Intraoperative identification of laryngeal nerves with laryngeal electromyography

The laryngeal nerves are at risk during thyroid surgery, and several techniques have been described for their intraoperative identification to minimize potential damage. Nerve protection is based on the electromyographic recording from the muscles innervated by the laryngeal nerves, and that electrical activity is picked up by various techniques. We evaluated an electrode attachment to the endotracheal tube that provides a stable method for continuous recording of the laryngeal electromyogram. In addition, we tested various modalities of electrical stimulation in the region where the nerves are located, identified the most reliable evoked electromyographic activity, and characterized the wave form and latency. The results, obtained in 28 patients scheduled for thyroid and parathyroid surgery, indicate that the technique of recording from electrodes attached to the endotracheal tube is safe and reliable. Insulated bipolar forceps or a monopolar electrode was used to deliver low-voltage pulses (1 to 3 V) at 1 to 2 pulses/s generated by either battery-operated or optically isolated stimulators. The most unequivocal recordings were obtained with the monitoring equipment set to the nerve-conduction velocity modality, with the sweep set at 2 msec/cm. The technique clearly differentiated the evoked electromyographic responses obtained from the superior or recurrent laryngeal nerve and was easily performed with no perioperative complications.