Electrosurgery, Diathermy & Surgical Energy Devices

Both are forms of electrosurgery, which passes high-frequency alternating current through tissue to generate heat where the current density is high - cutting with a continuous waveform that vaporises cells, and coagulating with an interrupted waveform that desiccates and seals. The difference lies in the current path. In monopolar diathermy, current flows from a small active electrode through the patient to a large return, or dispersive, electrode; the current density is high at the small active tip, where the surgical effect occurs, and low at the large return pad, so the pad does not burn. In bipolar diathermy, the current passes only between the two tips of the forceps, so no return electrode is needed and no current passes through the rest of the patient. Monopolar is versatile, for both cutting and coagulation, but bipolar is safer near nerves, near or on implants, in patients with pacemakers, and in digits and other appendages with an end-arterial supply, although it only coagulates a small volume. The key safety issues are: correct application of the return electrode over well-perfused muscle near the site, and never cutting it down for a child, because reducing its area raises the current density and risks a burn; the risk of alternative-site burns from current diversion; pacemaker and defibrillator precautions, where I would prefer bipolar, use short bursts, position the return so the current path avoids the device, and involve the device team; the surgical-fire triad of oxidiser, fuel and ignition source, so I would let alcohol prep dry and manage oxygen; and surgical smoke, which is a respiratory hazard requiring evacuation. I would also remember that the harmonic scalpel is an ultrasonic device, not a form of bipolar cautery.