GB2130100A - Capacitively coupled indifferent electrode for electrosurgical procedures - Google Patents

Abstract

The electrode 10 includes a flexible backing sheet 12, an electrically conductive metal foil 14 adhered to one surface of the backing, and a dielectric layer 16, which is formed from pressure-sensitive adhesive, completely overlying the foil. The electrode is placed on a patient's skin and may be connected to the return side of an electrosurgical generator through a cable which is connected via a metal rivet 22 to the foil 14. The sheet 12 may be of closed cell foamed plastics material or of a fabric material, and the foil 14 may be aluminium. <IMAGE>

Description

1 GB 2 130 100 A 1

SPECIFICATION Capacitively coupled indifferent electrode

The present invention relates to medical electrodes used as indifferent electrodes in electrosurgical procedures, and more particularly to a capacitively coupled electrode having improved convenience, safety, and performance.

In electrosurgical procedures, an electrosurgical generator generates high radio frequency electric current which is fed to an active electrode. The active electrode is used to cut tissue and coagulate blood vessels and is activated for relatively short times during such procedures. An indifferent, or patient, electrode is placed in contact with a patient to provide a return path for 80 the high frequency current to the generator, which is in turn typically connected directly to ground or to an isolated ground unit.

The input current is applied to the tissue by means of the active electrode which is preferably of small cross-section so that high current densities may be obtained at the surgical site.

These high current densities provide the required heating (up to 1,0001C at the point of contact) needed for the operating procedure. However, it is essential that the indifferent electrode have contact over sufficient surface area of the patient to insure that the return current has a low density to avoid burning or scarring of the patient's tissue which is in contact with the indifferent electrode.

Prior art indifferent electrodes have either been of the direct electrical contact type or of the capacitively coupled type. Direct electrical contact type indifferent electrodes have either been designed to be attached directly to or placed 100 underneath a patient and have been available in both dry (direct metal contact to skin) and conductive gel or adhesive (electrode coupled to skin through a conductive solution, gel, or polymer) forms. However, direct electrical contact type electrodes suffer from a variety of problems.

For example, if a pre-gelled form is used, the gel may have dried out prior to use or may dry out during surgical use, there may be bacterial growth in the gel, and there are patient clean-up problems in rdmoving the gel after surgery. Additionally, the gel may cause skin irritation in some patients.

If a dry form direct electrical contact type electrode is utilized, usually in the form of a large surface area metal plate or foil, other problems 115 arise. These include the possibility of burns caused by preferential current flow due to patient perspiration or spilled fluids at the contact site, burns caused by the movement of the patient during surgery which breaks contact with a substantial portion of the metal surface, and electrical hazards to physicians and other operating room personnel if a protruding edge of the metal electrode is accidentally touched or comes in contact with other metal surfaces in the 125 operating room.

Moreover, all previous types of direct electrical contact type indifferent electrodes suffered from hot spots around their leading edges caused by a preference of radio frequency electrical current to leave a patient's body at those points. This uneven current distribution through the electrodes accentuates possible patient burning or scarring problems.

Capacitive coupled electrodes, on the other hand, have the potential of being much safer in use. These types of electrodes have a dielectric material sandwiched between the metal electrode and the patient's skin. In the past, these electrodes have been held in position on a patient's skin by elastic bands, strips of adhesive tape, or a peripheral adhesive area around the edges of the capacitor structure. However, these prior art methods of securing the electrode to the patient are unreliable. If a patient is moved or repositioned, air gaps or tenting causes portions of the dielectric material to pull away from a patient's skin, creating hot spots and possibly causing burning or scarring of tissue. Accordingly, the need still exists in the art for a convenient, safe, and reliable indifferent electrode for use in electrosurgical procedures.

The present invention consists in a capacitively coupled indifferent electrode for use in an electrosurgical procedure, comprising a thin, flexible electrically conductive foil mounted on a flexible backing sheet, means for electrically connecting the foil to an electrosurgical current generator, and a layer of pressure-sensitive adhesive, which also serves as a dielectric layer, disposed 'in contact with and completely overlying the electrically conductive foil and forming a skincontacting surface which is capable of capacitive coupling under electrosurgical conditions.

Conveniently, the electrical connecting means comprises a metal rivet piercing the conductive foil and passing through to the opposite side of the backing sheet, for example, a foam pad, where it is mated with a metal socket which is then crimped to grip and hold the rivet. The metal socket can then be snap fitted to an electrical cable means which is in turn connectable to the return side of an electrosurgical current generator. In another embodiment, an electrical cable and plug may be pre-attached to the foil.

The conductive foil is completely covered by the layer of pressuresensitive, dielectric adhesive and this adhesive attaches itself securely to the conductive foil and also serves to attach the electrode securely to a patient's skin, upon removal of a protective releasable cover sheet, if provided.

In use, the protective releasable cover sheet, when provided, is peeled away and the electrode assembly is placed on the patient adhesive side down. The adhesive layer prevents any gaps or voids from forming and assures continuous contact of the dielectric layer over the entire surface area of the electrode providing uniform electrical coupling to the skin. The shape of the electrode assembly is not critical, and it may be fabricated in a variety of different shapes adapted to be adhered to different portions of a patient's body. Typically, the assembly will have a 2 GB 2 130 100 A 2 rectangular configuration.

