Intraoperative Electrophysiologic Monitoring of the Recurrent Laryngeal Nerve During Thyroid and Parathyroid Surgery: Experience With 1,381 Nerves at Risk

Objectives: The electrophysiologic responses of 1,381 recurrent laryngeal nerves (RLN) during monitored neck surgery were recorded and reviewed. Study Design: Retrospective case series. Methods: With institutional review board approval, we reviewed thyroid and other neck surgeries performed with intraoperative nerve monitoring (IONM) between the years 1995 and 2006. This list yielded consecutively monitored 1,381 RLNs, with over 3,000 hours of monitoring experience. All patients underwent preoperative and postoperative laryngoscopy. In an initial subset of patients, both hook-wire and endotracheal tube (ETT) surface electrodes were utilized. Normative stimulation parameters; postoperative vocal cord function prognostication using monitoring data; and false-positive, false-negative, and passive electrophysiologic responses were evaluated Results: Hook-wire electrodes and ETT surface electrodes were found to have good correlation in terms of amplitude (correlation coefficient, R = 0.89). Nerve stimulation of 1 to 2 mA resulted in an ipsilateral biphasic response, with 3.3 ms mean latency and 900 mu V mean amplitude. Permanent and temporary RLN paralysis rates were 0% and 0.7%, respectively. Specificity of electromyography (EMG) loss of signal (LOS) postoperative vocal cord paralysis (VCP) detection was 99.9%, and sensitivity was 33%. Negative predictive value of EMG LOS at the end of surgery in the prediction of postoperative VCP was 99.6%, whereas its positive predictive value for VCP was 75%. Conclusion: Intraoperative nerve monitoring of the RLN during thyroid and other neck surgeries can aid in the nerve mapping, nerve identification, and prognostication of postoperative vocal cord function, which in turn can influence the surgeon's decision to proceed to bilateral surgery.