Medical Diathermy

The electrosurgical current is used not only for the surgical application of cutting and coagulating body tissue, but also for muscular therapy, as used by physiotherapists. In this type of equipment, two equally large electrodes are attached to a patient and the electrosurgical current is passed between them. As the electrodes are equally large, the current density per square centimetre is very low, with the effect that the tissue between the electrodes rises in temperature, but does not cause tissue destruction (necrosis). The advantage with this kind of muscular therapy is that unlike external heating (which merely raises the temperature of the surface muscles) the electrosurgical current raises the temperature of the deep muscles not otherwise reached.

Electrosurgery (Surgical Diathermy)

If the current density per square centimetre is allowed to increase beyond the accepted safe level of 2.2 watts per square centimetre, then the heating effect of the current will reach a point where tissue destruction takes place by the explosive heating of cells.

In the surgical application of the diathermy current, this effect is encouraged by using a small electrode, and a large electrode (patient plate). Where the current leaves the small active electrode, the current density is very much higher than that at the larger patient plate electrode. Intense heating and tissue destruction takes place in the immediate vicinity of the smaller electrode with little effect on the rest of the intervening tissue.

The active electrode - the active electrode makes use of a wire loop, needle, blade or other configuration with a sharp contact point to concentrate the current flow through a few cells.

The cutting effect (which depends on current density) will be affected by the size of the surgical electrode used. A large electrode will disperse current flow over a larger surface than a small electrode. Large electrodes therefore require more current (i.e. higher power settings) to cut with the same speed and depth as small electrodes. Any electrode will cut if power is high enough to provide explosive heating of cells.