CA2627972A1

CA2627972A1 - System and method for providing even heat distribution and cooling return pads

Info

Publication number: CA2627972A1
Application number: CA002627972A
Authority: CA
Inventors: James E. Dunning
Original assignee: Tyco Healthcare Group LP
Current assignee: Covidien LP
Priority date: 2007-04-03
Filing date: 2008-04-01
Publication date: 2008-10-03
Also published as: US20080249524A1; JP2008253777A; EP1977709A1; AU2008201502A1

Abstract

The present disclosure relates to a return pad for use with an electrosurgical system and includes a contact layer configured to engage patient skin, a conductive layer disposed on the contact layer, and a heating layer operatively associated with at least one of the contact layer and the conductive layer. The heating layer is configured to heat the return pad.

Description

SYSTEM AND METHOD FOR PROVIDING
EVEN HEAT DISTRIBUTION AND
COOLING RETURN PADS
BACKGROUND

Technical Field [00011 The present disclosure is directed to electrosurgical apparatus, methods and systenis, and, in particular, to an electrosurgical return pad that provides even heat and current distribution and cooling.

Backerouad of Related Art

[0002] During monopolar electrosurgery, a source or active electrode delivers energy, such as radio frequency energy, from an electrosurgical generator to the patient and a return pad carries the current back to the electrosurgical generator.
The source electrode is typically placed at the surgical site and high density current flows from the source electrode to create the desired surgical effect of cutting and/or coagulating tissue.
In tissue ablation, another form of electrosurgery, the source electrode or electrodes are typically placed in or adjacent the target tissue and high density current flows through the target tissue thereby destraying the target tissue. The patient return pad is placed at a distance from the source electrode and may be in the form of a pad adhesively adhered to the patient.

[00031 The return pad typically has a large patient contact surface area to minimize heating at that return pad site. The larger the contact area between the return I

pad and patient skin, the lower the current density and the lower the intensity of the heat.
The size of return pads is based on assumptions of the maximum current seen in surgery and the duty cycle (e.g., the percentage of time the generator is on) during the procedure.
The first types of return pads were in the form of large metal plates covered with conductive jelly. Later, adhesive electrodes were developed with a single metal foil covered with contact layer formed of conductive jelly, conductive adhesive or conductive hydrogel.

[00041 One issue with these adhesive electrodes was that current flow from the active electrode concentrates at the leading edge, the edge of the return pad closest to the active electrode, causing a heating imbalance across the return pad. This phenomenon, known as "Leading Edge Effect" can cause tissue change or injury if the skin under the leading edge portion of the return pad is heated beyond the point where circulation of blood can cool the skin.

SUMMARY
[0005] The present disclosure relates to a return pad for use with an electrosurgical system and includes a contact layer configured to engage patient skin, a conductive layer disposed on the contact layer, and a heating layer operatively associated with at least one of the contact layer and the conductive layer. The heating layer is configured to heat the return pad.

[00061 The heating layer may include at least one electric heating element configured to receive power from an external power supply. And the extemal power supply may limit the energy supplied to the at least one electric heating element to prevent the return pad from exceeding a target temperature.

[0007] The return pad may further include a temperature sensor operable to sense the temperattue of the return pad. In this embodiment, the extemal power supply may be operable to control the temperature of the return pad to at least one of reaching the target temperature and maintaining the target temperature.

1000$1 In another embodiment, the return pad may include at least one energy regulating device that prevents the return pad from exceeding a target temperature. The energy regulating device may be selected from a group consisting of a current limiting fuse, a thermal cut-off device, and a timer.

100091 In yet another embodiment, the heating layer may include an exothermic pack, and the energy generated by the exothermic pack may be operable to

3 heat the return pad to about a target temperature or to limit heating the return pad to a temperature above the target temperature.

[00010] In another embodiment, a return pad for use with an electrosurgical system includes a conductive layer, and a contact layer having a first side configured to engage patient skin and a second side disposed on the conductive layer. The contact layer includes at least one electric heating element at least partially disposed in the contact layer, and the electric heating element may be configured to receive power from an extemal power supply. The electric heating element may be configured to heat the contact layer to about a target temperature prior to engaging the contact layer to patient skin.

[000111 The exteraal power supply may be operable to limit the energy supplied to the at least one electric heating element to prevent the contact layer from exceeding the target temperature.

[00012] The return pad may further include a temperature sensor operable to sense the temperature of the return pad, or at least one energy regulating device operable to prevent the contact layer from exceeding the target temperature. The energy regulating device may be selected from a group consisting of a current limiting fuse, a thermal cut-off device, and a timer.

4 BRIEF DESCRIPTION OF THE DRAWINGS

[00013] The above and other aspects and features of the present disclosure will become more apparent in light of the following detailed description when taken in conjunction with the accompanying drawings in which:

[00014] FIG. 1 A is a schematic illustration of a monopolar electrosurgical system with a return pad;

[00015] FIG. 1 B is a detail of the leading edge of the return pad of FIG. 1;

[00016] FIG. 2A is a cross-sectional view of one envisioned construction of a return pad with an intermediate layer of the present disclosure;

[00017] FIG. 2B is a cross-sectional detail of the leading edge of the return pad of FIG. 2;

[00018] FIG. 3A is a cross-sectional view of yet another embodiment of a return pad having an intermediate layer disposed between a conductive layer and a first contact layer, [00019] FIG. 3B is a cross-sectional detail of the leading edge of the return pad of FIG. 3;

[00020] FIG. 3C is a top view of yet another embodiment of the return pad of FIGS. 3A-3B with an insulating barrier between the conductive gel portions;

[00021] FIG. 4A is a cross-sectional view of yet another embodiment of a return pad with an intermediate layer;

