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 preserv ation of function. Electrically evoked facial nerve monitoring was com pared with ulnar train-of-four monitoring under progressive neuromuscu lar blockade. Using a rabbit model, the facial nerve function of six c ontrols was compared to that of six specimens with acute or chronic in juries. Eight of 18 patients who had undergone CPA tumor resection dur ing one year were also studied. Regression analysis correlated between ulnar nerve monitoring and facial electromyographic (EMG) peak voltag e in all groups. Facial EMG was measurable, even with 75 percent recep tor blockade. The results of this study support the hypothesis that hi gh degrees of neuromuscular blockade do not preclude satisfactory EMG monitoring of the facial nerve during CPA tumor surgery. This study di d 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 cir cumstances.