Comparison of four facial muscles, orbicularis oculi, corrugator supercilii, masseter or mylohyoid, as best predictor of good conditions for intubation: A randomised blinded trial

CONTEXT Monitoring of facial muscles after neuromuscular blockade can give an early indication of respiratory muscle readiness for tracheal intubation. OBJECTIVE To assess which facial muscle, the orbicularis oculi, corrugator supercilii, masseter or the mylohyoid, is the best predictor of readiness for intubation after rocuronium. DESIGN Prospective, randomised, blinded trial. SETTING Single centre: Seoul, Korea, from August 2012 to November 2012. PATIENTS Two hundred and eighty-eight patients aged 22 to 64 years were randomised to one of eight study groups: orbicularis oculi, corrugator supercilii, masseter and mylohyoid for rocuronium 0.6 or 1.2mgkg^-1. INTERVENTION The maximum twitch depression at the eyelid (orbicularis oculi), the superciliary arch (corrugator supercilii), the cheek (masseter) and the submental triangle (mylohyoid) was assessed after rocuronium 0.6 and 1.2mgkg^-1. Endotracheal intubation was performed after maximal neuromuscular blockade, and intubating conditions were appraised. MAIN OUTCOME MEASURES The onset time of rocuronium and the quality of the intubation conditions were assessed. RESULTS The onset times in the orbicularis oculi, corrugator supercilii and masseter were significantly faster than that in the mylohyoid (P<0.001). 'Clinically acceptable' intubation conditions were significantly enhanced in the mylohyoid (94%) compared with those in the orbicularis oculi (80%) and masseter (78%) after rocuronium 0.6mgkg^-1 (P<0.05), and no difference with corrugator supercilii (92%). Despite differences in onset time of orbicularis oculi and masseter compared to mylohyoid (P<0.05), intubating conditions were similar among the four muscles after rocuronium 1.2mgkg^-1. CONCLUSION Following rocuronium 0.6 mgkg^-1 at similar depths of anaesthesia, the monitoring of the corrugator supercilii provided the best balance of a shorter onset time while maintaining 'clinically acceptable' intubation conditions. Trial registration: IRB File No.: HYUH 2012-07-009.