[000221 FIG. 4B is a cross sectional detail of the leading edge of the return pad of FIG. 4;

(00023] FIG. 4C is a top view of yet another embodiment of the return pad of FIGS. 4A-4B with an insulating barrier between the conductive gel portions;

[00024] FIG. 5 is a cross-sectional view of a return pad with a plurality of contact layers;

[00025] FIG. 6A is a cross sectional view of a return pad with a passive cooling layer;

[00026] FIG. 6B-6E illustrate various embodiments of passive cooling layers;
1000271 FIG. 7 is a top view of a return pad with an active cooling system;

[000281 FIG. 8 is a top view of the return pad of FIG. 7 with an even heat distribution layer;

[00029] FIG. 9 is a cross-sectional view of yet another embodiment of an active cooling system with an intermediate layer;

[00030] FIG. IOA is a cross-sectional view of yet another embodiment of a return pad with a heating layer;

[000311 FIG. l OB is a top view of the return pad of FIG. l0A wherein the heating layer utilizes an electric heater, and [00032] FIG. IOC is a cross-sectional view of a return pad with the heating layer disposed in at least a portion of the contact layer.

DETAILED DESCRIPTION

[00033] Embodiments of the presently-disclosed electrosurgical return electrode (return pad) and method of using the same are described below with reference to the accompanying drawing figures wherein like reference numerals identify similar or identical elements. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the disclosure in unnecessary detail. In addition, terms such as "above", "below", "forward", "rearward", etc. refer to the orientation of the figures or the direction of components and are simply used for convenience of description.

[00034] Heat Distribulion [00035] Referring initially to FIG. IA, a schematic illustration of a monopolar electrosurgical system 100 is shown. The electrosurgical system 100 generally includes a return pad 200, an electrosurgical generator l 10, a surgical instrument 116 (e.g., an active electrode) and a return electrode monitor (REM) 112. In FIG. 1 A and in the figures hereinbelow, return pad 200 is illustrated in contact with patient tissue "T".
Generally, electrosurgical energy is supplied to the active electrode 116 by the generator 110 through a supply cable 114 to treat tissue (e.g., cut, coagulate, blend, etc.). The return pad 200 acts as a return path for energy delivered by the active electrode 116 to patient tissue "T". Energy returns back to the electrosurgical generator 110 via a return cable 118.

1000361 While FIGS. l A-9 depict cross-sections of return pads 200, 300, 400, 500, 600, 600a-d, 700 and 800, it is within the scope of the disclosure for the return pads to have any suitable regular or irregular shape.

[000371 In the embodiments illustrated in FIGS. IA and 1B, return pad 200 is formed of a conductive layer 210 engaged on the top with an insulating layer 212 and on the bottom with a contact layer 215. Conductive layer 210 connects to generator 110 by return cable 118 in any suitable manner.

1000381 Contact layer 215 is formed of a gel or adhesive configured to couple to patient tissue "T" and can be made from, but is not limited to, a polyhesive adhesive, conductive hydrogel, a Z-axis adhesive or a water-insoluble, hydrophilic, pressure-sensitive adhesive. The portion of the contact layer 215 in contact with a patient tissue "T' is a patient-contacting surface 216 that is configured to ensure an optimal contact area between the return pad 200 and the patient tissue "T". In addition, contact layer 215 provides ionic conductive contact with the skin to transfer energy out of the body.

[00039] A leading edge 205 of the return pad 200 is that portion of the return pad 200 positioned closest to the active electrode 116. Leading edge 205 is defined in this disclosure not as a single point but as a generai portion of the return pad 200 positioned closest to the active electrode 116.

[00040J In use, the current applied by the active electrode 116 travels through various tissue paths between the active electrode 116 and the return pad 200.
The amount of current supplied by the active electrode 116 is typically equal to the amount of current received by the return pad 200. The only difference between the active electrode 116 and the return pad 200 is the amount of area in which the current is conducted.
Concentration of electrons at the active electrode 116 is high due to the small surface area of the active electrode 116, which results in high current density and generation of heat, while the large surface area of the return pad 200 disperses the same current over the large contacting surface 216 resulting in a low current density and little production of heat.
1000411 Electric charge passing between the active electrode 116 and the return pad 200 will travel along various paths in patient tissue "T" and will seek the path with the lowest impedance. With reference to FIGS. 1 A-4, three tissue paths (TP
1), (TP2) and (TP3) are provided for illustrating tissue paths with varying impedances.
However, any number of suitable paths may be utilized for conducting current through tissue "T'.
[000421 Tissue path one (TP1) is a path in patient tissue "T" between the active electrode 116 and the leading edge 205 of return pad 200. Tissue path two (TP2) and tissue path three (TP3) are paths in patient tissue "T" between the active electrode 116 and a portion of the return pad 200 away from the leading edge 205 of the return pad 200.
1000431 The total impedance of a given pathway between the active electrode and the return cable 118, through the return pad 200, is detenmined by combining the impedance of the tissue pathway and the impedance of the various layers of the return pad 200. As illustrated in FIG. 1 B, the impedance of the first path equals the sum of the impedance of the first tissue path (TPI), the impedance of the first adhesive path (AP 1) through the contact layer 215 and the impedance of the first conductive path (CP 1) through the conductive layer 220. Similarly, the impedance of the second path equals the sum of the impedance of the second tissue path (TP2), the impedance of the second adhesive path (AP2) and the impedance of the second conductive path (CP2).
Finally, impedance of the third path equals the sum of the impedance of the third tissue path (TP3), the impedance of the third adhesive path (AP3) and the impedance of the third conductive path (CP3).

