Electrosurgery: heating, sparking and electrical arcs

The translation of impedance (R), current (I), and voltage (V) into tissue effects and the understanding of the settings of electrosurgical units is not obvious if judged by the many questions during live surgery. Below 200 V, the current heats the tissue until the steam of boiling stops the current. Thus, slower heating, because of less energy or a larger contact area, results in deeper coagulation. Above 200 V and a duty cycle (per cent of time electricity is delivered) of >50% (yellow pedal), sparks become electric arcs, and the heat causes the explosion of superficial cells, i.e. cutting. With higher voltages, cutting is associated with coagulation, i.e. blended current. With even higher voltages and a duty cycle <10% preventing arching, only coagulation occurs (blue pedal; forced coagulation). Voltage being crucially important for tissue effects, newer electrosurgical units deliver a constant voltage and limit the energy output (Maximal Watts: W=I*V= joules/sec). Unfortunately, the electrosurgical units indicate the combination of voltage and duty cycles as a force of cutting (pure cutting or blended) or coagulation (soft, forced or spray) current. It is important that the surgeon understands whether electrosurgical units control voltages or output, as well as the electrical basics of the different settings and programs used.