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% (T1_25%) and 75% (T1_75%) of twitch height, and to TOFR of 0.70 and 0.90 (TOFR_0.90) at each EMG site were compared.

Results

Data from five dogs were analyzed. Times to T1_25% were similar at the pelvic limb and larynx when measured by EMG; time to T1_75% was slower at the larynx by 6 ± 4 minutes (p = 0.012). The larynx had a slower recovery to TOFR_0.70 (41 ± 13 minutes) and TOFR_0.90 (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 TOFR_0.70 and TOFR_0.90, the larynx EMG TOFR_0.70 and TOFR_0.90 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.