[000441 In comparing the impedance of the various portions of the three illustrative current pathways, the impedance of adhesive paths (AP1), (AP2) and (AP3) and the impedance of conductive paths (CPI), (CP2) and (CP3) are substantially the same regardless of the tissue path selected. In addition, the impedance of adhesive path (AP1), (AP2) and AP3 and the impedance of a conductive path (CPI), (CP2) and (CP3) are generally small in comparison to the impedance of a tissue path (TPI), (TP3) and (TP3) and are therefore negligible with respect to the impedance of each respective tissue path (TP1), (TP2) and (TP3). Therefore, the current density at any point on the contacting surface 216 is generally dependant on the impedance of the tissue path.

1000451 As illustrated by perpendicular "P" drawn from first tissue path (TP
1) in FIG. 1B, the lengths of the second and third tissue paths (TP2) and (TP3) are longer than first tissue path (TPI) by lengths of (TP2') and (TP3'), respectively. This additional length (TP2') and (TP3') in tissue adds additional impedance to second and third tissue paths (TP2) and (TP3), thus resulting in a higher current density at the leading edge 205 and a reduction in current density away from leading edge 205.

1000461 This phenomenon, known as "Leading Edge Effect," results in the concentration of energy and heat at the leading edge 205 of the return pad 200 and heating imbalance across the return pad 200. Leading Edge Effect may -result in serious injury to skin under the leading edge 205 if patient tissue "T' is heated beyond the point where circulation of blood can cool the tissue.

[00047] FIG. 2A is a cross-sectional view of a first embodiment of the present disclosure. Return pad 300 for providing, among other advantages, even heat distribution is formed of a conductive layer 310, an insulating layer 312 disposed on conductive layer 310, and an intermediate layer 320 placed between conductive layer 310 and contact layer 315. In one embodiment, intermediate layer 320 is formed of a thin dielectric material, such as, for example, a polyimide film sold under the trademark KaptonTm or a biaxially-oriented polyethylene terephthalate polyester film sold under the trademark MylarTM. In other embodiments, intermediate layer 320 may also be formed of a semi-conductive material, such as, for example, carbon, silicon, or germanium.

1000481 Intermediate layer 320 forms a low impedance connection with conductive layer 310 and contact layer 315. Low impedance connection may be formed by printing or silk screening the intermediate layer 320 on conductive layer 310.
Alternatively, conductive layer 310 may be printed or silk screened on intermediate layer 320. Low impedance connection may be formed by bonding conductive layer 310 and intermediate layer 320 with a suitable conductive adhesive or gel. Such conductive adhesive or gel can be made from, but is not limited to, a polyhesive adhesive, conductive hydrogel, a Z-axis adhesive or a water-insoluble, hydrophilic, pressure-sensitive adhesive.
Contact layer 315 forms a low impedance connection with intermediate layer 320.

(000491 With additional reference to FIG. 2B, the total impedance for a given pathway between the active electrode (not explicitly shown) and a return cable 318, through the return pad 300, includes the respective sum of the impedance of the tissue path (TP1), (TP2) and (TP3), the impedance of the adhesive paths (API), (AP2) and (AP3), the impedance of the conductive paths (CP I), (CP2) and (CP3) and the impedance of the intermediate path (IPI), (IP2) and (IP3). The additional impedance of the intermediate layer 320 evenly distributes the current flow through the return pad 300, thus reducing the current density at the leading edge 305 of return pad 300 or leading edge 305 of contact layer 315.

[000501 Intermediate layer 320 may also conduct heat generated by the current flowing through patient tissue "T" and the return pad 300. Areas of higher current density may generate hot spots on the return pad 300. Intermediate layer 320 evenly distributes energy, i.e. heat and/or current, thus lowering the temperature of hot spots on the return pad 300.

[000511 The impedance of the intermediate layer 320 may not be uniform.
Intermediate layer 320 may have greater impedance at leading edge 305 of return pad 300 and the impedance of the intermediate layer 320 may be reduced away from the leading edge 305. For example, the impedance of the first intermediate path (IPI) may be greater than the impedance of the second intermediate path (IP2), and the impedance of the third intermediate path (IP3) may be less than the impedance of first and second intermediate paths (IP1) and (IP2). Reduction in impedance of the intennediate layer 320 away from leading edge 305 may be gradual, linear or non-linear. The change in impedance may be accomplished by changing the material type, material density, material construction or any other suitable method or means for varying material impedance.

[00052] The varying impedance of the intermediate layer 320 may offset the difference in impedance of the various tissue pathways (TPI), (TP2) and (TP3).
As discussed hereinabove, the perpendicular "P" from the first tissue pathway (TP1) illustrates the additional impedance lengths of the second and third tissue pathway (TP2') and (TP3'). Varying the impedance of the internnediate layer 320 may equalize the impedance of the three illustrative pathways. For example, the impedance of the first and third illustrative pathways will be substantially the same if the sum of the impedance in tissue of (TP3') and the impedance of the third intermediate path (IP3) equal the impedance of the first intermediate path (IP 1). Similarly, the impedance of the first and second illustrative pathways will be equal if the sum of the impedance in tissue of (TP2') and the impedance of the second intermediate path (IP2) equal the impedance of the first intermediate path (IP 1).

[000531 Referring now to FIGS. 3A and 3B, a return pad 350 for providing, among other advantages, even heat distribution is shown and includes a conductive layer 310, an intermediate layer 320 and contact layer 315 larger than conductive layer 310.
Return cable 318 connects to conductive layer 310. Insulating layer 312 is disposed upon at least a portion of the conductive layer 310 and the intermediate layer 320.
Reduction in the size of the conductive layer 310 relative to intermediate layer 320 and contact layer 315 increases the impedance of current pathways away from the conductive layer 310.

