ABSTRACT
What are the basic principles of diathermy?
Diathermy devices are surgical instruments used to cut tissues and coagulate blood vessels.
They use the heating effect of high frequency AC (0.5–1.0 MHz) passing through tissues of high impedance to burn or vaporise tissues in contact with the diathermy instrument.
The heating effect of a current depends on the current density and duration.
In diathermy the current density at the point where the instrument makes contact with the tissue is very high.
In ‘cutting’ mode the current flows in an alternating sine wave pattern while in ‘coagulation’ mode the current flows in a pulsed sine wave pattern.
Diathermy devices can either be monopolar or bipolar.
In monopolar diathermy, current flows through a probe (active electrode) at a high current density and then returns via a diathermy plate (neutral plate) at low current density. The overall power that can be delivered is in the region of 100–400 W.
In bipolar diathermy, the current is passed between two probes within a modified pair of forceps. One probe delivers the current and the second acts as the return circuit so tissues between the probes are exposed to the current and heated. This system helps keep the electrical field focal. The overall power this system can generate is approximately 40 W.
