- Diathermy is the use of high frequency electric current to produce heat
- Used to either cut or destroy tissue or to produce coagulation
- Mains electricity is 50 Hz and produces intense muscle and nerve activation
- Electrical frequency used by diathermy is in the range of 300 kHz to 3 MHz
- Patients body forms part of the electrical circuit
- Current has no effect on muscles
Monopolar diathermy
- Electrical plate is placed on patient and acts as indifferent electrode
- Current passes between instrument and indifferent electrode
- As surface area of instrument is an order of magnitude less than that of the plate
- Localised heating is produced at tip of instrument
- Minimal heating effect produced at indifferent electrode
Bipolar diathermy
- Two electrodes are combined in the instrument (e.g. forceps)
- Current passes between tips and not through patient
Effects of diathermy
- The effects of diathermy depends on the current intensity and wave-form used
- Coagulation
- Produced by interrupted pulses of current (50-100 per second)
- Square wave-form
- Cutting
- Produced by continuous current
- Sinus wave-form
Risk and complications
- Can interfere with pacemaker function
- Arcing can occur with metal instruments and implants
- Superficial burns if use spirit based skin preparation
- Diathermy burns under indifferent electrode if plate improperly applied
- Channeling effects if used on viscus with narrow pedicle (e.g. penis or testis)
Bibliography
Aigner N,
Fialko C, Fritz A, Winks O, Zoch G. Complications in
the use of diathermy. Burns 1997; 23: 256-264.
Memon M A. Surgical diathermy. Br J Hosp Med 1994; 52: 403-407
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