Different behavior of electrosurgical currents between air and saline immersion therapeutic endoscopy

Impedance and voltage of monopolar currents are directly related. By replacing air with saline solution, a change in behavior of these currents are achieved in endoscopy, resulting in a desired coagulation effect. However, the underlying electrophysical mechanisms of this effect remain poorly explained. This investigation assessed the relationship between the electrical parameters and the surrounding environment for three high-voltage monopolar coagulation currents commonly used for therapeutic endoscopy. Six consecutive applications per setting and per environment were performed with dissection knife on porcine kidney. When transitioning from air to saline immersion, a 99% decrease in impedance was observed for all current settings tested (Air_Range: 4400-8150 Ω, Saline_Range: 64-71 Ω; p < 0.01 for all settings). This resulted in a 52-78% reduction in peak voltage (Air_Range: 920-1165 V, Saline_Range: 257-499 V; p < 0.01 for all settings), and a 237-2030% increase in power delivered (Air_Range: 3-19 W, Saline_Range: 50-117 W; p < 0.01 for all settings). The dramatic decrease in impedance results in a sharp reduction of voltage, explaining the coagulation effect observed when passing from air to saline-immersion therapeutic endoscopy.