Recurrent laryngeal nerve safety parameters of the Harmonic Focus during thyroid surgery: Porcine model using continuous monitoring

Objectives/Hypothesis The Harmonic Focus (HF) is one of the most popular energy-based devices. The aim of this study was to provide recurrent laryngeal nerve (RLN) functional data that define the safety parameters of the HF during thyroidectomy. Study Design Prospective porcine model using continuous electrophysiologic monitoring. Methods Ten piglets were used. At varying distances from the RLN, the HF was activated (activation study). The HF was also applied directly on the RLN after activation on sternocleidomastoid muscle for 10 seconds with different cooling times (cooling study). Results In the activation study, there was no adverse electromyography (EMG) event at more than 1 mm distance. In the cooling study, there was no adverse EMG event after a 10-second cooling period. When the HF was cooled on the sternocleidomastoid muscle, there was no adverse EMG event after 2 seconds cooling time. Conclusions The safe distance of the HF was 1 mm, and it should be cooled for more than 10 seconds or 2 seconds after cooling on muscle. The HF should be used in a standardized manner to avoid RLN injury.