Edward L Jones, MD, Thomas N Robinson, MD, Paul N Montero, MD, Henry R Govekar, MD, Greg V Stiegmann. University of Colorado School of Medicine, Aurora, CO
INTRODUCTION: Radiofrequency energy delivered by the monopolar “bovie” is used in virtually every laparoscopic operation. Electromagnetic coupling can occur between the active electrode and conductive laparoscopic instruments without direct contact by a phenomenon termed antenna coupling. The PURPOSE of this study was (1) to determine if, and to what extent, radiofrequency energy from the “bovie” couples to common laparoscopic instruments and (2) to describe practical steps a surgeon can take to minimize these potentially harmful effects.
METHODS: In a laparoscopic simulator, monopolar radiofrequency energy was delivered to a laparoscopic L-hook. The tip of either an unlit 10 mm camera or a 5 mm grasper was placed adjacent to, but not touching, bovine liver tissue. Thermal imaging quantified the change in tissue temperature nearest the tip of the camera or grasper that was never in contact with the active electrode immediately at the end of the 5 second activation. Variables tested included generator power setting, parallel bundling versus separation of the camera cord and monopolar cord, and 4cm versus 20cm separation between the tip of the active electrode and the tip of the camera or grasper. Temperature rise is reported as a mean +/- standard deviation in degrees Celsius.
RESULTS: A five second activation (30 watts, coagulation mode, 4 cm separation between active electrode tip and camera or grasper tip) increased tissue temperature adjacent to the grasper tip by 2.2+/-2.2 degrees Celsius (p=0.013) and the camera tip by 38.2+/-8.0 degrees Celsius (p<0.001). The camera tip created significantly higher temperatures than the grasper tip (p<0.001). Lowering the generator power setting from 30 to 15 Watts decreased the heat generated at the tip of the camera (38.2+/-8.0 versus 13.5+/-7.5; p<0.001). Complete separation of the camera and active electrode cords reduced the heat generated at the tip of the camera by more than half when compared to parallel bundling of the cords (38.2+/-8.0 versus 15.7+/-11.6; p<0.001). Increasing the distance between the tip of the active electrode and the tip of the camera from 4 cm to 20 cm marginally reduced the amount of heat generated at the tip of the camera (38.2+/-8.0 versus 31.1+/-11.1; p=0.047).
CONCLUSIONS: Commonly used laparoscopic instruments couple monopolar radiofrequency energy without direct contact with the active electrode. This coupling phenomenon results in significant heat transfer from a non-electrically active instrument tip to adjacent tissue. An unlit, laparoscopic camera tip couples energy and heats tissue more than fifteen-fold higher in comparison to a grasper. Practical steps to minimize the amount of heat generated at the camera tip include: reducing the generator power setting, avoidance of parallel bundling of the camera and “bovie” cords, and increasing the distance between the instrument tip and the active electrode tip. These practical findings can alter how surgeons safely use monopolar energy during laparoscopic operations.
Session Number: SS02 – Instrumentation / Ergonomics
Program Number: S006
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