Blend mode reduces unintended thermal injury by laparoscopic monopolar instruments: a randomized controlled trial

Background The purpose of this study was to compare histologic evidence of thermal injury at the epigastric and umbilical incisions after elective laparoscopic cholecystectomy performed using the monopolar “Bovie” instrument set on the higher voltage coag mode versus the lower voltage blend mode. We hypothesized that the higher voltage coag mode would create more unintended thermal tissue injury at the epigastric trocar’s incision. Methods A prospective blinded randomized controlled trial of patients undergoing elective laparoscopic cholecystectomy was performed. Patients were randomized to have their operation performed with the monopolar instrument set at 30 W on either the coag mode or the blend mode. Immediately at the end of the operation, a biopsy sample of skin was obtained from the lower edge of the epigastric incision (through which the monopolar instrument was inserted) and the umbilical incision (through which the camera/telescope was inserted). The outcomes measured were histologic evidence of thermal injury at the epigastric and umbilical incisions (determined by a blinded pathologist). Results Forty patients were randomized (20 per group). Baseline demographics in the two groups were similar for age, gender, body mass index, preoperative diagnosis, operative time, and blood loss. Unintentional thermal injury was found at 20 % of epigastric incisions and 35 % of umbilical incisions in the total group. The incidence of thermal injury was higher after operations using the coag mode compared to the blend mode at both the epigastric (35 vs. 5 %; p = 0.044) and umbilical (55 vs. 15 %; p = 0.019) trocar incisions. Conclusions Radiofrequency energy from the monopolar Bovie instrument causes unintentional thermal injury to skin adjacent to the epigastric and umbilical trocar incisions. The incidence of thermal injury was reduced by using the lower voltage blend mode compared to the coag mode at both the epigastric and umbilical trocar incisions. Registration number: NCT016648060 ( www.clinicaltrials.gov ).