Evoked electromyography to rocuronium in orbicularis oris and gastrocnemius in facial nerve injury in rabbits.

Muscles innervated by the facial nerve show different sensitivities to muscle relaxants than muscles innervated by somatic nerves, especially in the presence of facial nerve injury. We compared the evoked electromyography (EEMG) response of orbicularis oris and gastrocnemius in with and without a non-depolarizing muscle relaxant in a rabbit model of graded facial nerve injury. Differences in EEMG response and inhibition by rocuronium were measured in the orbicularis oris and gastrocnemius muscles 7 to 42 d after different levels of facial nerve crush injuries in adult rabbits. Baseline EEMG of orbicularis oris was significantly smaller than those of the gastrocnemius. Gastrocnemius was more sensitive to rocuronium than the facial muscles (P < 0.05). Baseline EEMG and EEMG amplitude of orbicularis oris in the presence of rocuronium was negatively correlated with the magnitude of facial nerve injury but the sensitivity to rocuronium was not. No significant difference was found in the onset time and the recovery time of rocuronium among gastrocnemius and normal or damaged facial muscles. Muscles innervated by somatic nerves are more sensitive to rocuronium than those innervated by the facial nerve, but while facial nerve injury reduced EEMG responses, the sensitivity to rocuronium is not altered. Partial neuromuscular blockade may be a suitable technique for conducting anesthesia and surgery safely when EEMG monitoring is needed to preserve and protect the facial nerve. Additional caution should be used if there is a risk of preexisting facial nerve injury.