Recovery from rocuronium-induced neuromuscular block was longer in the larynx than in the pelvic limb of anesthetized dogs.

OBJECTIVE: To determine if neuromuscular monitoring at the pelvic limb accurately reflects neuromuscular function in the larynx after administration of rocuronium in anesthetized dogs.

STUDY DESIGN: Prospective experimental study.

ANIMALS: Six healthy Beagle dogs.

METHODS: Anesthesia was maintained in dogs with isoflurane and a continuous infusion of dexmedetomidine. Rocuronium (0.6 mg kg-1 ) was administered intravenously to induce neuromuscular block. Train-of-four (TOF) impulses were applied to the left recurrent laryngeal nerve (RLn) and the peroneal nerve (Pn). The evoked TOF ratio (TOFR; T4:T1) was measured with electromyography (EMG) simultaneously at the larynx and at the pelvic limb. Spontaneous recoveries of T1 to 25% (T125% ) and 75% (T175% ) of twitch height, and to TOFR of 0.70 and 0.90 (TOFR0.90 ) at each EMG site were compared.

RESULTS: Data from five dogs were analyzed. Times to T125% were similar at the pelvic limb and larynx when measured by EMG; time to T175% was slower at the larynx by 6±4 minutes (p=0.012). The larynx had a slower recovery to TOFR0.70 (41±13 minutes) and TOFR0.90 (45±13 minutes) than did the pelvic limb [29±8 minutes (p=0.011) and 33±9 minutes (p=0.003), respectively]. When the pelvic limb EMG returned to TOFR0.70 and TOFR0.90 , the larynx EMG TOFR0.70 and TOFR0.90 values were 0.32±0.12 (p=0.001) and 0.38±0.13 (p=0.001), respectively.

CONCLUSIONS AND CLINICAL RELEVANCE: After administration of rocuronium, neuromuscular function assessed by EMG recovered approximately 36% slower at the larynx than at the pelvic limb. The results in these dogs suggest that quantitative neuromuscular monitoring instrumented at a pelvic limb may be unable to exclude residual block at the larynx in anesthetized dogs.