Current and Apparatus of Surgical Diathermy

Desiccation produces destruction by a drying up of the part or lesion. The Oudin current is of relatively low amperage and high voltage, in which the return flow of current from the patient to the machine is probably through electromagnetic waves, so that the terms monoterminal" and "uniterminal" which have been applied to it are in a sense misleading. Desiccation is accomplished by the application of this type of current through a metallic needle touching or inserted into the tissues. The high voltage, low amperage, and the number and character of the oscillations produce a very superficial destruction. Coagulation is generated by a rapidly oscillating biterminal low voltage current of high amperage of sustained and damped oscillations especially produced for the purpose. One terminal is connected to an indifferent electrode and the other is attached to the active electrode which is held against or inserted into the diseased tissue. Desiccation does not necessarily mean treatment with a uniterminal current, and coagulation with a biterminal, because heavy uniterminal currents may produce some coagulation and mild biterminal currents may cause only desiccation.

            Cutting is produced by a continuous undamped oscillating current. Undamped oscillations are of equal intensity and amplitude. In some machines used for cutting, continuous undamped oscillations are obtained by the introduction of a radio tube. Other machines approximate continuous undamped oscillations by a proper balance of the induction coils, spark gap, and the capacity of the condenser.