1000541 With reference to FIGS. 2A and 3A, reducing the size of the conductive layer 310, as illustrated in FIG. 3B, does not change the impedance of the second intermediate path (IP2) because the pathway in the two embodiments is unchanged. The reduction of the size of the conductive layer 310 increases the impedance of the first intermediate path (IP I) because the conductive layer is spaced a distance away from the leading edge 305 while the impedance of the third intermediate path (IP3) is slightly increased.

[00055] The size and placement of the conductive layer 310, relative to the intermediate layer 320 and contact layer 315, impacts the impedance of the various cun-ent pathways. Positioning conductive layer 310 substantially in the middle of the intermediate layer 320 and contact layer 315 effectively increases the impedance of the pathways at the edges of the return pad 350. As illustrated in FIGS. 4A and 4B, positioning conductive layer 410 away from the leading edge 405, increases the impedance of the pathways at the leading edge 405 of the return pad 400, thus further reducing the current density at the leading edge 405 of return pad 400.

[00056] Referring back to FIG. 3A, decreasing the size of the conductive layer also increases the current density, and may result in the generation of heat at the connection between the intermediate layer 320 and the conductive layer 310.

[00057] Conductive layers 310, 410 may be formed as a single layer or may be formed as a plurality of sections separated by a barrier 330, 430, as illustrated in FIGS
3A-3C and 4A-4C. Barrier 330, 430 may be formed from a conductive material or altennatively, as described hereinbelow, barrier 330, 430 may be formed from a non-conductive or insulating material.

[00058] In yet another embodiment of the present disclosure, as illustrated in FIGS. 3C and 4C, contact layer 315 includes a plurality of contact layer sections 315a-d, 415a-d formed as a plurality of concentric rings or rows. FIG. 3C illustrates a concentric or substantially c'ucular return pad 350c, and FIG. 4C illustrates a rectangular shaped return pad 400c. Return pads 350c and 400c may be formed from any suitable shape, e.g., oblong, oval, hexagonal, or polygonal.

[00059] More particularly, FIG. 3C illustrates the return pad 350 of FIG. 3B
with the various portions of the contact layer 315 separated by barriers 330 formed of a non-conductive or insulating material. Contact layer 315 includes a center contact portion 315c, a first contact ring 315b, a second contact ring 315c, and an outer contact ring 315d with a barrier 330 between the adjacent portions.

(00060] FIG. 4C illustrates the return pad 400 of FIG. 4B with various portions of the contact layer separated by barriers 430 formed of an insulating material.
Contact layer 415 includes a first contact row 415a, a seeond contact row 415b, a third contact row 415c and an outer contact row 415d with a barrier 330 between the adjacent portions.
1000611 Barriers 330, 430 electrically isolate concentric rings 315a-d and rows 415a-d, respectively, thereby preventing current flow between rings 315a-d or rows 415a-d. Current enters the portion of the intermediate layer 320 above each concentric rings a-d or rows 415a-d. The current paths in contact layer 315 are substantially perpendicular to patient tissue "T" and the impedance of the intermediate paths will be different for each concentric ring 315a-d or rows 415a-d with the impedance of the pathways increasing as the distance away from the conductive layer 310 increases.

1000621 With reference to FIGS. 4A and 4B, leading edge 405 of return pad 400 is positioned closest to the active electrode (not explicitly shown) and conductive layer 410 is positioned away from leading edge 405. Current following the first tissue path (TPI) travels through outer contact row 415d, as illustrated by first contact path (AP1), and enters intermediate layer 415 toward the leading edge 405. Current travels across a substantial portion of the length of intennediate layer 415 as illustrated by first intermediate path (IP1), before entering conductive layer 410. Current foUowing the third tissue path (TP3) travels through first contact row 415A, as illustrated by third adhesive path (AP3), and enters intennediate layer 415 in close proximity to conductive layer 410. Current must only travel across the width of intermediate layer 420 before entering conductive layer 410. For both examples, current takes a substantially similar path through conductive layer 410, as illustrated by conductive path CP.

[00063] In one embodiment, the intermediate layer 420 may be formed of material with impedance properties substantially similar to the impedance properties of patient tissue "T". Matching the impedance properties of the intermediate layer 420 to patient tissue " T" results in substantially similar impedance for any given path between the active electrode (not shown) and return cable 418 through the return pad 400.

[00064] With reference to FIGS. 3A, 3B, 4A and 4B, backing layer 312 and 412, respectively, is disposed upon at least a portion of conductive layer and intermediate layer.

[00065] FIG. 5 illustrates yet another embodiment of the present disclosure having a return pad 500 that provides, among other advantages, even heat and current distribution andis formed of a first contact layer 515 having a first side adapted to couple to patient tissue "T" and a second side adapted to couple to a first side of intermediate layer 520. A second contact layer 525 engages second side of intermediate layer 520 to conductive layer 510. First and second contact layer can be made from, but is not limited to, a polyhesive adhesive, conductive hydrogel, a Z-axis adhesive or a water-insoluble, hydrophilic, pressure-sensitive adhesive. Insulating layer 512 is disposed upon the top portion of conductive layer 510 and return cable 518 connects to conductive layer 510.
[00066] Return Pad Cooling (000671 With reference to FIG. 6A, a cooled return pad 600a is shown and includes a contact layer 615, a conductive layer 610, a cooling layer 635 and a backing layer 640. Return cable 618 connects to conductive layer 610, which is formed of a suitable metal foil, dielectric material or dielectric / metal material combination. Cooling layer 635 and conductive layer 610 are configured in thermal communication such that energy, e.g., heat, is distributed and/or dissipated. Distribution and/or dissipation (herein referred to as distribution) of energy includes the transfer of energy between patient skin and/or the layers of the return pad 600a, the transfer of energy from the return pad to the surrounding area 642 and/or the transfer of energy between conductive layer 610 and cooling layer 635. Cooling layer 635 may be formed of an electrically non-conductive material andlor may be electrically isolated from conductive layer 610.

