Electromyographic Response of Facial Nerve Stimulation Under Partial Neuromuscular Blockade During Resection of Vestibular Schwannoma

Abstract

To evaluate whether use of partial nondepolarizing neuromuscular blocking agents, at a train-of-four level 1, compromise facial nerve monitoring during vestibular schwannoma (VS) resection. Sixty consecutive patients undergoing VS resection were enrolled into a partial peripheral neuromuscular blockade group or free of neuromuscular blockade group. Stimulation threshold to elicit an electromyographic response amplitude of at least 100 μV was recorded at the proximal and distal facial nerve after VS removal. The proximal-to-distal ratio of amplitude of the orbicularis oculi and oris muscles was calculated. All patients successfully passed the electromyography monitoring test. Mean electrical stimulation thresholds were higher in the peripheral neuromuscular blockade group than in the free of neuromuscular blockade group (0.12 mA vs. 0.06 mA at proximal site, P= 0.001; 0.08 mA vs. 0.03 mA at distal site, P= 0.0002). The differences in median proximal-to-distal amplitude ratios were not statistically significant in both groups. There was a trend toward more patients needing phenylephrine. Recovery profiles were comparable in the 2 groups. Although mean stimulation threshold to elicit a response amplitude was higher in the peripheral neuromuscular blockade group than in the free of neuromuscular blockade group at the proximal site, the stimulation thresholds in both groups were sufficient for facial nerve monitoring in VS surgery, indicating no clinical difference in both groups.