Vagal nerve monitoring in surgery of the skull base: a comparison of efficacy of three techniques.

Objective: To compare three techniques of monitoring the vagal nerve during skull base surgery using laryngeal electromyography (EMG). Study Design: Prospective comparison. Setting: California Ear Institute at Stanford, tertiary referral center. Patients: Seventeen consecutive patients undergoing lateral skull base surgery potentially placing the vagal nerve at risk. Interventions: Each patient was simultaneously monitored intraoperatively with three separate EMG techniques: 1) endolaryngeal surface electrodes mounted on an endotracheal tube (ETT) (Xomed Surgical Products, Inc., Jacksonville, FL); 2) endoscopically placed endolaryngeal thyroarytenoid intramuscular hookwire electrodes; and 3) percutaneously placed cricothyroid intramuscular hookwire electrodes. Main Outcome Measures: Sensitivity, reliability, response magnitude, incidence of false-positive responses, and complications were recorded. Preoperative and postoperative vagal nerve function was noted. Results: The study was completed in 13 patients. The endolaryngeal intramuscular electrode technique responded at the lowest current stimulus (mean, 0.073 mA) with the highest average magnitude response. It responded in 100% of patients. The percutaneous intramuscular technique was similarly sensitive (mean stimulus, 0.089 mA) with a large average magnitude response but was much less reliable (responded in 69.2% of patients). The Xomed ETT was less sensitive (mean stimulus, 0.120 mA), had the lowest average magnitude response, and demonstrated medium reliability (responded in 76.9% of patients). The ETT exhibited the lowest incidence of spontaneous false-positive EMG activity. No complications were noted, and vagal nerve function was not compromised in any patient. Conclusions: Although the Xomed ETT exhibited ease of placement and a low false-positive response rate, it demonstrated lowest sensitivity compared with electrodes placed intramuscularly. The percutaneous intramuscular electrode technique was the least reliable, likely related to blind insertion, making it a less-desirable technique. Because of its highest relative sensitivity and reliability, the endolaryngeal intramuscular electrode technique of vagal monitoring is best supported by this study.