CA2265849C - Capacitive reusable electrosurgical return electrode - Google Patents

Abstract

This invention is a reusable electrosurgical electrode pad for use with electrosurgery. In one embodiment, it includes a presentation or working surface area lying in the range of from about 11 square inches to about 1,500 square inches. In another, the working surface is at least as large as that of a projection of about half of the profile of the trunk of a patient. In yet another, it includes a working surface area at least as large as that of a projection of the profile of both the trunk and legs of a patient. It is adapted for disposition on the working surface of an operating table or dentist's chair immediately underlying a patient during electrosurgery. By presenting a very large surface area, the need for direct contact or contacts through conducting gels is eliminated. Through employment of washable surface areas, it is made readily cleanable and reusable. Through the inclusion of capacitive coupling and selection of impedance characteristics for the materials and geometries, it is made self-limiting as to current density and temperature rise so as to prevent patient trauma. An optional sleeve is provided for cooperative use with the electrode.

Description

l0l5253035lu\gagnggimg 135‘; $53; 5, E; Egg Q5133 QQAI, _13,.;i_T_trd~J ELI; green;Reference is herein made to co-pending United States Patent Application filed oneven date herewith and entitled "Resistive Reusable Electrosurgical Return Electrode."This invention relates to electrosurgery and more particularly to reusable return electrodesthat are adapted for providing effective and safe electrosurgical energy return withoutconducting or dielectric gels or polymers.BACKGROUNT3 QF THE INVENTIONAs is known to those skilled in the art, modern surgical techniques typicallyemploy radio frequency (RF) cautery to cut tissue and coagulate bleeding encountered inperforming surgical procedures. For historical perspective and details of such techniques,reference is made to United States Patent 4,936,842.As is known to those skilled in the medical arts, electrosurgery is widely used andotiers many advantages including that of the use of a single surgical tool for both cuttingand coagulation. Every electrosurgical generator system, to be fully used, must have anactive electrode which is applied by the surgeon to the patient at the surgical site toperform surgery and a return path from the patient back to the generator. The activeelectrode at the point of contact with the patient must be small in size to produce a highcurrent density in order to produce a surgical effect of cutting or coagulating tissue. Thereturn electrode, which carries the same current as the active electrode, must be largeenough in effective surface area at the point of communication with the patient such thata low density current flows from the patient to the return electrode» If a relative highcurrent density is produced at the return electrode, the temperature of the patient's skinand tissue will rise in this area and can result in an undesirable patient burn.In 1985, the Emergency Care Research Institute, a well known medical testingagency published the results of testing they had conducted on electrosurgical returnelectrode site burns, stating that the heating of body tissue to the threshold of necrosisoccurs when the current density exceeds lOC| milliamperes per square centimeter.The Association for the Advancement of Medical Instmmentation has publishedstandards that require that the maximum patient surface tissue temperature adjacent anelectrosurgical return electrode shall not rise more than 6 degrees Celsius under stated testconditions.Over the past twenty years, industry has developed products in response to themedical need for a safer rctum electrode in two major ways First, they went from a small,about 12x7 inches, flat stainless steel plate coated with a conductive gel, that was placedunder the patient's buttocks, thigh, shoulders, or any location where gravity can ensureCA 02265849 2002-09-30101520253035W0 98/181395CA 02265849 1999-03-09PCT/US97/ 184482adequate contact area to a flexible foam-backed electrode. These flexible electrodes whichare about the same size as the stainless steel plates, are coated with a conductive ordielectric polymer and have an adhesive border on them so they will remain attached tothe patient without the aide of gravity and are disposed of afier use. By the early 1980's,most hospitals in the United States had switched over to using this type of returnelectrode. These return electrodes are an improvement over the old steel plates andresulted in fewer patient return electrode burns but have resulted in additional surgicalcosts in the United States of several tens of million dollars each year. Even with thisimprovement, hospitals were still experiencing some patient burns caused by electrodesthat would accidentally fall off the patient during surgery.Subsequently, there was proposed a fiirther improvement, an Electrode ContactQuality Monitoring System that would monitor the contact area of the electrode that isin contact with the patient and turn oi? the electrosurgical generator whenever there wasinsufficient contact area. Such circuits are shown, for example, in United States patent4,231,372. This system has resulted in a much greater reduction in patient return electrodeburns but requires a special disposable electrode and an added circuit in the generatorwhich drove the cost per procedure even higher. Today, fifteen years after this system wasflrst