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Key Facts - Diathermy

Created: 30/7/2005



  • Diathermy involves the passage of high-frequency alternating current (AC) through body tissue
  • Where the current is concentrated heat is produced and heat, up to 1000°C, is produced
  • Low frequency AC (eg mains – 50Hz) causes neuromuscular stimulation. The response disappears above 50,000Hz/5KHz
  • Diathermy involves frequencies between 400KHz – 10MHz
  • Currents up to 500mA pass safely through the body

Monopolar diathermy

  • Most common
  • High frequency current from diathermy generator is delivered to the active electrode (“diathermy forceps”) held by surgeon
  • Current density is high where active electrode touches tissue producing localised heating
  • Current then spreads through body, and returns to generator via patient plate electrode
  • NB Plate contact with patient should be at least 70cm2

Bipolar diathermy

  • Avoids need for plate
  • Current passes down one limb of forceps through small piece of tissue to be coagulated, and then back to generator via other limb of forceps
  • NB Cannot be used for cutting, or “buzzing” other forceps

Cutting diathermy

  • Involves continuous output from generator
  • An arc is struck between active electrode and tissue
  • Temperatures up to 1000°C are produced, vaporising water, causing tissue disruption with some blood vessel coagul;ation

Coagulating diathermy

  • Involves a pulsed outpur
  • Causes dessication and sealing of blood vessels with minimal tissue disruption

  • NB “blend” allows combination of cutting and coagulation waveforms to increase haemostasis during cutting. Only functions in cutting mode



Main causes of diathermy burns:

  • Incorrect positioning of patient plate
    • Should be sited close to operation site with current moving away from ECG
    • Plate should avoid bony prominences and scar tissue
    • Skin should have a good blood supply
    • Skin should be shaved
    • Plate must have good skin contact
    • Skin prep should not seep under plate
  • The patient
    • Patient should not touched earthed metal objects eg drip stands, parts of operating table
  • Careless technique
    • Check diathermy settings
    • Allow spirit-based skin prep to evaporate
    • Individual with active electrode should only activate the machine
    • If diathermy performance is poor, plate and lead should be checked
    • Beware of diathermy on gut or appendages


  • High-frequency current can interfere with pacemakers causing arrhythmias or even arrest
  • Current can travel down pacemaker wire, causing myocardial burn
  • If considering diathermy in a patient with a pacemaker cardiological advice should be sought
  • Avoid diathermy if possible, otherwise consider bipolar
  • If monopolar is used, plate should be positioned so current flows away from pacemaker, short bursts only, and stop diathermy if arrhythmia occurs

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