Abstract:
Neuromuscular blockade (NMB) is administered as part of a general anesthetic in order to keep the patient
immobilized during surgery and has been known to hinder intraoperative neuromonitorization. The aim of this study was
to determine the effects of different levels of NMB on electrical stimulation thresholds of the facial nerve during otologic
surgery.
Material and Methods—Intraoperative facial nerve monitorization was performed in 29 patients with advanced middle ear
disease. Electromyographic (EMG) responses were recorded by insertion of needle electrodes into the orbicularis oris and
orbicularis oculi muscles. Minimal facial nerve stimulations causing EMG responses in the facial musculature were
measured during full recovery from the effects of muscular relaxants and with 25%, 50%, 75% and 100% levels of NMB.
These defined NMB levels were maintained by the administration of a drip infusion of atracurium and were assessed
objectively by recording the hypothenar muscle action.
Results—All of the patients had detectable EMG responses of the facial musculature at the 50% and 75% levels of NMB
in response to the electrical stimulation of the facial nerve. The corresponding mean stimulation thresholds were
0.10 0.08 and 0.11 0.09 mA, respectively. No responses were measured in 31% of the patients when the level of
peripheral NMB was 100%.
Conclusion—This study suggests that a regulated 50% level of peripheral NMB provides reliable intraoperative EMG
monitoring of the facial musculature in response to electrical stimulation and adequate anesthesia, with full immobilization
of the patient.