In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which:

Fig. 1 is an exploded perspective view of one embodiment of indifferent electrode according to the invention, and Fig. 2 is a sectional side view of the assembled indifferent electrode.

Referring to Figs. 1 and 2, a capacitively coupled indifferent electrode 10 is shown.

Although a rectangular configuration is illustrated, it has been found that the shape of the electrode is not important and can be a variety of shapes. The 75 electrode includes a flexible, resilient backing material 12, a metal foil layer 14, a continuous layer 16 of non-conductive pressure-sensitive adhesive, which also serves as a dielectric layer, and a protective cover sheet 18 releasably attached to the face of the layer 16. One surface of the backing material 12 is covered with a layer of a commercially available medical grade acrylic pressure-sensitive adhesive 20. Metal foil layer 14 is then adhered to adhesive 20. The foil layer 14 and material 12 are then pierced by a metal rivet 22 having a shaft 24. Shaft 24 is of sufficient length to pass through both the metal foil layer 14 and backing material 12 and is mated with a metal socket 26 to provide an electrically conductive path through the pad. Socket 26 is then crimped to lock the shaft in place. Socket 26 can then be easily snap fitted to a return line of an eiectrosurgical generator. Alternatively, any suitable means to provide an electrically conductive path from foil layer 14 to the return side of an electrosurgical generator may be utilized.

A button 28 of an electrically non-conductive material such as nylon or other insulating material is interposed between rivet 22 and the adhesive dielectric layer 16 to ensure that the rivet will never come into direct contact with a patient's skin. The layer 16 may be of any suitable electrically non-conductive material which can be easily formed into a thin adhesive film. It is 105 important that the layer 16 at least cover to the edges of the metal foil so that there is no exposed metal on the electrode. Although the electrode illustrated in Figs. 1 and 2 has a backing material 12 with a surface area larger than metal foil layer 110 14, it is within the scope of the invention to provide dielectric and metal foil layers which extend to the edges of the backing pad. In this manner, the entire surface area of the apparatus is used.

Backing material 12 is preferably formed of a closed cell foamed plastics material, such as polyurethane, polyvinyl chloride, or the like. Such materials will resist absorption of fluids.

Alternatively, the backing material may be a fabric 120 material. Such a sheet is quite flexible and readily conforms to skin contours. Foil 14 may be fabricated of any suitable electrically conductive material which can be made into a thin, flexible foil, aluminium foil being preferred.

The capacitively coupled electrode of the present invention provides both safe and reliable operation. Because the adhesive covers the entire surface of the electrode, it provides much more secure contact with a patient's skin and resists tenting or the formation of air gaps which could cause hot spots. Additionally, there is no requirement for a peripheral ring of adhesive around the edges of the electrode; the entire surface area can be utilized for an electrode surface. Electrodes having surface areas of 193.5 sq cm (30 square inches) or more can be operated at high currents for up to 1 minute and still not create any dangerous rise in a patient's skin temperature. Because of the exponential heat rise with decreasing electrode size, a 96.8 sq cm (15 square inch) electrode appears to represent the practical limits for safe usage. However, even smaller size electrodes would have utility in controlled current applications.

Claims (9)

1. A capacitively coupled indifferent electrode for use in an electrosurgical procedure, comprising a thin, flexible electrically conductive foil mounted on a flexible backing sheet, means for electrically connecting the foil to an electrosurgical current generator, and a layer of pressure- sensitive adhesive, which also serves as a dielectric layer, disposed in contact with and completely overlying the electrically conductive foil and forming a skincontacting surface which is capable of capacitive coupling under electrosurgical conditions.

2. An indifferent electrode as claimed in claim 1, in which the flexible backing sheet has a peripheral portion extending beyond the edges of the conductive foil, said peripheral portion having pressure-sensitive adhesive thereon.

3. An indifferent electrode as claimed in claim 1, in which the conductive foil extends substantially completely to the edges of the flexible backing sheet.

4. An indifferent electrode as claimed in claim 1, 2 or 3, in which the conductive foil has a surface area of at least 96.8 sq cm.

5. An indifferent electrode as claimed in any one of the preceding claims, in which the conductive foil comprises aluminium.

6. An indifferent electrode as claimed in any one of the preceding claims, in which the flexible backing sheet is fabricated from a polymeric foam material.

7. An indifferent electrode as claimed in any one of the preceding claims 1 to 5, in which the flexible backing sheet is fabricated from a fabric material.

8. An indifferent electrode as claimed in any j7 c W 1 1 3 GB 2 130 100 A 3 one of the preceding claims, in which the electrical substantially as hereinbefore described with connecting means is a snap fastener. 5 reference to the accompanying drawings.

9. A capacitively coupled indifferent electrode Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1984. Published by the Patent Office, 25 Southampton Buildings, London, WC2A IlAY, from which copies may be obtained.