P15-F Intraoperative-neuromonitoring-recording effectiveness of the laryngeal-adductor-reflex (LAR) during thyroid surgery: Immediate and long-term EMG-ENT outcome correlation

Abstract

Background Intraoperative-neuromonitoring (IONM) of vocal cord function is of vital importance as part of the recurrent-laryngeal-nerve (RLN) monitoring during thyroid-parathyroid surgeries. The most popular IONM technique includes both vagus and RLN direct stimulation. We have substituted this method with the IONM-recording of the LAR and correlated its changes with immediate and long-term EMG-ENT outcome in a case series of 45 patients. Methods All patients underwent pre-postoperative direct laryngoscopy and thyroarytenoid EMG assessment (ENT within 24-h, EMG within 4-weeks after surgery). LAR was elicited by applying a single electrical stimulus on the laryngeal mucosa from surface-electrodes (ES) embedded in the endotracheal-tube (ETT) (duration 0.1–1 ms, intensity 6–8 mA, frequency 1 Hz), with the recording of cR1 and cR2 responses from the ES of the TET contralateral to the stimulus and ipsilateral to the surgical field. Significant changes in LAR amplitude responses were the critical parameters for IONM interpretation. Results From 45 patients (9-males; 36-females; age 28–81 years) 38 underwent bilateral thyroidectomy, and seven underwent hemithyroidectomy. All cR1 responses were elicited bilaterally at the onset of surgery. There was a reversible-temporary unilateral cR1 decrease-response in 6 cases, all presented with normal ENT-EMG postoperative result. A sustained unilateral cR1 drop-response occurred in 6 cases, all six showing ENT (paresis-paralysis) and EMG (sub-acute denervation) postoperative dysfunctions. At all times when cR1 amplitude dropping occurred, there was a temporal correlation with RLN direct surgical maneuvres. Conclusion There is a good correlation between LAR amplitudes changes during thyroid surgery with immediate and long-term EMG-ENT postoperative outcomes.