introduced, fewer than 40 percent of all the surgical operations performed in theUnited States use this standard of safety because of its high costs.BRIEF ARY F THE NTI NThe present invention overcomes the problems of the prior art and provides areusable return electrode that eliminates patient burns without the need for expensivedisposable electrodes and monitoring circuits in specialized RF generators.Briefly, the improved return electrode according to the invention hereof includesan effective surface that is very much larger than any other return electrode that has beendisclosed or used in surgery previously. It is so large and so adapted for positioningrelative to the body of a patient that it eliminates any need for use of conductive ordielectric jells or polymers. Moreover, the exposed surface is of a material that is readilywashable and/or sterilizable so as to facilitate easy and rapid conditioning for repeatedreuse. It employs geometries and materials whose resistive and capacitive reactance(impedance) characteristics at typically used electrosurgical frequencies are such that itis self-limiting to limit current densities (and corresponding temperature rises) to safethresholds should the efiective area of the working surface of the electrode be reducedbelow otherwise desirable levels. Accordingly, the need for the foregoing expensivemonitoring circuits in specialized RF generators is eliminated.101520253035CA 02265849 1999-06-293B ._ ' I ‘ t.- Figure 1 is a simplified electrical schematic diagram illustrating typical impedanceseffectively included in the operative path of radio frequency current flow as presented toan electrosurgical generator during an operative procedure;Figure 2A is a top view of a wide-area distributed electrosurgical return electrode-‘ illustrating the principles of the invention.Figure 2B is an enlargement of a segment of the electrosurgical return electrodeof Figure 2A; IFigure 2C is a cross section taken along the section lines 2C—2C of Figure 2B andillustrating the effective circuit impedance represented by the segment of 2B;Figure 3 is a chart illustrating in graphical fonn the relationships between effectivesurface area of the return electrode and the effective radio frequency current densitydeveloped at the electrode; AFigure 4 is a perspective view showing an operating table with the electrosurgicalreturn electrode according to the invention disposed on the upper surface thereof; xFigure 5 is a front view illustrating a surgical chair with an electrosurgical returnelectrode according to the invention disposed on the surface of the seat thereof;Figure 6 is a top view of an electrosurgical return electrode according to theinvention;Figure 7 is a section taken along the lines 7-7 of Figure 6;Figure 8 is a section similar to that of Figure 7 but illustrating another multiplelayer embodiment according to the invention hereof;Figure 9 is a perspective view of a cover adapted for encasing either of theembodiments of Figures -6-8;Figure 10 is a view illustrating one of the embodiments of Figures 6-8 encasedwithin the cover of Figure 9; andFigure 1] is a cut-away view depicting one preferred embodiment with four layersof sandwiched materials.DE§$ Now turning to the drawing, and more particularly Figure 1 thereof, it will be seento depict a simplified electrical schematic diagram illustrating typical impedanceseffectively included in the operative path of radio frequency current flow as presented toan electrosurgical generator during an operative procedure. There, it will be seen areconventional radio frequency electrical power generator 10 to which there are connectedconventional electrical conductors 11 and 12 which respectively connect the generator tothe surgeon's implement represented by impedance 2, and an electrosurgical return10132025"30CA 02265849 1999-06-294electrode represented by impedance 23. Impedance z, is provided to represent theimpedance presented by the patient's tissue lying-between the ‘operation site and the returnelectrode.Although the diagram of Figure 1 is simplified and generally considers circuit. elements in terms of the principal resistances and reactances produced by the surgicalinstmment, patient's body and return electrode (so as to clearly and succinctly illustrateprinciples of the invention), it should be understood that in reality certain other parameterswould be encountered, parameters such as distributed inductance which, for purposes. ofclarity in illustration of the principles hereof are relatively small and not therefore notincluded in this description. In addition, and as set forth below, when an insulating sleeveis interposed between the electrode and the body of a patient, a significant additionalelement of capacitive reactance may be included in the impedance of z,.The initial embodiment hereof is that of an electrode operating in a combinedresistive and substantially capacitive mode. Accordingly, if the relatively small straycapacitive and inductive reactances are disregarded, the total effective impedance of thecircuit will be equal to the vector sum of the individual impedances z,, 2, and 23; and sinceessentially the same current will pass through all three, the voltage generated by R. F.generator 10 will be distributed across impedances 2,, z, and z, in proportion to theirrespective values. Moreover, the energy released in each of such principally resistivecomponents will be directly proportional to their values.Since it is desired that developed energy be concentrated in the region where thesurgeon's implement contacts the patient's