Intraoperative Monitoring: Normative Range Associated With Normal Postoperative Glottic Function

Objectives/HypothesisDespite increasing use of intraoperative nerve monitoring (IONM), there is limited information on normative electrophysiologic electromyographic (EMG) parameters. The objective of this study was to define normative parameters of recurrent laryngeal nerve (RLN) intraoperative neuromonitoring during thyroid surgery associated with normal postoperative vocal cord function. Study DesignProspective data collection in a tertiary care center. MethodsQuantitative analysis of evoked waveform amplitude and threshold was performed on 125 patients with 167 nerves at risk. Values were displayed as a mean with 5th percentile and 95th percentiles (5th-95th). Postoperative vocal cord function in all patients was documented. ResultsAll patients had normal postoperative laryngeal function (group I-normal) except for two patients who had postoperative transient vocal cord paralysis (group II-abnormal/outlier). The final amplitude between 247 and 3607 V at the end of dissection/end of surgery was associated in all group I patients with a normal postoperative neural function. Final intraoperative amplitude measures for group II averaged just 97.5 V, significantly different than our normative ranges obtained for group I, and fell outside of the group I 5% to 95% percentile range (P=.016). Final amplitude adequately predicted postoperative RLN impaired function immediately after surgery. ConclusionsWe propose IONM EMG data criteria that predict normal postoperative vocal cord function monitoring and provide information about nerve functioning at the end of the operation, thereby allowing adaptation of the surgical strategy when a bilateral procedure is indicated to avoid bilateral nerve paralysis. Level of Evidence4 Laryngoscope, 123:3026-3031, 2013