show, electrodes having

  an area of 193.5 cm2 or more may be used

  with strong currents for periods of up to 1 minute without creating any dangerous rise in the temperature of the patient's skin. The heat rise is exponential with the decrease of the dimension of

  the electrode, an electrode of about 100 cm2 seems to represent

  the lower limit that can be used in practice to ensure safety. However, electrodes that may even have smaller dimensions may be useful in applications in which circulating current

is controlled.

12. 2459039

  On the graphs, the letters JD and PG indicate

  next to the curves are the initials of the people on

  which tests were carried out.

  It goes without saying that the invention has only been described by way of example and that it is capable of different

variants without departing from its scope.

13. 2459039

Claims (6)

  1. - Indifferent or passive electrode at   capacitive coupling, intended for use in electro-   surgery and connected to a generator, said electrode being supported by a substrate and being characterized in that   a layer of insulating material (16) covers said electrolyte   trode (14) and forms a surface for contacting the skin of a patient and a layer of a pressure sensitive adhesive (18) covers the entire surface of insulating material to be contacted with the skin.   2. - indifferent or passive electrode according to claim 1, characterized in that said electrode (14) reaches almost to the edges of the sheet forming said substrate (12).   3. - indifferent or passive electrode according to claim 1, characterized in that said sheet   forming the substrate (12) comprises an edge which extends   beyond that of the dielectric material (16) of said elec-   trode (14), this edge being covered with a pressure sensitive adhesive and allowing it to fix said electrode on the skin of a patient.   4. - Indifferent or passive electrode according to   claim 1, characterized in that said insulating material   lante (16) consists of a pressure-sensitive adhesive.   5. - Indifferent or passive electrode according to   claim 1, characterized in that said insulating material   lante is selected from the group consisting of polyethylene,   polyethylene terephthalate, polyvinyl chloride lidene and polysulfones.   6. - Indifferent or passive electrode according to   claim 1, characterized in that said insulating material   lante (16) has a thickness of between about 12.5 and about 250 pm.