Intraoperative electromyographic assessment of recurrent laryngeal nerve stress and pharyngeal injury during anterior cervical spine surgery with Caspar instrumentation

Object. Recurrent laryngeal nerve (RLN) injury occurs after anterior cervic al spine procedures. In this study the authors used intraoperative electrom yographic (EMG) monitoring of the posterior pharynx as a surrogate for RLN function and monitored endotracheal tube (ET) cuff pressure to determine if there was an association between these variables and clinical outcome. Methods. Sixty patients in whom anterior cervical spine procedures were to be performed comprised the study population. After intubation, the ET cuff was adjusted to a just seal volume and attached to a pressure monitor. A la ryngeal surface electrode was placed in the posterior pharynx, and spontane ous EMG activity was monitored throughout the procedure. Cuff pressures and EMG activity were recorded during neck retraction and when EMG activity in creased 20% above baseline. Patients were divided into two groups: those wi th sore throat/dysphonia and those without symptoms. Cuff pressures and EMG values were compared between groups, and the differences were correlated w ith clinical outcome. Conclusions. Hoarseness immediately after surgery was reported in 38% of pa tients whereas 15% exhibited severe symptoms. In symptomatic patients the p eriod of intubation had been longer, and the ET cuff pressures had been ele vated. In most patients EMG activity increased during insertion of the retr actor and decreased after its removal. In these patients a greater number o f episodes of elevated EMG activity during surgery were also noted. Two pat ients experienced prolonged hoarseness, and one required teflon injections of the vocal fold. This patient's EMG activity increased (15-18 rimes basel ine) during surgery. In the few patients who were symptomatic with increase d EMG activity, neither the timing nor direction of change could be associa ted with symptoms. Intubation time and elevated ET cuff pressure were the m ost important contributors to dysphonia and sore throat after anterior cerv ical spine surgery.