TOF count at corrugator supercilii reflects abdominal muscles relaxation better than at adductor pollicis

Background: A recovery profile from neuromuscular block similar to thatof abdominal (AB) muscles, but different to that of the adductorpollicis (AP) muscle, has been demonstrated at the corrugatorsupercilii (CSC) muscle. We hypothesized that neuromusculartransmission (NMT) monitoring of CSC might provide useful informationon AB relaxation compared with AP. We compared the visual estimationof NMT at CSC and AP with electromyographic measurements ofAB during recovery from a vecuronium block. Methods: Ten adult patients were studied during balanced anaesthesia.After induction of anaesthesia and tracheal intubation withoutneuromuscular blocking agents, supramaximal stimulations wereapplied to three nerves: left 10th intercostal, ulnar, and facial.Electromyographic activity (EMG) of AB was measured (ABEMG).After a bolus dose of vecuronium 0.1 mg kg^–1, an independentobserver blinded to the EMG measurements counted visually detectabletrain-of-four (TOF) responses at CSC and AP. Values of ABEMGassociated with 1 to 4 TOF responses at CSC and AP were compared.Values are means (SD). Results: Reappearance of the first and second TOF responses at CSC occurredsignificantly (P < 0.05) earlier and at lower ABEMG recoverythan that of AP 35 (8) and 41 (9) min vs 51 (10) and 56 (12)min; and 17 (8) and 26 (9)% vs 56 (10) and 75 (11)%, respectively]. Conclusions: We demonstrated that the TOF response count at the CSC, comparedwith the AP, allowed a better quantification of the degree ofAB muscle relaxation during recovery from vecuronium block.