Unintended Stray Energy from the Monopolar Instrument: Beware of the Dispersive Electrode Cord

Nicole T Townsend, MD1, Nicole Nadlonek, MD1, Edward L Jones, MD, MPH2, Gregory V Stiegmann, MD1, Thomas N Robinson, MD1. 1University of Colorado, 2Ohio State University

BACKGROUND: The monopolar instrument emits stray energy from the active electrode’s cord (via a phenomenon termed “antenna coupling”) which is implicated in unintended thermal injury in laparoscopy. Stray energy emitted from the dispersive electrode cord has not been studied. The PURPOSE of this study was to determine if, and to what extent, the dispersive electrode’s cord contributes to unintended radiofrequency energy transfer and to describe practical steps that can minimize the magnitude of antenna coupling from the dispersive electrode cord.

METHODS: In a laparoscopic simulator, a monopolar generator delivered radiofrequency energy to an L-hook. The tips of standard, non-electrical laparoscopic instruments (an unlit 10mm telescope or a 5mm grasper) were placed adjacent to bovine liver tissue and were never in contact with the active electrode. The active electrode cord was kept separate from other cords in the system unless specifically described. Thermal imaging quantified the change in tissue temperature nearest the tip of the non-electrical instrument following a 5 second activation of the active electrode set on 30 Watts coagulation mode (unless specified). The dispersive electrode’s cord was oriented in various positions relative to the other instruments and cords.

RESULTS: When orienting the dispersive electrode cord in parallel to the camera cord, the tissue temperature increased at the telescope tip by 46±6°C from baseline (p<0.001). Similar heat was generated at the telescope tip when the camera cord was oriented parallel to the dispersive versus active electrode cords. (46±6°C v. 48±7°C, p=0.48). The temperature change at the telescope tip was greater when the dispersive electrode cord was oriented in parallel to the camera cord compared to when the cords were separated (46±6°C v. 27±7°C, p<0.001). When the dispersive cords are in parallel, adding a second dispersive electrode decreases the temperature change (46±6°C v. 25±9°C, p<0.001). With the dispersive electrode cord oriented parallel to the camera cord, temperature increase was greater at the telescope tip with use of coagulation versus cut mode (33±7°C v. 22±6°C, p<0.001) and with prolonged activation time of 15 seconds versus 5 seconds (45±10°C v. 33±7°Cp<0.001).

CONCLUSIONS: Stray energy emitted from the dispersive electrode cord heats tissue >40°C via antenna coupling at the camera/telescope tip. Surprisingly, the magnitude of energy transfer is similar when comparing dispersive and active electrode cords. Practical steps to minimize stray energy transfer include avoiding orienting the dispersive electrode cord in parallel with other cords, adding a second dispersive electrode, using cut mode in preference to coagulation mode, and shortening dwell time. Understanding the potential for stray energy from the dispersive electrode cord will help surgeons to set-up their operating rooms to optimize electrosurgical safety and mitigate unintended thermal injury to patients.

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