ELECTRIC EQUIPMENT 6 Surgical Diathermy

Surgical Diathermy

Surgical diathermy is an equipment that generates a high- frequency current. The patient is connected to a large contact electrode. The other electrode is small.

•     when the current is passed through the patient’s body between two electrodes, the effect is to produce a concen­tration of current at the smaller electrode in the hand of the surgeon

•     As the surgeon applies his ‘live’ (small) electrode to the tissues, the current passes through the touched tissue cells and owing to the tissues electrical resistance, heat is generated at this small contact point (Fig. 2.3A)

•     The effect is localized because with monopolar system the current from the‘live’(small) electrode spreads out in the patient’s body and travels to the ‘indifferent’ electrode which is a large electrode placed in contact with the patient’s body (thigh or sacrum)

•     A high density of current occurs only immediately beneath the live electrode because further away (except under fault conditions) the current density is too small to have any heating effect.

             The purpose of the indifferent large surface electrode is to provide a surface of sufficient area to avoid any heat effects at this site.

•     This is because the indifferent electrode is in contact with hundreds or even thousands more cells than the live electrode which results in a correspondingly lower density of current in each cell

•     If the electrode is applied correctly as described below, negligible heat is generated in this area

•     The commonest types of indifferent electrode is a flexible metal plate. The thin flexible metal plate electrode can either be placed under the patient’s body (sacrum) or carefully bandaged round the thigh to ensure even wide contact with the skin

•     It is unnecessary to use electrode jelly, though if the patient is hairy, shaving beforehand is advisable—as hair acts as an electrical resistance

•     If the patient’s skin is dry, moistening with water or saline and can be used with advantage before applying the plate.

•     Replace a plate electrode which becomes buckled otherwise areas of irregular contact with the skin result which could allow points of high current density and risk of burns

•     The electrode is connected to the high frequency electrosurgical unit indifferent or earth terminal by a heavy insulated wire.

      With bipolar system the surgeon’s instrument, usually in the form of a forceps, combines both electrodes so that current flows down both limbs of the forceps and thus only through the tissue gripped between the tips of the forceps, thereby eliminating the need for an indifferent electrode

 

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