Electrical nerve and muscle stimulation by radio frequency surgery: role of direct current loops around the active electrode.

Tissue cutting by electrosurgery is often accompanied with stimulation of nerves and muscles, despite the high frequency of the alternating current being applied. The main source of this stimulation is thought to be the generation of low frequency current by the nonlinear sparking process. However, measurement of this low-frequency current, in the generator electrode's circuit, showed relatively small values, barely sufficient to support this hypothesis. In this study more powerful low frequency current could be identified, indeed also originating from the nonlinear sparking process. Local direct and low frequency currents, at a level of tens of milliamperes, appeared to be generated between different sites of the active electrode-tissue interface. Probably these local currents have not been noticed before as they cannot be detected in the outer chain of generator, electrodes, and connecting wires. This finding may explain why most measures, intended to prevent stimulation by modifying this outer chain, had only limited success.