tissue, it is desirable that the resistivecomponent of the impedance represented by 2, be substantial and that current passingtherethrough (and consequent energy release) be concentrated in a very small region. Thislatter is accomplished by making the region of contact with the patient at the operative sitevery small.It is known that, in contrast with the foregoing series circuit, components ofcombined resistance and capacitance, when connected in parallel, present a total effectiveimpedance that is given by the formula:Z1 Z2 Z3 Z3 Z4 Z5 Z6Thus, if 100 similar impedances each of 100 ohms were connected in parallel, the effectiveimpedance Z,, would equal one ohm. If half of such impedances were efiectively101520253035WO 98/18395CA 02265849 1999-03-09PCT/US97/ 184485disconnected, the remaining effective impedance would be two ohms, and if only one ofthe impedances were active in the circuit, the remaining effective impedance would be 100ohms. The significance of these considerations and their employment to render theelectrode hereof self regulating and fail-safe will be evident from the following descriptionof the elements illustrated in Figures 2A, 2B, 12C and 3.Now turning to Figure 2A, there will be seen a top view of a wide-area distributedelectrosurgical return electrode 20 illustrating the principles of the invention. At the righthand side of the figure there is shown an electrical terminal 22 to facilitate connection toa lead such as lead 12 of Figure 1.The surface 20A of return electrode 20 is preferably smooth homogeneous, andin accordance with this embodiment includes a thin dielectric layer 21a (Figure 2C). Forpurposes of this description, electrode 20 may be thought of as including a plurality ofuniformly-sized regions or segments as represented by regions 21, 21a, 21b 21c . . . . . .21n. Region/segment 21 is shown larger in Figure 2B in order to be similar in scale to theresistive impedance 23’ it represents. It thus will now be evident that each of the segmentsof electrode 20 corresponding to segments 21 . . . 21n inherently has the capability ofpresenting an impedance similar to that of impedance 23’. However, the number of suchsegments which are effectively active in parallel within the circuit is a function of thesurface area of the patient that overlies the electrode. Thus, in the case of a large supinepatient whose body is in effective registration with 50 percent of the upper surface of theelectrode, 50 percent of the segments corresponding to segments 21-2ln will beeffectively paralleled in the circuit to form an impedance represented by impedance 23 ofFigure 1; and accordingly if electrode 20 contains 100 segments of 100 ohms each, theeffective impedance operatively presented by the 50 percent of the electrode elementswould be 2 ohms. Since 2 ohms is very small compared with the impedance representedby elements 2, and 22, very little energy is dissipated at the region of contact between thepatient and the electrode, and due also to the relatively large effective working area of theelectrode, current density and temperature elevation are maintained below the dangerthresholds mentioned above.Now, if for any reason, the effective contact area between the patient andelectrode were to be reduced to the surface of only one of the segments 2l—2ln, then theeffective impedance (combined capacitive reactance and resistance in the example underconsideration) would increase to 100 ohms; and at some point of reduction in contactarea, the effective impedance would rise to a level (relative to the impedance presentedat the site of the surgeon's instrument) so as to prevent effective use of the instrument bythe surgeon, thus signalling the surgeon that the patient should be repositioned so as tol0I52030356present a greater surfacéarea in contact with return electrode.’At\‘th'e same time, the totalcircuit impedance would be increased so that the total current that would flow if thesurgeon attempted to employ his instrument without repositioning the patient would bereduced to a value below that which would cause undesired trauma to the patient.Accordingly, there is provided a self-limiting feature that enhances safety in use withoutthe need for the aforementioned separate circuit monitoring and control circuits.Figure 2C is a cross section taken along the section lines 2C—2C of Figure 2B andillustrating the eflective circuit impedance 23’ represented by the segment 2] of 213, There,in Figure 2C are seen small segment 21 with its upper patient-contacting surface 24represented electrically by terminal 23 and its lower surface 25 represented by electricalTerminal 22a. For the purpose ofthis description (and in order to present the principlesunderlying this embodiment clearly), the impedance 7.3’ may be thought of as existingbetweenTermina]s 23 and 22a. Of course, it will be evident to those skilled in the art thatin an embodiment in which a thin but highly conductive layer is included along the lowersurface of electrode 20 as described below, each of the impedances represented by theremaining segments are connected at their lower extremities in parallel to terminal 22,whereas if such highly conductive layer is absent, then in addition to the impedancerepresented by the material lying between the upper and lower regions of each segment,there will be an additional impedance (not shown) that is represented by the material‘ through which current would have to pass transversely or laterally through the electrodein order to get to terminal 22.lt should now be evident that if lateral impedance is minimized by provision of