Discuss the principles of surgical diathermy, its safe use and the potential hazards

Diathermy is the use of an electrical current to cut tissue and coagulate blood via localised heating. Diathermy:

  • Uses high frequency, alternating current passing between two electrodes
    Frequencies between 300kHz and 2MHz are used, which have a negligible risk of inducing arrhythmia.
  • Heat energy produced is proportional to electrical power dissipated ()
  • Relies on the principle of current density
    • A high current density at the electrode causes tissue damage
    • A low current density (e.g. at the plate of a unipolar electrode) causes heating without damage

Diathermy Types

Diathermy can be either:

  • Unipolar
    Consists of a probe containing one electrode, and a large plate (placed elsewhere on the patient) containing the other probe.
  • Bipolar
    Consists of a pair of forceps with each point containing a separate electrode. Minimises the current passing between probes, and is used when using diathermy on electrically sensitive tissues (e.g. brain).

Diathermy Modes

Diathermy modes include:

  • Cutting
    Low-voltage mode producing a high current in the shape of a continuous sine wave.
  • Coagulate
    High-voltage mode producing a damped sine wave response.
  • Blended
    Mixture of cutting and coagulate on different tissues.


  • Burns
    From incorrectly applied unipolar plate.
  • Electrocution
    May injure patient, staff, or damage equipment and implants.
  • Electrical Interference
    May inhibit pacing in certain pacemakers, or trigger ICDs.
  • Smoke production
    Respiratory irritant, dissemination of viral particles, and may be carcinogenic.
  • Tissue dissemination
    Potential source of metastatic seeding.


  1. Aston D, Rivers A, Dharmadasa A. Equipment in Anaesthesia and Intensive Care: A complete guide for the FRCA. Scion Publishing Ltd. 2014.
Last updated 2017-09-16

results matching ""

    No results matching ""