The aim of this study was to stimulate the recurrent laryngeal nerve during thyroidectomy or parathyroidectomy and to record the muscle responses in an attempt to predict postoperative vocal fold mobility.

Intraoperative recurrent laryngeal nerve monitoring during general anaesthesia was performed by using an electrode-bearing endotracheal tube (nerve integrity monitor EMG endotracheal tube [Medtronic Xomed, Jacksonville, Flo, USA]). Two hundred and fifteen recurrent laryngeal nerves from 141 patients undergoing total thyroidectomy (n=74), hemithyroidectomy (n=63), or parathyroidectomy (n=4) were prospectively monitored. In each case, the muscle potential was recorded after stimulation of the recurrent laryngeal nerve by a monopolar probe.

The nerve stimulation threshold before and after dissection that induced a muscle response of at least 100μV ranged from 0.1 to 0.85mA (mean 0.4mA). The supramaximal stimulation intensity was defined as 1mA. The amplitude of muscle response varied considerably from one patient to another, but the similarity of the muscle response at supramaximal intensity between pre- and postdissection and between postdissection at the proximal and distal exposed portions of the nerve was correlated with normal postoperative vocal fold function. Inversely, alteration of the muscle response indicated a considerable risk of recurrent laryngeal nerve palsy, but was not predictive of whether or not this lesion would be permanent.

Recurrent laryngeal nerve monitoring with a system using surface electrodes is a simple, non-invasive technique that is just as sensitive as monitoring by intramuscular electrodes. Monitoring is helpful for initial nerve identification and is useful to determine nerve function during and after surgery, and to adapt the surgical strategy accordingly.