theaforementioned thin conducting layer, or if the effective conductivity at the lower part ofthe material of region 21 is otherwise increased, the effective impedance presented by thereturn electrode will be inversely proportional to the effective upper surface of theelectrode that is in contact with a patient.Figure 3 is a chart generally illustrating in graphical form the relationships betweeneffective surface area of the return electrode and the effective radio frequency currentdensities developed at the electrode. However, before proceeding to a consideration ofsuch chart, it should be noted that the chart is simplified so as to illustrate the principlesunderlying the invention and does not represent actual data that may vary substantially.In Figure 3 there are seen a plot of R. F. Density vs Electrode Effective Surface Area, thelatter (as should now be evident to those skilled in the. art’) being that part ofthc surfaceof the return electrode that makes effective electrical interaction with the body of apatient. As would be expected from the foregoing discussion, when the effective area islarge, the voltage at the surgeon's implement is high (dashed graph line 30) and theCA 02265849 2002-09-30101520253035W0. 98/ 18395CA 02265849 1999-03-09PCT/US97/184487corresponding current density across the return electrode is very low (solid graph line 31).This is, of course the condition desired for conducting surgery. However, as the effectivesurface area decreases, the current density across the return electrode increases and thereis a corresponding decrease of the current at the surgeon's instrument until if the effectivesurface area declines to some predetermined point, there will remain insufficient currentat the surgical instrument to conduct surgery. The parameters selected for the materialsand electrode dimensions are chosen so that current density and corresponding tissuetemperature elevation adjacent the return electrode do not exceed the limits mentioned inthe introduction hereof. It will now be seen that by a proper selection of such parameters,the return electrode is made self-limiting, thereby obviating the need for the additionalmonitoring circuits to which reference is made above.In this description of the principles underlying this invention, the foregoing aredescribed in terms of impedances whose principal components are both resistances andcapacitive reactances. Nevertheless, as set forth in the above-identified co-pendingapplication, the principles of the invention are also applicable to embodiments in whichthe impedances are principally resistive.The invention hereof is now further described in connection with applications inwhich an effective dielectric layer is represented by a physical dielectric layer on the uppersurface of the electrode, by the material of the surgical gown of the patient, by thematerial of a sleeve fitted on the electrode, or a combination thereof.Now turning to Figure 4, it will seen to illustrate in perspective an operating table40 with an electrosurgical return electrode 41 according to the invention disposed on theupper surface thereof, an edge of which is identified by the numerals 42. The operatingtable is shown to have conventional legs 44a--44d which may be fitted with wheels orrollers as shown.Although in Figure 4, the entire upper surface of the table is shown as beingcovered with return electrode 41, it should be understood that entire coverage is by nomeans required in order to practice the principles of the invention. Thus when used withconventional electrosurgical generators, the return electrode needs only to present aneffective working surface area which is sufficient to provide adequate resistive/capacitivecoupling at the typically employed RF frequencies so as not to interfere with the surgeon'sability to perform surgery while at the same time avoiding undesired tissue damage. It hasbeen found that at conventional electrosurgical generator frequencies, this has necessitatedonly an efiective working surface of no more than the projected outline of one-half of thetorso for an adult patient lying on an operating; table or the buttocks of a patient sittingin a chair such as is illustrated in Figure 5. However, with some materials and in some1015203035WO 98/18395CA 02265849 1999-03-09PCT/US97/ 184488geometrical configurations, the principles hereof may be successfully employed when theeffective working surface area of the return electrode is as small as eleven square inches.Moreover, although the return electrodes shown in Figures 6-8 are depicted as beingrectangular in shape, it will be evident that they could be oval or contoured as, forexample, to follow the silhouette of the torso or other principal part of the body of apatient. As will be evident from the foregoing, it is important that the electrode be ofsufficient size so that when it is in use: (1) the return current density on the surface of thepatient is sufficiently low; (2) the electrical impedance between it and the patient issufficiently low so that insuflicient electrical energy is concentrated to heat the skin of thepatient at any location in the electrical return path by more than six (6) degrees Celsius;and (3) the characteristics of the materials and geometries are such that if the effectivearea of the electrode is reduced below a selected threshold level, there will be insufficientenergy dissipated at the surgeon's implement for him to continue effectively using theimplement in its electrosurgical mode.As is known to those skilled in the art, in an alternating current circuit (e. g., suchas