Characterization and mitigation of stray radiofrequency currents during monopolar resectoscopic electrosurgery

Abstract

Study objective To determine patterns and range of stray radiofrequency (RF) currents flowing through the working element of monopolar resectoscopes during routine endometrial rollerball ablation or resection; and to determine whether straightforward modifications of the uterine resectoscope and the application of RF monitoring could provide a safe pathway for such currents. Design Prospective in vivo measurements (Canadian Task Force classification II-1). Setting University-affiliated teaching hospital. Patients Twelve women undergoing resectoscopic surgery. Interventions During routine resectoscopic surgery using 1.5% glycine irrigant solution, three modified 26F Storz resectoscope working elements (model 27070E) were adapted to be continuously monitored with an Encision AEM device for excessive capacitive coupling and other stray currents from insulation failure. Active electrodes used were 3 mm and 5 mm rollberballs and 8 mm–diameter cutting loops powered by ERBE or Valleylab generators at 120 W. Active and working element currents were monitored by Pearson current transformers followed by root-mean-squared detectors based on the Analog Devices AD-637 integrated circuit. Data were recorded using a Fluke 199C oscilloscope, then serially transferred to a notebook computer and analyzed using Flukeview, Excel, and Minitab software. Results Typical values of working element currents ranged from 0.10 to 0.20 A. Active electrode currents were typically in the range of 0.50 to 1.10 A. Frequently, the working element current exceeded the typical values and ranged up to 0.60 A. These current surges produced a heat factor (I 2t) of 0.45 A 2.sec in a 10-second period. Conclusions During resectoscopic electrosurgery, baseline, most likely capacitive coupled, currents were always present. In addition, high values of working element currents occurred frequently, and they surged up to 0.60 A for significant periods of time. Without the modification of the resectoscopic device, these currents have the capability of flowing through the patient’s genital tract and causing burns. Since monopolar electrosurgery remains an integral part of most hysteroscopic procedures, active electrode monitoring may offer a solution in protecting the patient and the surgeon from stray electrosurgical burns.