[00068] Cooling layer 635 may employ passive or active cooling techniques.
Passive cooling requires backing layer 640 to be formed from a breathable material that allows heat to dissipate from cooling layer 635 into surrounding area 642.
Active cooling may require backing layer 640 to be formed of impervious material to facilitate circulation of a cooling air or fluid. Backing layer 640 may form an air-tight or liquid-tight seal with conductive layer 610 or other portion of return pad 600a.

1000691 FIGS. 6B-6E illustrates several constructions of a cooled return pad with passive cooling. FIG. 6B illustrates cooled return pad 600b with a backing layer 640, contact layer 615, conductive layer 610, a return cable 618 connected to conductive layer 610 and a heat exchanger 636 as the cooling layer. Heat exchanger 636 may include a plurality of fins 636a to aid in the dissipation of heat. Heat exchanger 636 may be formed of any heat conducting material provided heat exchanger 636 is electrically isolated from conductive layer 610. Heat exchanger 636 may be formed of a heat conducting insulator, such as, for example a eeramic or dielectric material.
Backing layer 640 is disposed on or otherwise integrated with heat exchanger 636 and is formed of highly permeable material that allows heat to dissipate or exchange with surrounding area 642.

[00070] FIG. 6C shows yet another embodiment of the present disclosure having the cooling layer as an evaporative layer 637. Cooled return pad 600c includes evaporative layer 637 formed of a liquid or semi-liquid material with highly evaporative properties, such as, for example, alcohol or water, or alcohol or water-based gel.
Evaporative layer 637 absorbs heat from conductive layer 610 and heat is removed from cooled return pad 600c by evaporation, i.e. vaporization or evaporation of the evaporative material in evaporative layer 637. Top surface 610a of conductive layer 610 may foms ridges or fins 610b to increase the area of contact surface between conductive layer 610 and evaporative layer 637. Backing layer 640 is permeable to air.
Altematively, backing layer 640 may be permeable to air and impermeable to the material forming the evaporative layer 637. Backing layer 640 contains evaporative layer 637 between backing layer 640 and conductive layer 610 while allowing the vaporized gas to remove the heat. Backing layer 640 may be formed of a cloth or fabric treated with thermo-mechanically expanded polytetrafluoroethylene (PTFE) or other Fluoropolymer, such as the fabric treatment conunonly sold over the trademark Gore-TexTm or other porous hydrophobic materials or coating..

[00071] FIG. 6D shows yet another embodiment of the present disclosure having the cooling layer of the cooled return pad 600d composed of one or more Peltier devices 638, a well known device in the art that operates as a heat pump. In one embodiment, Peltier device 638 is formed by sandwiching a series array of small p and n type Bismuth Telluride cubes 638c between two metallizcd ceramic plates 638a and 638b that connect the cubes in series and applying a DC current, supplied from a DC power supply 638D, thereto. When a DC current is applied to the series array of small Bismuth Telluride cubes 638c, heat moves from one side of the Peltier device 638 to the other.
The cold side "C" cools the conductive layer 610 and the contact layer 610 and the hot side "H"
exchanges heat with the surrounding air 642. Peltier device 638 may also include a heat sink 638d to improve the cooling effect. Backing layer 640 is disposed on Peltier device 638 and is formed of highly permeable material that allows heat to dissipate or exchange with surrounding air 642.

[00072] FIG. 6E illustrates another embodiment of the present disclosure having a cooled return pad 600e with even heat distribution. More particularly, return pad 600e includes an intermediate layer 620, as illustrated in FIGS. 1-5 and disclosed hereinabove, and a cooling layer 635 as illustrated in FIGS. 6A-6D and 7-9 and discussed herein.
Interrmnediate layer 620 provides even current and hence even heat distribution and dissipation of energy and cooling layer 635 removes heat from the return pad 600e.

[00073] Cooled return pad 600e includes a backing layer 640, a cooling layer 635, a conductive layer 610, an intermediate layer 620 and a contact layer 615.
Conductive layer 610 is disposed between intermediate layer 620 and cooling layer 635.
Intermediate layer 620 is disposed between conductive layer 610 and contact layer 615.
Backing layer 640 is disposed upon at least a portion of cooling layer 635 and allows heat to dissipate or exchange with the surrounding air 642.

[00074] While FIGS. 6B-6E illustrate various passive techniques of cooling a return pad, other suitable techniques of passive cooling may be used.
Moreover, a passive cooling technique may be combined with one or more active cooling techniques as disclosed below.

[000751 With reference to FIG. 7, cooled return pad 700 includes a contact layer 715, a conductive layer 710, a retum cable 718 connected to conductive layer 710 and a backing layer 735. Backing layer 735 and conductive layer 710 fonn a cooling chamber 735a for circulating cooling fluid therewithin. Cooling chamber 735a may be further deffned by dimples 735b on backing layer 735. Dimples 735b are configured as spacers between contact conductive layer 710 backing layer 735 and provide cooling chamber with support and dimension. Edge 735c provides a seal between the layers forming the cooling chamber 735a and contains cooling fluid within cooling ehamber 735a.
Seal may be formed mechanically, i.e. clamping, crimping, etc., or by bonding, i.e.
adhesive, ultrasonic bonding, etc, or by other suitable sealing techniques.

