Influence of Nondepolarizing Muscle Relaxants on Intraoperative Neuromonitoring during Thyroid Surgery

Objective: The objective of this study was to find a nondepolarizing muscle relaxant to replace succinylcholine during thyroid surgery with intraoperative neuromonitoring (IONM) because succinylcholine can cause severe adverse effects. Design: Prospective study of 232 patients undergoing thyroidectomies. Setting: A tertiary medical centre. Methods: One hundred thirty-one patients received 0.5 mg/kg rocuronium(group R) and 101 patients received 0.5 mg/kg atracurium (group A) to facilitate electromyographic (EMG) endotracheal tube insertion. EMG signals were obtained from the vagus nerve before and after dissection of the recurrent laryngeal nerve and were defined as the V-1 and the V-2 signal, respectively. Accelerometry (twitch [% TW]) was used to monitor the quantitative degree of neuromuscular transmission at the adductor pollicis muscle. Main Outcome Measures: The amplitude (mu V) of the V-1 and V-2 signals and the correlated degree of neuromuscular transmission (% TW). Results: V-1 and V-2 signals were obtained from all patients successfully. The % TW at the V-1 signal was significantly lower than that at the V-2 signal in group R and group A. The mean recovery time from complete neuromuscular blockade to the initial twitch was 43.9 +/- 6 11 minutes. Only in the subgroup in which the correlated TW was 0% while eliciting the V-1 signal were the amplitudes of the V-1 signals significantly lower than those of the V-2 signal in both groups. Conclusions: A single dose (0.5 mg/kg) of rocuronium and atracurium was feasible for IONM during thyroid surgery. This study showed that 44 minutes after administration of these two muscle relaxants is adequate for eliciting an EMG signal from the vagus nerve.