Train-of-four stimulation for adductor pollicis neuromuscular monitoring can be applied at the wrist or over the hand.

Adductor pollicis stimulation over the ulnar nerve at the wrist is the standard method of monitoring neuromuscular function. Stimulation over a muscle is believed to cause direct muscle contraction, but evidence for this is lacking. In this study we sought to determine whether direct muscle stimulation occurred during stimulation of the adductor pollicis in the hand and whether the responses were comparable to those observed with stimulation at the wrist. In 20 patients anesthetized with sevoflurane, 1 pair of stimulating electrodes was positioned over the ulnar nerve at the wrist. A second pair was placed between the first and second metacarpals on the palmar and dorsal aspects of the hand. The acceleromyographic response was monitored. Rocuronium 0.6 mg/kg was administered. Train-of-four (TOF) stimulations were applied at the wrist site until maximal blockade. Then, stimulation was applied to the hand site. During recovery, both sites were monitored alternately. After injection of rocuronium, 17 of 20 patients showed no twitch response at either site. One patient had a response at both stimulation sites, and two patients had responses only at the wrist site. With a Bland and Altman analysis, TOF ratios during recovery at the hand showed a bias of 0.5% and limits of agreement of +/-11.8% as compared with the wrist. Stimulation in the hand causes no direct muscle stimulation because the response is no more than that produced by stimulation at the wrist. Both sites yield comparable TOF ratios.