GB1601588A - Diathermy electrode - Google Patents

Description

(54) DIATHERMY ELECTRODE (71) We, DRG (U.K.) LIMITED, a British Company, of 1 Redcliffe Street, Bristol BS99 7QY, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a diathermy electrode.

Diathermy or electrosurgery is a technique in which living tissue is cut and/or coagulated by means of a high frequency alternating electrical current. It is in widespread use in many types of surgical procedure. The alternating current passed through the tissue is of radio frequency, typically of the order of 500 khz to 1.75 mhz and the cutting and/or coagulation results primarily from heat generated as a result of tissue resistance to the passage of the current. Cutting is effected by passage of a sinusoidal current which causes the cells to dehydrate and explode rapidly to give a clean incision. Coagulation is effected by passage of a current having a damped pulse wave form which causes more thermal heating and brings about slower dehydration of the cells resulting in coagulation.

Diathermy is carried out by application to a patient of two electrodes one of which is held by the surgeon ("the active electrode") while the other returns the current to earth ("the return electrode or patient plate").

The amount of heat communicated to the patient by each electrode depends on the size thereof, the smaller electrode imparting the greater amount of heat because it produces a higher current density. In diathermy, therefore, the active electrode is usually small and the patient plate is large. It is desirable for the patient plate to make electrical contact with a large area of the patient's skin otherwise there may be excessive skin heating resulting in burns. Diathermy machines are therefore typically equipped with a patient circuit safety monitoring system connected to the patient plate and arranged to give an alarm signal in the event of abnormal patient contact conditions.

Until recently the commonly used patient plate consisted of a lead plate wrapped in saline-soaked gauze and strapped to the patient's leg or some other part of the body. This arrangement was inconvenient and suffered from the disadvantage that if the gauze dried out during the operation a severe burn could result. More recently used patient plates are disposable or of limited life and are based on metal foil but these types also suffer from disadvantages. In particular there is difficulty in ensuring that a sufficient area of the plate is in contact with the patient, wrinkling or distortion thereof significantly reducing the area of contact. Also cracks in the foil render a large area of the plate inoperative without completely destroying the electrical contact to the patient. Such cracks arise because a single patient plate is often used for a number of different patients and the plate has to be removed from one patient, straightened and then applied to another patient. The repeated bending and flexing of the foil together with the removal process is liable to give rise to fatigue cracks.

It is an object of the invention to provide a disposable patient plate for diathermy apparatus which is inexpensive to manufacture and is safe in use.

The present invention provides a patient plate for diathermy apparatus comprising a sheet of flexible electrically insulating material, and a metal foil secured to one face of the sheet of insulating material, the metal foil having a contact edge for connection to diathermy apparatus, a slot in the foil extending from the contact edge towards an opposing edge of the foil for a major portion of the distance between said edges, whereby the foil defines a generally U-shaped pattern. Preferably there is a coating of pressure sensitive adhesive on said face of the sheet of insulating material, by which the foil is secured to the sheet, the coating being exposed at least through the slot. The slot then functions both to expose an underlying area of adhesive to promote contact between the electrode and the skin and to enable cracks in the electrode to be detected more readily. The crack detector functions by means of a monitoring circuit provided in the diathermy machine and arranged to make electrical contact with the plate to either side of the slot and respond to changes of electrical resistance therebetween. Apertures in the metal foil may provide additional exposed areas of adhesive which further promote contact between the electrode and the skin.

The assembly of insulating material and foil may be protected prior to use by means of a removable protective sheet over the foil on said face of the insulating sheet, covering the exposed coating.

The preferred embodiment of patient plate according to the invention has the advantages that it is easy and convenient to apply and is formed in soft pliable material for added patient safety. The insulating backing sheet protects the operating theatre staff against accidental shocks. Furthermore the plate can be fitted to patient plate holders of existing diathermy machines.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an end view of an electrode assembly and protective sheet; Figure 2 is a plan view of the electrode assembly; and Figure 3 is an oblique exploded view of the electrode assembly.