[00076] Alternatively, dimples 735b may be formed by point or spot welding the layers that from the cooling chamber 735a. Cooling chamber 735a defines one or more fluid pathway "FP". Pump 740d supplies cooling fluid to inflow tube 740a, cooling fluid circulates through cooling chamber and outflow tube 740b retums cooling fluid to cooling system 740.

[00077] Cooling chamber 735a may also be defined by one or more channels formed in the backing layer 735 and/or conductive layer 710. Cooling chamber may be a single channel or chamber or may comprise a plurality of channels or chambers.

[00078] Cooling fluid may be purified water, distilled water or saline, although any suitable fluid, including air, may be used. Cooling system may also include a cooling module 740c, such as a refrigeration system, one or more Peltier device, vortex cooling device, heat exchanger, ice, etc. While FIG. 7 illustrates an active cooling technique for a return pad 700, other suitable active cooling techniques art may be utilized to accomplish the same purpose.

[00079] FIG. 8 shows a cooled return pad 800 that includes an intennediate layer 820 to provide even heat distribution as disclosed hereinabove. While many different variations and combinations are envisioned, FIG. 8 illustrates a particular embodiment with the even heat distribution pad, illustrated in FIG. 4A and 4B and disclosed hereinabove, incorporated into the cooled return pad 700 illustrated by FIG. 7 and described hereinabove.

[00080j Return pad 800 includes a contact layer 815, a conductive layer 810, an intermediate layer 820, and a cooling layer 835. Conductive layer 810 is disposed on intermediate layer 820. Altematively, conductive layer 810 may be disposed on only a portion of intermediate layer 820. As discussed hereinabove, the size and placement of the conductive layer 810 relative to the leading edge 805 of the pad 800 effects the impedance of the various current paths. Dimples 835b contact conductive layer and/or intermediate layer 820 and provide cooling chamber with support and dimension and define various fluid pathways "FP" in cooling chamber 835a. Pump 840d supplies cooling fluid to inflow tube 840a and outflow tube 840b returns cooling fluid to cooling system 840. Cooling module 840a may include a refrigeration system, a Peltier device, a vortex cooling device, a heat exchanger, ice, etc.

[000811 As disclosed hereinabove, intermediate layer 820 reduces the current density at the leading edge 805 of cooled return pad 800, dissipates energy and/or conveys heat from hot spots thus providing even heat distribution across the cooled return pad 800. Even distribution of heat across the cooled return pad 800 enables cooling system 840 to more efficiently remove heat and reduce the temperature of cooled return pad 800.

[000821 Seal along edge 835c is formed between conductive layer 810 and backing layer 835, and between intermediate layer 820 and backing layer 835. Cooling chamber 835a, formed between backing layer 835 and at least a portion of conductive layer 810 and a portion of intermediate layer 820, is configured to allow fluid to flow therethrough.
Seal along edge 835c may be formed mechanically, i.e. clamping, crimping, etc., or by bonding, i.e. adhesive, ultrasonic bonding, ete, or by other suitable sealing technique.
Cooling chamber 835a may be formed over intermediate layer, conductive layer or both.
[000831 FIG. 9 illustrates an electrosurgical system 900 including an electrosurgical generator 810, an active electrode 816, a cooled return pad 800 and a cooling fluid supply system 840. Electrosurgical generator 810 supplies electrosurgical energy to active electrode 816 through supply cable 814 and return pads 800 returns electrosurgical energy to electrosurgical generator 810 through return cable 818. Return cable 818 may also supply power DC power from the electrosurgical generator to cooling device in the return pads 800.

[000841 Cooling supply system 840 includes a cooling supply tube 841 that connects to a cooling supply 840c, a cooling return tube 842 that connects to the cooling return 840e and a pump 840d. In one embodiment, pump 840d supplies cooling fluid to the cooled retutn pads 800 through cooling supply 840 and cooling fluid supply tube 841.
Cooling fluid from the return pad 800 then returns to cooling system 840 through cooling fluid return tube 842 and cooling return 840e. Cooling supply system 840 may use any suitable supply for the cooling fluid, such as, for example, a saline drip bag or potable water supply. Cooling supply system 840 may circulate fluid thus relying on the ambient temperature to cool the fluid or cooling system supply 840 may include a variety of mechanism that are designed to cool the fluid, such as, for example, a refrigeration unit, a Peltier device, a heat exchanger, etc.

[000851 In use, a clinician connects supply cable 814 of electrosurgical return pad 800 to electrosurgical generator 810 and places return pad 800 in contact with patient "P"

skin. Cooling device on return pad 800 may be connected to an energy supply such as, for example, an electrical energy source (not shown) or a cooling fluid supply system 840. An active cooling layer or device on return pad 800 may be enabled by providing electrical power or cooling fluid flow. A passive cooling device or layer may be enabled by exposing the device or layer to ambient air. Electrosurgical generator 810 generates electrosurgical energy and supplies the electrosurgical energy to the patient via an active electrode 816.

[00086] Return pad 800 in electrosurgical system 900 may include one or more the above identified features in any of the embodiments of the present disclosure.

[000871 In yet another embodiment, cooling supply system 840 may include one or more chemicals that actively cool the return pads 800 in which the one or more chemicals may react to cool the return pads 800. For example, cooling supply tube 841 may include two lumens and may supply two fluids that create an endothermic reaction when released and combine in the cooling chamber. Cooling supply system may use other suitable methods of chemical cooling the return pad 800.

[40088] Return Pad Heattng [00089] FIGS. 10A-10C illustrate other embodiments of the present disclosure having heated return pads 1000, 1010. Heated return pads 1000, 1010 are configured in such a manner that the return pads are heated either prior to or atter applying the return pad to a patient.

