Direct-current injury: electrochemical aspects

Direct-current injuries have occurred to anesthetized patients connected to battery-operated medical devices. This study was designed to document the effects of direct current applied to two electrodes on a tissue surrogate (round steak) at room temperature. Direct current from a 9 V source was applied to a pair of stainless steel electrodes (1.6 cm diameter) spaced 4.3 cm center-to-center. Current flowed for 5 min increments at the first electrode site, 10 min at the second, 15 min at the third, etc. until at the last site, the current flowed for 30 min. In all, 63 measurements were made with the pair of electrodes, which were changed if they became corroded. Lesion appearance, lesion size, pH and resistance were measured. It was found that the pH under the negative electrode became strongly alkaline (pH > 12) and acidic (pH < 5.0) under the positive electrode. The lesion under the negative electrode was red with a dark purplish ring that identified the electrode perimeter. The lesion under the positive electrode was more uniform and gray in appearance. The largest increase in lesion diameter occurred in the first 5 min. In all cases the resistance decreased with the passage of time. At the start of each experiment, both electrodes were shiny. At the end of each experiment the electrodes were different in appearance. The negative electrode retained its original shiny appearance but the positive electrode was pitted and dull in appearance, reflecting the different chemical reactions at each site. The lesions under the negative electrodes were more severe, indicating that alkali is more damaging than the acid environment that was produced electrolytically.