Med. & Biol. Engineering, Vol. 7, pp. 341-343, Dec. 28, 1968..
What we claim is
1. A plate electrode device for use in surgery comprising a thin flexible metal foil sheet electrode, a thin flexible plastic electrically non-conductive backing superimposed on a face of said metal foil sheet, a pair of transversely spaced, parallel, longitudinally extending flexible metal foil band conductor leads integrally formed at their inner ends in one piece with said metal foil sheet and extendable therefrom, said conductor leads being spaced from one another throughout their entire length, a thin flexible electrically non-conductive backing superimposed on one face of and joining said pair of metal foil bands and an electrically insulating layer covering the other face of said bands.
2. The plate electrode device of claim 1 wherein said sheet electrode and bands are substantially coplanar and said pair of bands are spirally wound about said electrode.
3. The plate electrode device of claim 2 wherein the confronting edges of successive convolutions of said band pair are separably joined.
4. The plate electrode device of claim 1 including electrical coupling elements connected to the outer ends of said bands.
5. A plate electrode as claimed in claim 1, wherein the electrode is of aluminum foil and the backing is of a polyester.
6. A plate electrode as claimed in claim 1 wherein the electrode is of copper and the backing is of polyester.
BACKGROUND OF THE INVENTION
Diathermy is a process by which heat is developed in the human body by the passage of a high frequency alternating electric current. A typical surgical diathermy apparatus has two electrodes. One of these electrodes is called the active electrode and is the electrode used for cutting and coagulating the tissue. This electrode has a very small surface area and the current passing from this electrode to the tissues has an intense heating effect. The other electrode is necessary to complete the electrical circuit and is termed the indifferent ground or plate electrode. This electrode is much larger in area than the active electrode in order to reduce the current intensity and therefore its heating effect. In order to prevent the occurrence of burns, it is important that a high proportion of the area of the plate electrode is maintained in good electrical contact with the skin.
Plate electrodes are usually of lead or stainless steel which can be moulded to conform to the sites of application to the patients, usually the thighs. To maintain good contact with the skin, the plate electrode is placed in a gauze bag and dipped in saline solution before use. Conductive creams or jellies may also be used in the case of stainless steel plates. When a lead plate has been bent a number of times, it tends to become corrugated, so that the larger area of contact is reduced to a number of ridges, and this can lead to burns at the site of the plate electrode. Such burns may be very serious.
The conventional plate electrodes also suffer from other disadvantages. Thus, the connecting lead to the diathermy apparatus has to be fitted on to the plate with a connector or attachment of some sort, and this always involves the possibility of bad electrical contact or breakage, which may also result in the patient being burnt. The high thermal mass of the conventional plates in particular large, thick lead plates, combined with the cooling effect of the saline, can produce a serious fall in body temperature in the treatment of infants and young children. Furthermore, lead plates are very heavy, and there is always the danger that they will slip out of place if not bound firmly to the patient.
An object of the present invention is to provide a plate electrode which avoids the disadvantages of known plate electrodes.
SUMMARY OF THE INVENTION
A plate electrode according to the present invention comprises a thin and flexible sheet of metal foil backed by a flexible film of plastics material. The thickness of the metal foil and the plastics material is not important provided the laminated structure which forms the plate electrode is flexible and has adequate strength. Preferably, the electrode has at least two integral conductor leads which are also of flexible metal foil backed by a flexible plastics film. The conductive metal foil of the leads is covered with a flexible insulating film except for terminal portions which can be inserted in a connector which may be in the form of an adaptor.
The electrode may be of any shape, e.g., square, rectangular, or circular. Different shapes may be more convenient for certain sites on the body, and for different methods of attachment.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of an electrode according to the invention, and
FIG. 2 is a section to a greatly exaggerated scale.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
An electrode 1 is of circular shape with a diameter of about 15 centimeters. The electrode consists of a thin, flexible and conductive metal foil with a backing 2 of thin flexible plastics material. Such an electrode has the great advantage over conventional plate electrodes that it is very flexible and always provides excellent electrical contact with the skin of the patient over the whole surface area of the electrode. The electrode plate is used dry, eliminating the need of saline contact solution or jelly. The electrode is also very light in weight and may be easily and securely fitted to the patient by means of an adhesive plaster or a bandage or the like.
The metal foil 1 can be of any convenient conductive material. It may, for example, be of copper or aluminum or stainless alloy. The backing 2 may be of any suitable flexible plastics film such as polyvinyl chloride, polyethylene, or a polyester such as that known under the registered trade mark of Mylar.
The electrode is preferably provided with two integral flexible conductor leads 3 or 4. More than two leads can be provided if desired. Where two leads are provided, both leads are made of flexible metal foil backed by flexible plastics film and the conductive metal foil may have a covering 5 of insulating material. The insulating covering 5 to the conductor lead may conveniently be of any flexible plastics film material such as polyvinyl chloride, polyethylene or a polyester, or it may be of a plastics coating applied in liquid form.
The purpose of a second conductor lead is to enable the electrical continuity of the plate electrode to be monitored continuously, by passing a small electrical current down one of the conductors to the plate electrode and back via the other conductor through a current sensing circuit, which may be arranged to provide a warning signal if there is a discontinuity in the plate circuit. This current is a secondary current which is not in any way connected with the high frequency diathermy current.
The leads 3 and 4 have terminal portions 6 and 7.
The plate electrode may be made by first producing a laminate consisting of a flexible metal foil backed by the flexible plastics material after which the electrode and, if desired, its lead is produced simply by cutting it out of the laminated sheet. However, the electrode and its lead are advantageously manufactured by printed circuit techniques. For example the metal foil of the laminate can be etched to the desired shape, after first covering the required metal area with an etch resistant coating.
An advantage of using an etching technique instead of the mechanical cutting is that as shown in the drawing, a border 8 of non-conducting plastics material is left surrounding the metal foil of the electrode and the integral lead. This provides an insulated edge to the lead conductor or conductors to prevent accidental contact with other apparatus or with the body of the patient.
It has been found both convenient and economical to produce the conductor leads 3 and 4 in the form of a coil or coils surrounding the plate electrode. In such a case, a portion of the plastics film of the backing may extend between adjacent coils and may be cut in a continuous spiral which upon extension forms a longitudinally extending lead of sufficient length (approximately 2 meters) to reach from the diathermy generator to the patient. Preferably however, thin radial portions or "bridges" of the plastics film may be left between adjacent turns sufficient to hold the coils in position for packing, but which will break if pulled, to allow the lead to be extended.
After the electrode and its lead has been produced in this manner, they may be backed by a suitable material to keep the lead in position for packing and storage purposes until the electrode is required for use when the backing material is removed to allow the leads to be extended.