[00090] With reference to FIG. 10A, heated return pad 1000 includes a heating layer 913 for heating at least a portion of the return pad 1000. As discussed hereinbelow, heating layer 913 may be an active heating layer, e.g., an electric heating means, or heating layer 913 may be a passive heating layer, e.g., one or more materials that create an exothermal chemical reaction. One purpose of the heating layer 913 is to preheat at least a portion of the contact layer 915 to a temperature similar to the temperature of patient's skin, typically between about 30 C and 35 C, thus eliminating or reducing patient discomfort that may be associated with adhering a cold return pad 1000 to patient's skin.

[000911 Heated return pad 1000 also includes a contact layer 915, a conductive layer 910, and a backing layer 912. A cable 918 connects to conductive layer 910 and, in some embodiments, may connect to heating layer 913. The composition and function of contact layer 915, conductive layer 910, and backing layer 912 are described hereinabove. Heating layer 913, as described hereinbelow may be incorporated into any of the embodiments described herein or any combination of embodiments.

[00092] Heating layer 913 may be in thermal communication with contact layer 915 through conductive layer 910, as illustrated in FIG. IOA. Conductive layer thermally conducts heat energy generated by the heating layer 913 from heating layer 913 to contact layer 915. Alternatively, at least a portion of heating layer 913 may be in direct contact with the contact layer 915 and thereby directly heat contact layer 915. In yet another embodiment, such as is illustrated in FIG. 10C, heating layer 913 may be at least partially positioned within contact layer 915 or the functionality of the heating layer 913 may be incorporated into contact layer 915.

[000931 FIG. 10B is a top view of the return pad 1000 of FIG. IOA (shown disposed within the active heating layer 913) and includes an electric heater element 913a and a substrate 913b. Electric heater element 913a may be disposed on substrate 913b or heater element 913a may be disposed between two substrates. One example of a suitable heater is a thermofoil heater manufactured by Minco under the trademark KaptonTm.
Substrate 913b may electrically insulate heater element 913a from conductive layer 910 while allowing heat energy to transfer from heating layer 913 to conductive layer 910.
[000941 Cable 918 is configured to supply electric current to heater element 913a from the electrosurgical generator or other suitable power source. Heater element 913a may also be a resistive-type heater and may be powered with AC or DC current.
For example, heater element 913a may be powered by the electrosurgical generator 110 with a frequency of about 500 kHz, 120 VAC or 50 VDC.

[000931 Various types of heaters could be used for the heating layer 913 provided the heater is sufficiently thin and insertable into return pad 1000 andlor sufficiently flexible as to not add an appreciable amount of stiffness to the return pad 1000. Heater element 913a (when disposed within the heater) may be formed from a single element, as illustrated in FIG. IOB, or heater may be formed with several heater elements arranged in parallel. For example, the thermofoil heater manufactured by Minco under the trademark Kapton'r"R has a suitable thickness of approximately 7 mils.

[000961 In yet another embodiment, as illustrated in FIG. IOC, heating element 913b is at least partially disposed in at least a portion of contact layer 915a and performs the function of the heating layer 913 in FIGS. IOA and IOB. Conductive layer 910 is disposed between the backing layer 912 and the contact layer 915.

[00097J Again with reference to FIG. 10A, other technologies may be employed to perform the same or similar functions as heating layer 913. For example, a chemical, exothennic pack (not shown) may be used to generate a sufficient amount of energy to heat the contact layer 915 to a target temperature. Exothennic pack may be manually activated, automatically activated when connected to the electrosurgical generator or activated when the retura pad is removed from the packaging.

1000981 In operation of one embodiment, heating layer 913 pre-heats the contact layer 915 prior to the application of the return pad 1000 to a patient's skin.
The contact layer 915 is pre-heated to a temperature about equal to, or slightly less than, the surface temperature of skin to prevent patient discomfort that may be experienced when the contact layer 915, at room temperature, or approximately 22 C, is placed on skin at the body temperature, or approximately 35 C.

[000991 Heating layer 913 is capable of providing a sufFicient amount of cnergy to heat contact layer 915 to a target temperature. The target temperature may vary based on the specific application and use. For example, the target temperature may range from 30 C to 35 C for application and use on a human and the upper limit may be as high as 39 C for veterinarian use.

[000100] The energy delivered by the heating layer 913, e.g., the rate of power delivered and/or the total amount of energy delivered, may be specifically matched to the size and/or volume of contact layer 915. For example, to heat and maintain a 3 X 3 inch return pad at a target temperature may require a lower rate of energy delivery and less total energy than what may be required to beat and maintain a 4 X 4 inch return pad.

[000101] The rate of power delivery and/or the total amount of energy delivered can be easily calculated if the energy source is chemical, such as, for example, an exothermic pack. The exothermic pack may only last for a few minutes and may provide a sufficient amount of heat energy to heat the contact layer 915 to the target temperature.
The heating capacity of the exothermic pack may be varied to match the size and/or volume of the contact layer 915.

[000102] A heating layer 913 that receives energy from an electrical energy source may require one or more safety featum to ensure that the temperature of the contact layer 915 does not exceed a target temperature. For example, with reference to FIGS.
lOB and IOC, temperature sensor 914b may be used to measure the temperatwe of the return pad. An electrical energy source, e.g., the electrosurgical generator 110, then controls the current to heating layer 913 to maintain return pad 1000 at a target temperature.

[000103] Various safety measures may be employed to insure that heating layer does not overheat heated return pad 1000. For example, one or more devices 914c may be incorporated in or associated with heating element 913a to interrupt or limit the current supplied to the heating element 913b. Device 914a may be a current limiting fuse, a thermal cut-off device, a timer-type device or any suitable device that may be incorporated ictto the circuit and/or system to prevent the return pad 1000 from exceeding the target temperature range.