those used in electrosurgery) the capacitive reactance of an impedance is a functionboth of capacitance and the frequency of the alternating current electrical signal presentedto the reactance. Thus, the formula for capacitive reactance (in ohms) is:lXc=——j—21'CfCwhere Xc is capacitive reactance in ohms, is 3.14159, f is frequency in hertz, and C iscapacitance in farads.The formula for capacitance in a parallel plate capacitor is :0.224 KA (n-1)dC .where C is capacitance in picofarads, K is the dielectric constant of the material lyingbetween the effective plates of the capacitor, A is the area of the smallest one of theeffective plates of the capacitor in square inches, d is separation of the surfaces of theeffective plates in inches, and n equals the number of effective plates. Thus, it will be seenthat to meet the foregoing maximum permissible temperature rise criteria in anembodiment in which electrode capacitance is substantial, different minimum sizes ofelectrodes may be required depending upon the frequency of the electrical generatorsource, the separation of the body of the patient from the electrode, and the material lyingbetween the effective conductive region of the electrode and the adjacent body surface.101520253035W0 98/ 18395CA 02265849 1999-03-09PCT/US97/184489Accordingly, although the principles of the invention are applicable to a wide range offrequencies of electrosurgical energy, the considerations set forth herein for minimumsizes of return pads specifically contemplate frequencies typically employed inconventional electrosurgical energy generators.Those skilled in the art know that, with the currently used disposable returnelectrodes, reducing the effective size of the electrode to three square inches will notreduce the RF current flow to a level where it will impede the surgeon's ability to performsurgery nor concentrate current to a level to cause patient trauma. However, to providefor some spacing of the electrode from the patient's body, a corresponding returnelectrode according to the invention hereof would need an effective area of eighteensquare inches with a relatively small separation from the skin of the patient such as thatprovided by a surgical gown or no interposing gown at all. Such an effective area is easyto obtain if the patient is positioned on an electrode that is the size of their upper torso orlarger.The characteristics of the desired dielectric are sufficiently comparable to that ofselected rubbers, plastics and other related materials that the latter may be satisfactorilyemployed as materials for the return electrode. As mentioned above, with such a returnelectrode, if the patient is positioned such that not enough of the return electrode is inclose proximity to the patient to result in as low impedance as needed, the results wouldbe that the current flow from the electrosurgical generator would be reduced to a levelmaking it difficult for the surgeon to perform surgery. Thus, in the present embodiment,notwithstanding interposition of some additional capacitance represented by a surgicalgown, the features described above will continue to occur.As mentioned above, Figure 5 is a front view illustrating a surgical chair 50 withan electrosurgical return electrode 51 according to the invention disposed on the uppersurface of the seat thereof. Accordingly, when a patient is sitting in the chair, the buttocksand upper part of the thighs overlie and are in sufficiently close proximity to the returnelectrode so that capacitive coupling therebetween presents an impedance meeting theforegoing criteria; namely, that the electrical impedance between it and the patient issufficiently low to allow the surgeon to perform the procedure while providing thatcurrent density is sufiiciently low and that insufficient electrical energy is developed acrossthe return impedance to heat the skin of the patient at any location in the electrical returnpath by more than six (6) degrees Celsius.Figure 6 is atop view of another electrosurgical return electrode according to theinvention. It will be observed that the upper exposed, or working, surface of the electrodeagain is expansive so as to meet the foregoing criteria for low impedance. Although it is10152025303510I\/snot necessary that the eiaztrode cover the entire surface of an operating table or the entireseat surface of a dental or other patient chair, it has been found advantageous in someinstances to provide a greater surface area than that ofthe projected area of the buttocksor torso of a patient so that if a patient moves position during the course of a procedure,a sufficient portion of the patient outline will remain in registration with the electrodesurface so that the foregoing impedance will remain less than the above-described level.At this juncture, it may be helpful to emphasize characteristics ofthe improvedelectrode according to the invention hereof, that are deemed particularly relevant to anunderstanding of the inventive character thereof. First, as mentioned above, the electrodedoes not need to be in contact with a patient either directly or through interveningconductive or nonconductive gel. In addition, due to its expansive size, there is no needfor tailoring the electrode to fit physical contours ofa patient. In this connection, it hasbeen found that although with selected materials and geometries, self-correcting, selflimiting principles hereof could be achieved in an electrode as small as 7 square inches inworking surface area, the preferable range of exposed upper working surface area of theelectrode lies in the range