A generally rectangular sheet of flexible foamed plastics material 10 typically a closed cell polyvinyl chloride foam such as is marketed under the trade name INSEAL (Registered Trade Mark) is coated on one face with a hypo-allergenic permanently tacky or pressure sensitive adhesive to which is adhered a rectangular aluminium foil electrode 11 of slightly smaller length and width than the plastics sheet and 25 of area about 200 sq. cms. An end edge 12a on the foamed plastics sheet is positioned in register with an edge 1 2b on the electrode to define a common contact edge having perforations 13 dimensioned and positioned to receive fastening studs of a patient plate holder (not shown) of a diathermy apparatus. Extending longitudinally from the contact edge towards the opposing edge is a slot 14 in the electrode.

This extends for a major portion of the distance between the edges so as to define a U-shaped pattern in the foil electrode. To either side of the slot are formed perforations 15 and 1 spa disposed in rows which also help to maintain good contact between the electrode and the skin.

Prior to use the electrode 11 and backing sheet 10 are protected by means of a cover sheet 16 of release coated paper.

In use the protective backing sheet 16 is peeled off and the electrode is fitted into the patient plate holder, a first electrical contact being established between the perforations 13a to one side of the slot 14 and a second electrical contact being established between the perforations 1 3b to the other side of the slot. The electrical pathway between the first and second contact point is generally U-shaped and extends to the far edge of the electrode. It will be appreciated that the electrical resistance between the first and second contact points is sensitive to cracks in the electrode and the degree of sensitivity is increased because the slot 14 causes the pathway therebetween to be indirect and extend through the body of the electrode.

Various modifications may be made to the embodiment described above without departing from the invention. For example the cellular electrically insulating material 10 may be replaced by a sheet of flexible non-woven textile material. The aluminium foil used may be laminated to a very thin plastics foil, the resulting laminated material being contacted with the coating of tacky or pressure sensitive material on the sheet of flexible insulating material. The use of aluminium foil laminated to plastics foil rather than aluminium foil alone enables the thickness of the aluminium layer to be reduced. For example, the total thickness of the laminated material may be 28 microns of which about 10 microns accounts for the aluminium layer and 18 microns accounts for the plastics foil layer. Such a material gives greater conformity to the patients body and helps to increase the area of contact.

WHAT WE CLAIM IS: 1. A patient plate for diathermy apparatus, comprising a sheet of flexible electrically insulating material, and a metal foil secured to one face of the sheet of insulating material, the metal foil having a contact edge for connection to diathermy apparatus, a slot in the foil extending from the contact edge towards an opposing edge of the foil for a major portion of the distance between said edges, whereby the foil defines a generally U-shaped pattern.

2. A patient plate according to Claim 1 in which there is a coating of permanently tacky or pressure sensitive adhesive on said face of the sheet of insulating material, by which the foil is secured to the insulating sheet, the coating being exposed at least through the slot whereby in use the coating adheres the patient plate to the patient.

3. A patient plate according to Claim 2 wherein apertures are provided in the foil to either side of the slot, further areas of said coating being exposed through the apertures.

4. A patient plate according to Claim 2 or Claim 3 having a removable protective sheet over the foil on said face of the insulating sheet, covering the exposed coating.

5. A patient plate according to any one of the preceding claims wherein the insulating sheet is a sheet of closed cell polyvinyl chloride foam.

6. A patient plate according to any one of the preceding claims wherein the metal foil is an aluminium foil.

7. A patient plate substantially as described herein with reference to the accompanying drawings.

8. Diathermy apparatus, comprising a patient plate according to any one of the preceding claims, and resistance monitoring means, the resistance monitoring means being connected to the contact edge of the foil on each

