Comparison of adductor pollicis and flexor hallucis brevis muscle electromyographic responses: a prospective cohort study.

Purpose: The use of a quantitative neuromuscular monitor is strongly recommended by many anesthesiology societies. While most monitors are used at the hand to record responses at the adductor pollicis muscle, this site may be unavailable. We sought to compare simultaneous quantitative neuromuscular measurements obtained at the adductor pollicis (hand) and flexor hallucis brevis (foot) muscles.

Methods: We preoperatively enrolled consenting patients in a prospective cohort study, and their attending anesthesiologists managed intraoperative neuromuscular block at their discretion. The anesthesiologists placed one set of electromyography electrodes over the ulnar nerve/adductor pollicis muscle and another over the posterior tibial nerve/flexor hallucis brevis muscle. During the onset of neuromuscular blockade, simultaneous measurements were obtained every 20 sec until the train-of-four (TOF) count reached 0. At the conclusion of the operation, sugammadex recovery data were recorded every 20 sec until a TOF ratio ≥ 0.9 was achieved.

Results: Of the 103 enrolled patients, 81 had simultaneous measurements during the onset of neuromuscular blockade at the hand and foot sites. The mean paired difference between the onset times at the two sites was 31 sec (95% confidence interval [CI], 5 to 56; P = 0.02). The mean paired difference between the offset times at the two sites was -3 sec (95% CI, -56 to 50; P = 0.26).

Conclusions: While quantitative neuromuscular monitoring at the flexor hallucis brevis (foot) muscle showed some statistical differences in onset time and a recovery compared with monitoring at the adductor pollicis muscle (hand), these differences are of unclear clinical significance.