Recurrent Laryngeal Nerve Monitoring during Thyroid Surgery: Normative Vagal and Recurrent Laryngeal Nerve Electrophysiological Data

Objective Injury to the recurrent laryngeal nerve (RLN) remains a significant cause of morbidity during thyroid surgery. Intraoperative nerve monitoring (IONM) is being applied in many centers to facilitate nerve identification. The aim of this study was to elucidate normative human vagal and recurrent laryngeal nerve electromyograhic (EMG) parameters during standard IONM application. Study Design A prospective IONM study conducted over an 8-month period. Internal review board (IRB) approval was obtained. Settings Department of Otolaryngology, Division of Thyroid and Parathyroid Surgery, Massachusetts Eye and Ear Infirmary, Boston. Subjects and Methods All patients who were scheduled for routine thyroid, parathyroid, or neck exploration surgery were invited to participate. All patients had a preoperative and postoperative laryngeal examination to assess vocal cord function. Any patient with an abnormal preoperative laryngeal examination was excluded. Results Fifty-eight patients participated in this study. The right and left RLN latencies were similar. The left vagus latency was greater than the right vagus but was not significant. The RLN latency was significantly less than the vagus nerve. The right vagus nerve amplitude was significantly greater than the left. There was no difference between male and female amplitudes for either the RLN or vagus nerve. Conclusion This study highlights the electrophysiological/EMG differences and similarities between the RLN and vagus nerve. Normative amplitude measurements for bilateral RLN and vagus nerve stimulation are presented. There are limited data available in the literature on normal RLN and vagal EMG signals generated during thyroid surgery.