offrom about 1 l to 1500 square inches. However, by makingthe electrode several times larger (typically, at least an order of magnitude larger) inworking surface area than previous proposals, the need for physical attachment directlyor through gels is eliminated.The electrode according to the invention hereof as illustrated in Figure 6, mayinclude conductive plastic, rubber or other flexible material. Silicon or butyl rubber havebeen found to be particularly attractive materials as they are flexible as well as readilywashable and sterilizable. The main body of the return electrode may be made ofinherently relatively high resistance flexible material altered to provide the requisiteconductivity. A preferred example of the latter is that of silicon rubber’ material in whichthere are impregnated conductive fibers suclfas those of carbon or in which there havebeen distributed quantities of other conductive substances such as carbon black, quantitiesof gold, silver, nickel, copper, steel, iron, stainless steel, brass, aluminum, or otherconductors.Further reference to Figure 6 reveals the presence of a conventional electricalconnector 54 attached to the electrode 41 to provide a conventional electrical return tothe electrosurgical radio frequency energy source (not shown).As mentioned above, Figure 7 is a section taken along the lines 7-7 of Figure 6.There is seen an electrode similar to electrode 20 of Figures 2A—2C except thatthe electrode of Figure 7 includes a thin highly conductive lower stratum 46c to facilitate .conduction of current outwardly to terminal 54. In one preferred form, the thickness ofCA 02265849 2002-09-30l015203035llthe electrode lies in a~range from about l/32nd to l/4th of an inch, which, with theaforementioned resistance of the main body of material and the capacitance of upperdielectric layer 47a, provides the required impedance together with desired physicalflexibility for ease of use and handling.Figure 8 is a section similar to that of Figure 7 but illustrating an embodiment witha greater number of layers according to the invention hereof There, in Figure 8 is showna layer 4621 (preferably similar to layer 46 of Figure 7) with the overlying insulatingdielectric layer 4721 being sufliciently thick to ensure withstanding the level of radiofrequency voltage thereacross and preferably comprised of material such as plastic, silicon «rubber or Teflon. *lt should be understood that in addition to a construction similar to thatofthe electrode ofFigures 6-7, a highly conductive layer 47c ofFigure 8 could comprisea sheet or screen of gold, brass, aluminum, copper, silver, nickel, steel, stainless steel,conductive carbon or the like. Thus, according to the construction of Figure 8, a dielectriclayer 47a includes an upper working surface 47b for presentation either directly orthrough a surgical gown or the like to a major portion, e.g., at least half of the trunkportion or the buttocks and upper thigh regions of a patient. Further reference to Figure8 reveals another dielectric layer 47d covering the lower surfaces oflayer 46a.Figure 9 is a perspective view ofa sleeve 70 adapted for encasing any one of theembodiments of Figures 6-8. Thus, provision is optionally made for encasing theforegoing return pad-shaped electrodes within protective envelopes in situations in whichit is desired to eliminate the need for cleaning the electrode itself by protecting it fromcontamination through the use of a sleeve of impervious material from which theelectrode, alter use, can merely be withdrawn and the sleeve discarded. As will be evidentto those skilled in the art, such a sleeve may preferably be made of any of a variety ofknown materials such as vinyl plastics, polyester or polyethylene.Figure 10 is a view illustrating one of the embodiments of Figures 6-8 encasedwithin the sleeve ofFigure 9. There, it will be seen is outer surface 70a of sleeve 70; andshown encased within sleeve 70 for illustrative purposes is electrode 41 ofFigure 6.As mentioned above, Figure 11 is a cut-away view depicting an embodiment withfour layers of sandwiched materials. At the top of the large area surface 60 there is a thinvinyl dielectric layer 61 which overlies a highly conductive metallic foil layer 62 that, intum overlies a thin paper layer 63 which overlies a second thin vinyl layer 64. Except forthe paper layer 63, the layers 61, 62 and 64 correspond to layers previously describedherein, the paper layer being optional and provided to decrease coupling with metallictables on which the electrode may be employed. Electrical connection 65 is provided formaking connection to an electrosurgical energy source return conductor 66.;" 'l‘l{.»'\l)l{—M/\Rl{CA 02265849 2002-09-301012\it will now be‘evident that there has been described /herein an improvedelectrosurgical return electrode characterized by being generally pad-shaped andevidencing the features of being self-limiting while being reusable, readily cleanable andobviating the necessity for use of conducting gels or supplementary circuit monitoringequipment.Although the invention hereof has been described by way of preferredembodiments, it will be evident that adaptations and modifications may be employedwithout departing from the spirit and scope thereof. ;The terms and expressions employed herein have been used as terms of descriptionand not of limitation; and thus, there is no intent of excluding equivalents, but on thecontrary it is intended to cover any and all equivalents that may be employed withoutdeparting from the spirit and scope of the invention.CA 02265849 2002-09-30

