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.