Diathermy
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.
Risks
- 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.
References
- Aston D, Rivers A, Dharmadasa A. Equipment in Anaesthesia and Intensive Care: A complete guide for the FRCA. Scion Publishing Ltd. 2014.