[000104] Other safety measures may be incorporated into the electrosurgical generator 110. For example, electrosurgical generator 110 may employ existing circuitry to measure the temperature of the return pad or to measure the amount of current supplied to the heating element 913a Electrosurgical generator 110 may temlinate the supply of current when a predetermined temperature is obtained or after a predetermined amount of energy is supplied to the return pad 1000. Alternatively, new hardware and/or new software may be incorporated into the electrosurgical generator 110 to detect when a return pad 1000 is initially connected to the electrosurgical generator.
Connecting the return pad 1000 may cause the electrosurgical generator 110 to automatically heat the return pad 1000 for a predetetniined period of time or until a predetermined amount of energy is delivered to the return pad 1000. The predetermined period of time and predetermined amount of energy may be determined by the clinician or electrosurgical generator 110 may be configured to automatically determine or calculate the period of time based on the size and/or type of return pad.

10001051 Current supplied to the heating element 913a may be tenninated when the electrosurgical generator 110 detects that the return pad 1000 is in contact with tissue.
The return electrode monitor (REM) 112, or any other suitable contact quality system, may be used to determine when the return pad 1000 is in contact with patient tissue.

10001061 In use, return pad 1000 is connected to the electrosurgical generator 110.
Electrosurgical generator 110 automatically switches power to heater element 913a and supplies a low level current. Current is limited to an amount that will heat the return pad 1000 to a target temperature without resulting in an over-temperature condition. At least periodically, the REM 112 may be activated to determine if the return pad 1000 is applied to patient. After contact current to the heater element 913a is switched off, the return pad 1000 is enabled and the system is ready for activation. If temperature sensor 913b is present, temperature at the return pad 1000 may be measured and the current to the heater element 913a may be automatically adjusted by the electrosurgical generator 110 to maintain return pad 1000 at a target temperature. Safety devices 914c, if present, may disable the current flow if the return pad 1000 exceeds a maximum temperature.

[000107] In an alternative application, a heating layer, such as heating layer 913, may be employed on the back of a return electrode that could be used for patient heating.
Typically, patients are kept warm with blankets and/or water or air flow heating systems.
According to an embodiment of the disclosure, a large surface area pad, constructed with a backing layer, a thermofoil heater(s), and an adhesive hydrogel could provide a low profile solution to patient heating. The adhesive hydrogel may provide a uniform and comfortable contact area. Temperature sensing devices, such as thermistors or thermocouples, may be included in such a system to regulate temperature and ensure that the pad does not get too warm.

10001081 While several embodiments of the disclosure have been shown in the drawings, 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 wiU allow and that the specification be read likewise. For example, the return pad may include a plurality of electrodes or may include a plurality of novel intermediate layers. Therefore, the above description should not be construed as limiting, but merely as exemplifications of various embodiments.
Those skilled in the art will envision many other possible variations that are within the scope and spirit of the disclosure as defined by the claims appended hereto.

Claims

What is claimed is:

1. A return pad for use with an electrosurgical system, comprising:
a contact layer configured to engage patient skin;

a conductive layer disposed on the contact layer; and a heating layer, operatively associated with at least one of the contact layer and the conductive layer, the heating layer configured to heat the return pad.

2. The return pad according to Claim 1, wherein the heating layer includes at least one electric heating element configured to receive power from an external power supply.

3. The return pad according to Claim 2, wherein the external power supply limits the energy supplied to the at least one electric heating element to prevent the return pad from exceeding a target temperature.

4. The return pad according to Claim 3, wherein the return pad further includes a temperature sensor operable to sense the temperature of the return pad.

S. The return pad according to Claim 3, wherein the external power supply is operable to control the temperature of the return pad to at least one of reaching the target temperature and maintaining the target temperature.

6. The return pad according to Claim 2, further including at least one energy regulating device that prevents the return pad from exceeding a target temperature.

7. The return pad according to Claim 6, wherein the at least one energy regulating device is selected from a group consisting of a current limiting fuse, a thermal cut-off device, and a timer.

8. The return pad according to Claim 2, wherein the external power supply is an electrosurgical generator.

9. The return pad according to Claim 8, wherein the electrosurgical generator is operable to detect the connection to the return pad and automatically initiate energy delivery to the heating layer in response thereto.

10. The return pad according to Claim 1, wherein the heating layer includes an exothermic pack.

11. The return pad according to Claim 10, wherein the energy generated by the exothermic pack is operable to heat the return pad to about a target temperature.

12. The return pad according to Claim 11, wherein the energy generated by the exothermic pack is operable to limit heating the return pad to a temperature above the target temperature.

13. A return pad for use with an electrosurgical system, comprising:
a conductive layer; and a contact layer having a first side configured to engage patient skin and a second side disposed on the conductive layer; the contact layer including:

at least one electric heating element at least partially disposed in the contact layer, the at least one electric heating element configured to receive power from an external power supply;

wherein the electric heating element is configured to heat the contact layer to about a target temperature prior to engaging the contact layer to patient skin.

14. The return pad according to Claim 13, wherein the external power supply is operable to limit the energy supplied to the at least one electric heating element to prevent the contact layer from exceeding the target temperature.

15. The return pad according to Claim 14, wherein the return pad further includes a temperature sensor operable to sense the temperature of the return pad.

16. The return pad according to Claim 13, further including at least one energy regulating device operable to prevent the contact layer from exceeding the target temperature.

17. The return pad according to Claim 16, wherein the at least one energy regulating device is selected from a group consisting of a current limiting fuse, a thermal cut-off device, and a timer.