Electromyographic monitoring of facial nerve under different levels of neuromuscular blockade during middle ear microsurgery

Abstract

Background The evoked electromyography (EMG) is frequently used to identify facial nerve in order to prevent its damage during surgeries. Partial neuromuscular blockade (NMB) has been suggested to favor EMG activity and insure patients’ safety. The aim of this study was to determine an adequate level of NMB correspondent to sensible facial nerve identification by evaluating the relationship between facial EMG responses and peripheral NMB levels during the middle ear surgeries. Methods Facial nerve evoked EMG and NMB monitoring were performed simultaneously in 40 patients who underwent tympanoplasty. Facial electromyographic responses were recorded by insertion of needle electrodes into the orbicularis oris and orbicularis oculi muscles after electrical stimulation on facial nerve. The NMB was observed objectively with the hypothenar muscle's twitching after electrical stimulation of ulnar nerve, and the intensity of blockade was adjusted at levels of 0, 25%, 50%, 75%, 90%, and 100% respectively with increased intravenous infusion of Rocuronium (muscle relaxant). Results All of the patients had detectable EMG responses at the levels of NMB ≤50%. Four out of forty patients had no EMG response at the levels of NMB ≥75%. A significant linear positive correlation was present between stimulation thresholds and NMB levels while a linear negative correlation was present between EMG amplitudes and NMB levels. Conclusions The facial nerve monitoring via facial electromyographic responses can be obtained when an intraoperative partial neuromuscular blockade is induced to provide an adequate immobilization of the patient. The 50% NMB should be considered as the choice of anesthetic management for facial nerve monitoring in otologic microsurgery based on the relationship of correlation.