Predictive Value of Intraoperative Facial Motor Evoked Potentials in Vestibular Schwannoma Surgery Under 2 Anesthesia Protocols.

Abstract

We sought to validate the feasibility of facial motor evoked potential (FMEP) in facial nerve (FN) monitoring during vestibular schwannoma (VS) surgery under 2 anesthesia protocols and to examine its value for postoperative prognosis. This prospective study included 106 patients with VS who underwent microsurgical excision between May 2014 and November 2016 at the Beijing Tiantan Hospital, Capital Medical University, China. All patients were investigated for FMEP elicited by transcranial electrical stimulation in the contralateral facial motor cortex. The patients randomly received total intravenous anesthesia or combined intravenous-inhalation anesthesia. Postoperative FN function was evaluated 7-10 days after surgery (short-term) and at the last follow-up (long-term) using the House-Brackmann (HB) grading system. HB grades 1 and 2 were deemed satisfactory, whereas HB grades 3-6 were deemed unsatisfactory. The value of the final-to-start FMEP ratio for predicting short-term and long-term postoperative FN functions was examined. Valid FMEPs were obtained in 97 patients, which were recorded from the mentalis muscle. The FMEP amplitude ratio was significantly correlated with short-term and long-term postoperative FN functions. Receiver operating characteristic curve analysis showed that the FMEP ratio cut-off values of 77.4% (area under the curve= 0.797) and 56.9% (area under the curve= 0.900) predicted satisfactory FN function 7-10 days after surgery and at the last follow-up, respectively. No statistically significant difference was found in FMEP quantitative parameters between the 2 anesthesia protocols. The FMEP amplitude ratio is a valuable predictor for postoperative FN function. FMEP ratio ≥57% is predictive of satisfactory long-term FN function.