Claims (25)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS;

1. A reusable electrosurgical return electrode comprising:
(a) a first thin layer of electrically-conductive material, said first thin layer having a major surface and having connection means for making electrical connection to said first layer;

(b) a second thin layer of electrically insulating dielectric material contacting and overlying essentially all of said major surface of said first thin layer thereby to form a sandwich of said first and said second thin layers, said second thin layer having an exterior upper major surface including an exterior working surface adapted for disposition immediately adjacent at least a major part of the trunk region of a patient positioned for electrosurgery, wherein said area of said exterior working surface is substantially equal to or greater than the projected area of the entire body of said patient.

2. A reusable electrosurgical return electrode according to claim 1 wherein said area of said exterior working surface is at least substantially equal to the projected area of the entire body of said patient.

3. A reusable electrosurgical return electrode according to claim 1 wherein said area of said exterior working surface is sufficient to substantially cover an operating table adapted for supporting said patient when in a horizontal position.

4. In combination, a reusable electrosurgical return electrode comprising:
(a) a first thin layer of electrically-conductive material, said first thin layer having a major surface and having connection means for making electrical connection to said first layer;

(b) a second thin layer of electrically insulating dielectric material contacting and overlying essentially all of said major surface of said first thin layer thereby to form a sandwich of said first and said second thin layers, said second thin layer having an exterior upper major surface including an exterior working surface adapted for disposition immediately adjacent at least a major part of the trunk region of a patient positioned for electrosurgery, wherein said area of said exterior working surface is at least substantially equal to the projected area of the entire body of said patient and an insulating sleeve substantially covering said exterior upper major surface.

5. The combination of a reusable electrosurgical return electrode and insulating sleeve according to claim 4 in further combination with said operating table.

6. In combination, a reusable electrosurgical return electrode comprising:

(a) a first thin layer of electrically-conductive material, said first thin layer having a major surface and having connection means for making electrical connection to said first layer;

(b) a second thin layer of electrically insulating dielectric material contacting and overlying essentially all of said major surface of said first thin layer thereby to form a sandwich of said first and said second thin layers, said second thin layer having an exterior upper major surface including an exterior working surface adapted for disposition immediately adjacent at least a major part of the trunk region of a patient positioned for electrosurgery, said exterior working surface having at least 11 square inches and an insulating sleeve substantially covering said exterior upper major surface.

7. A reusable electrosurgical return electrode comprising a sheet of material having:

(a) a principal layer of predetermined limited electrical conductivity, said principal layer having an upper major surface;
(b) a layer of dielectric material contacting and overlying said principal layer;
(c) connecting means for making electrical connection to said sheet;
(d) a working surface on said major surface adapted for disposition immediately adjacent the trunk region of a patient positioned for electrosurgery, said working surface having an area equal to or greater than one-half the projected area of said trunk region of said patient; and (e) self-limiting means including said predetermined limited electrical conductivity and capacitive reactance of said dielectric layer for limiting density of electrosurgical current flowing through said electrode to less than 100 milliamperes per square inch of said working surface area.

8. A reusable electrosurgical return electrode according to claim 7 wherein capacitive impedance exhibited by said dielectric layer lies in a range from one to 250 .OMEGA./in2 of said working surface.

9. A reusable electrosurgical return electrode according to claim 7 wherein effective resistivity presented by said sheet of predetermined limited electrical conductivity lies in a range of from one to about 250 .OMEGA./in2 of said working surface area.

10. A reusable electrosurgical return electrode according to claim 7 wherein said self-limiting means includes means for limiting temperature rise of patient tissue in registration with said electrode to 6 degrees Celsius when current is flowing through said electrode during a surgical procedure.

