Clinical overview
Electrosurgery is the most ubiquitous energy modality in the gynaecological theatre, used in almost every laparoscopy, hysteroscopy, laparotomy and vaginal procedure for cutting and haemostasis. Precisely because it is so routine, its hazards are under-appreciated: the same physics that lets us coagulate a pedicle can perforate a bowel out of the surgeon's field of view, burn the patient at a distant skin site, ignite an airway or alcohol-prep fire, or interfere with a cardiac implantable electronic device. Energy-related injury — particularly bowel and ureteric thermal injury at laparoscopy — is a recurrent theme in medicolegal claims and in surgical morbidity audits, and a substantial proportion of these injuries are not recognised at the time of operation. The registrar who understands why electrosurgery behaves as it does will avoid the errors that the surgeon who simply "presses the yellow pedal" cannot.
This is a "discuss issues related to electrical safety" objective, so the weight sits in Core knowledge (the physics and the failure mechanisms) and Management (the safe-use drills and what to do when something goes wrong). The discussion must be genuinely mechanistic: examiners expect you to explain capacitive coupling, the difference between cut and coagulation waveforms, why a "no return-electrode" alarm is a patient-safety event, and how monopolar and bipolar circuits differ — not merely to recite a list of rules. In the South African context the issues are sharpened by the mix of older and donated electrosurgical units in district and regional theatres, variable biomedical-engineering maintenance, the high prevalence of HIV (sharps and plume exposure matter for the whole team), and the reality that the registrar is often the most senior person in a level-1 or level-2 theatre at night. This chapter sits alongside Safe use of surgical instruments, MIS complication prevention, Pneumoperitoneum, Operative hysteroscopy and ERAS principles.
Core knowledge
Figure F4.1 — Electrosurgery is current, not cautery: the patient is part of the circuit, power density (small tip vs large pad) decides the tissue effect, waveform decides cut versus coagulation, and bipolar confines current to the tissue between the jaws.
The basic circuit and what electrosurgery actually does
Electrosurgery uses high-frequency alternating current (radiofrequency, classically in the hundreds of kilohertz to low megahertz range) to generate heat within tissue. The key conceptual point is that the patient is part of an electrical circuit: current flows from the generator, through the active electrode, through the patient's tissue, and back to the generator. Tissue has electrical resistance (impedance), and current passing through a resistance generates heat — this is the thermal effect that cuts and coagulates. The reason high frequency is used is the frequency-response of excitable tissue: ordinary low-frequency mains current (50 Hz in South Africa) depolarises nerve and cardiac muscle and causes electrocution, whereas radiofrequency current oscillates far too fast to depolarise membranes, so it produces heat without neuromuscular stimulation.
Do not confuse electrosurgery ("diathermy") with electrocautery. In true electrocautery a current heats a wire, and it is the hot wire that touches and burns the tissue — current never enters the patient. In electrosurgery the current itself passes through the patient and generates heat in the tissue. Almost everything in a modern gynaecology theatre (the "Bovie", LigaSure, bipolar forceps, the hysteroscopic resectoscope) is electrosurgery, not cautery.
The tissue effect depends on power density — current concentrated into a small area produces intense, localised heating; the same current spread over a large area barely warms tissue. This single principle explains both how we cut (tiny contact area at the electrode tip → very high power density → rapid vaporisation) and why the return electrode is safe (huge contact area → low power density → negligible warming).
Cut, coagulation and the waveform
The generator shapes the current into different waveforms, and the registrar should be able to explain the difference:
- Cut (pure cut): a continuous (undamped), relatively low-voltage sinusoidal waveform. Continuous energy delivery superheats intracellular water so quickly that cells explode (vaporisation), producing a clean cutting effect with little lateral thermal spread or coagulation.
- Coagulation: an interrupted (damped, "on" only a small fraction of the time), much higher-voltage waveform. The intermittent high-voltage bursts dehydrate and denature tissue rather than vaporising it, producing coagulation/desiccation and, with non-contact sparking, fulguration. The higher peak voltage of coag mode is exactly why it is the mode most associated with capacitive coupling and insulation-failure injuries.
- Blend: intermediate duty cycles giving simultaneous cutting with some haemostasis.
A common teaching trap: "cut" is lower voltage than "coag", and lateral thermal spread is a property of energy delivered over time, not of the mode name alone — prolonged "cutting" near the ureter is still dangerous.