HF electrosurgery is the application of HF currents (in the frequency range of 300 kHz up to several MHz) to coagulate, fulgurate, spray coagulates or ablates tissue. Knowledge of how this and other physical modes interact with biological materials is becoming increasingly important to the surgeon for safe and consistent surgery.
Monopolar diathermy is used in endoscopic surgery for coagulation and for dissection (cutting). During monopolar diathermy current is conducted from the instrument through the tissues to a skin pad (neutral electrode) connected back to the generator. Heating occurs at sites of small cross section and low electrical conductivity. The instruments contact with the tissue has a small cross sectional area and the tissue is of relatively low conductivity (higher resistance or impedance) compared to the instrument material. A high current density occurs in the tissue in immediate contact with the instrument and heat is generated.
The effect of HF current on the tissues depends on:
· Temperature generated
· Shape and dimensions of the contact point (broader damage with broader contact)
· Time of activation (short bursts reduce depth and charring)
· Distance from the electrode
· Conductivity of the tissue (bleeding results in a change in conductivity)
· Power output from the generator (voltage)
· Amplitude and current wave form - time curve of the signal (cutting or coagulating settings)