Effect of neuromuscular blockade on facial nerve monitoring.

Direct facial nerve stimulation and monitoring during cerebellopontine angle (CPA) tumor surgery are critical for identification and preservation of function. Electrically evoked facial nerve monitoring was compared with ulnar train-of-four monitoring under progressive neuromuscular blockade. Using a rabbit model, the facial nerve function of six controls was compared to that of six specimens with acute or chronic injuries. Eight of 18 patients who had undergone CPA tumor resection during one year were also studied. Regression analysis correlated between ulnar nerve monitoring and facial electromyographic (EMG) peak voltage in all groups. Facial EMG was measurable, even with 75 percent receptor blockade. The results of this study support the hypothesis that high degrees of neuromuscular blockade do not preclude satisfactory EMG monitoring of the facial nerve during CPA tumor surgery. This study did demonstrate that chronically injured facial nerves may show greater sensitivity to the effects of neuromuscular blockade. Lower levels or avoidance of neuromuscular blockade should be employed under these circumstances.