11. A reusable electrosurgical return electrode according to claim 7 wherein said capacitive impedance of said dielectric layer lies in a range of from about one ohm to about 250 .OMEGA./in2 of said working surface area and wherein said self-limiting means includes means for limiting temperature rise of patient tissue in registration with said electrode to 6 degrees Celsius when current is flowing through said electrode during a surgical procedure.

12. In combination, a reusable electrosurgical return electrode according to claim 7 and means including an electrosurgical instrument in operating deployment, wherein said self-limiting means includes means for noticeably reducing effectiveness of said electrosurgical instrument when said density of said electrosurgical current flowing through said electrode rises to approach a predetermined level.

13. A reusable electrosurgical return electrode comprising:
(a) a sheet of material having (i) a first layer of predetermined limited electrical conductivity;
(ii) a second layer of dielectric material having a predetermined capacitive reactance, said second layer contacting and overlying said first layer; and (b) connecting means for making electrical connection to said sheet, wherein said predetermined limited electrical conductivity and said predetermined capacitive reactance automatically and continuously limit the density of electrosurgical current flowing through said electrode to less than 100 milliamperes per square inch.

14. A reusable electrosurgical return electrode comprising:
(a) a sheet of material having a first layer of predetermined limited electrical conductivity and a second layer of dielectric material having a predetermined capacitive reactance, said second layer contacting and overlying said first layer;
(b) connection means for making electrical connection to said sheet;
and (c) self-limiting means, including said predetermined limited electrical conductivity and said predetermined capacitive reactance, for limiting the density of electrosurgical current flowing through said electrode to less than 100 milliamperes per square inch of said electrode.

15. A reusable electrosurgical return electrode comprising:
(a) a sheet of material having (i) a first layer of predetermined limited electrical conductivity;
(ii) a second layer of dielectric material having a predetermined capacitive reactance, said second layer contacting and overlying said first layer and having a working surface adapted for disposition adjacent the tissue of a patient positioned thereon for electrosurgery; and (b) connecting means for making electrical connection to said sheet, wherein said predetermined limited electrical conductivity and said predetermined capacitive reactance continuously and automatically regulate the electrosurgical current flowing through said electrode as a function of the area of contact between said electrode and said patient's tissue so as to limit the density of said electrosurgical current to less than 100 milliamperes per square inch.

16. A reusable electrosurgical return electrode comprising:
(a) a sheet of material having a first layer of predetermined limited electrical conductivity and a second layer of dielectric material having a predetermined capacitive reactance, said second layer contacting and overlying said first layer and having a working surface adapted for disposition adjacent the tissue of a patient positioned thereon for electrosurgery;
(b) connection means for making electrical connection to said sheet;
and (c) self-limiting means, including said predetermined limited electrical conductivity and said predetermined capacitive reactance, for continuously and automatically regulating the electrosurgical current flowing through said electrode as a function of the area of contact between said electrode and said patient's tissue so as to limit the density of said electrosurgical current to less than 100 milliamperes per square inch.

17. The reusable electrosurgical return electrode of claim 13, 14, 15 or 16, wherein the effective electrical conductivity of the sheet is within a range from about 1 to about 1/250th ohm per square inch.

18. The reusable electrosurgical return electrode of claim 13, 14, 15 or 16, wherein said sheet has a surface area equal to or greater than 11 square inches.

19. The reusable electrosurgical return electrode of claim 13, 14, 15 or 16 wherein said sheet has a surface area within a range from 11 to 1,500 square inches.

20. The reusable electrosurgical return electrode of claim 13, 14, 15 or 16 further comprising an insulating sleeve substantially enclosing said sheet.

21. In combination, a reusable electrosurgical return electrode according to claim 14 or 16 and means including an electrosurgical instrument in operating deployment, wherein said self-limiting means includes means for noticeably reducing the effectiveness of said electrosurgical instrument when said density of said electrosurgical current rises to approach a predetermined level.

22. The reusable electrosurgical return electrode of claim 14 or 16, wherein said self limiting means further comprises means for limiting temperature rise of patient tissue in registration with said electrodesurgical return electrode to 6 degrees Celsius when current is flowing through said electrosurgical return electrode during a surgical procedure.

23. The reusable electrosurgical return electrode of claim 15 or 16, wherein said working surface is sterilizable.

24. The reusable electrosurgical return electrode of claim 15 or 16, wherein said working surface is washable.

25. The reusable electrosurgical return electrode of claim 13, 14, 15 or 16 wherein said first layer is comprised of a normally insulating material impregnated with electrically conducting material to render said first layer at least partially conductive.