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. the electrode and the skin. The assembly of insulating material and foil may be protected prior to use by means of a removable protective sheet over the foil on said face of the insulating sheet, covering the exposed coating. The preferred embodiment of patient plate according to the invention has the advantages that it is easy and convenient to apply and is formed in soft pliable material for added patient safety. The insulating backing sheet protects the operating theatre staff against accidental shocks. Furthermore the plate can be fitted to patient plate holders of existing diathermy machines. An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an end view of an electrode assembly and protective sheet; Figure 2 is a plan view of the electrode assembly; and Figure 3 is an oblique exploded view of the electrode assembly. A generally rectangular sheet of flexible foamed plastics material 10 typically a closed cell polyvinyl chloride foam such as is marketed under the trade name INSEAL (Registered Trade Mark) is coated on one face with a hypo-allergenic permanently tacky or pressure sensitive adhesive to which is adhered a rectangular aluminium foil electrode 11 of slightly smaller length and width than the plastics sheet and 25 of area about 200 sq. cms. An end edge 12a on the foamed plastics sheet is positioned in register with an edge 1 2b on the electrode to define a common contact edge having perforations 13 dimensioned and positioned to receive fastening studs of a patient plate holder (not shown) of a diathermy apparatus. Extending longitudinally from the contact edge towards the opposing edge is a slot 14 in the electrode. This extends for a major portion of the distance between the edges so as to define a U-shaped pattern in the foil electrode. To either side of the slot are formed perforations 15 and 1 spa disposed in rows which also help to maintain good contact between the electrode and the skin. Prior to use the electrode 11 and backing sheet 10 are protected by means of a cover sheet 16 of release coated paper. In use the protective backing sheet 16 is peeled off and the electrode is fitted into the patient plate holder, a first electrical contact being established between the perforations 13a to one side of the slot 14 and a second electrical contact being established between the perforations 1 3b to the other side of the slot. The electrical pathway between the first and second contact point is generally U-shaped and extends to the far edge of the electrode. It will be appreciated that the electrical resistance between the first and second contact points is sensitive to cracks in the electrode and the degree of sensitivity is increased because the slot 14 causes the pathway therebetween to be indirect and extend through the body of the electrode. Various modifications may be made to the embodiment described above without departing from the invention. For example the cellular electrically insulating material 10 may be replaced by a sheet of flexible non-woven textile material. The aluminium foil used may be laminated to a very thin plastics foil, the resulting laminated material being contacted with the coating of tacky or pressure sensitive material on the sheet of flexible insulating material. The use of aluminium foil laminated to plastics foil rather than aluminium foil alone enables the thickness of the aluminium layer to be reduced. For example, the total thickness of the laminated material may be 28 microns of which about 10 microns accounts for the aluminium layer and 18 microns accounts for the plastics foil layer. Such a material gives greater conformity to the patients body and helps to increase the area of contact. WHAT WE CLAIM IS:

1. A patient plate for diathermy apparatus, comprising a sheet of flexible electrically insulating material, and a metal foil secured to one face of the sheet of insulating material, the metal foil having a contact edge for connection to diathermy apparatus, a slot in the foil extending from the contact edge towards an opposing edge of the foil for a major portion of the distance between said edges, whereby the foil defines a generally U-shaped pattern.

2. A patient plate according to Claim 1 in which there is a coating of permanently tacky or pressure sensitive adhesive on said face of the sheet of insulating material, by which the foil is secured to the insulating sheet, the coating being exposed at least through the slot whereby in use the coating adheres the patient plate to the patient.

3. A patient plate according to Claim 2 wherein apertures are provided in the foil to either side of the slot, further areas of said coating being exposed through the apertures.

4. A patient plate according to Claim 2 or Claim 3 having a removable protective sheet over the foil on said face of the insulating sheet, covering the exposed coating.

5. A patient plate according to any one of the preceding claims wherein the insulating sheet is a sheet of closed cell polyvinyl chloride foam.

6. A patient plate according to any one of the preceding claims wherein the metal foil is an aluminium foil.

7. A patient plate substantially as described herein with reference to the accompanying drawings.

8. Diathermy apparatus, comprising a patient plate according to any one of the preceding claims, and resistance monitoring means, the resistance monitoring means being connected to the contact edge of the foil on each

side of the slot so as to monitor the resistance of the U-shaped pattern defined by the foil.