Blend Mode Reduces Unintended Thermal Injury By Monopolar Instruments: A Randomized Controlled Trial

Edward L Jones, MD, Thomas N Robinson, MD, Paul N Montero, MD, Henry R Govekar, MD, Gregory V Stiegmann, MD

University of Colorado School of Medicine, Aurora, CO

INTRODUCTION: The monopolar “bovie” is used in virtually every laparoscopic operation. When active, the bovie emits radiofrequency energy that can cause unintended thermal injury to nearby structures without direct contact by capacitive and antenna coupling. The PURPOSE of this study was to compare histologic evidence of thermal injury at the epigastric and umbilical incisions following laparoscopic cholecystectomy performed using the higher voltage coag mode versus the lower voltage blend mode. We hypothesize that the higher voltage coag mode will create more unintended thermal tissue injury in comparison to the lower voltage blend mode.

METHODS AND PROCEDURES: We performed a prospective, blinded randomized controlled trial of patients undergoing elective laparoscopic cholecystectomy at a University hospital. Patients were randomized to have the operation performed with either the higher voltage coag mode or lower voltage blend mode delivered to the monopolar instrument. The generator was set at 30 Watts power for both groups. At the completion of the operation, skin was biopsied from the epigastric trocar incision (the incision through which the monopolar instrument was inserted) and the umbilical trocar incision (the incision through which the laparoscope was inserted). Thermal injury was determined by a blinded pathologist using both hematoxylin & eosin, and picro Sirius red stains. Statistical analysis was performed using two-sided Fisher’s exact test for categorical data and non-parametric t-test for continuous data.

RESULTS: Forty patients were randomized (twenty per group). Baseline demographic data in the two study groups (blend versus coag mode groups) were similar for age, gender, body mass index, operative time and blood loss. The incidence of thermal injury was higher for all skin biopsies obtained in the coag mode group in comparison to the blend mode group (45% versus 10%; p<0.001).

Incidence of Thermal Injury to Skin by Location

Blend Mode (Lower Voltage) n=20 Coag Mode (Higher Voltage) n=20 p
Epigastric Incision Skin Biopsy 5% (1) 35% (7) 0.044
Umbilical Incision Skin Biopsy 15% (3) 55% (11) 0.019
Total Thermal Injuries 10% (4) 45% (18) <0.001

CONCLUSION: Radiofrequency energy emitted from the monopolar “bovie” causes unintentional thermal injury to skin adjacent to the epigastric and umbilical trocar incisions. The incidence of thermal injury at both the umbilical and epigastric incisions was reduced by using the lower voltage blend mode in comparison to the higher voltage coag mode. In sum, unexplained laparoscopic complications may arise from unintentional thermal injury and can be reduced by using lower voltage energy modes during laparoscopic cholecystectomy.


Session: Podium Presentation

Program Number: S079

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