Prospective, randomized comparison of electromyographic neuromuscular responses from the adductor pollicis and abductor digiti minimi muscles during rocuronium-induced neuromuscular block

BACKGROUND: Many clinicians monitor the abductor digiti minimi (ADM) muscle during surgery using electromyography (EMG) for ease and consistency of electrode placement, while practice guidelines recommend monitoring of responses at the adductor pollicis (AP) muscle. We compared the onset time of rocuronium neuromuscular block and the sugammadex-induced recovery time recorded simultaneously from the AP and ADM muscles. METHODS: In 44 consenting patients undergoing general anesthesia, simultaneous EMG recording of ADM and AP muscles was performed. Right- and left-hand selection of monitored muscle (AP vs. ADM) was randomized, and patients' handedness was recorded. The primary outcomes were the onset time of neuromuscular block (administration of rocuronium until train-of-four (TOF) count =0); recovery time (time from sugammadex administration until TOF ratio ≥0.9); and time to maximal recovery (sugammadex administration until TOF ratio=1.0). RESULTS: There were no significant differences between ADM and AP measurements in onset time, recovery to TOF ratio ≥0.9, or time to maximal recovery (TOF ratio=1.0) between EMG responses recorded simultaneously from ADM and AP muscles. However, a difference in recovery times between ADM and AP existed, depending on which hand was monitored. When ADM was monitored on the right hand, the readings showed earlier recovery than AP, and the mean difference was 93 s (25% faster) and 105 s (20% faster) for time to TOF ratio ≥0.9 and time to TOF ratio=1.0, respectively. We found no difference between the AP and ADM muscles when monitoring was performed on the left hand. CONCLUSIONS: The present study underscores the equivalency between ADM and AP muscles for routine neuromuscular monitoring during surgery. When monitoring the non-dominant arm, the ADM and AP muscles have similar recoveries. In the dominant arm, the ADM muscle recovery is significantly faster than that of the AP muscle.