Acceleromyographic monitoring of neuromuscular block over the orbicularis oris muscle in anesthetized patients receiving vecuronium

Study ObjectiveTo evaluate the level of neuromuscular block acceleromyographically over the orbicularis oris muscle.DesignProspective, randomized, controlled study.SettingOperating room of a university-affiliated hospital.Patients36 adult, ASA physical status I and II women scheduled for mastectomy with air-oxygen-isoflurane-fentanyl anesthesia.InterventionsPatients were randomized to two groups. In the orbicularis oris group (n=18), the facial nerve was stimulated and movement of the orbicularis oris muscle was measured acceleromyographically. In the control group (n=18), adduction of the thumb was quantified mechanically.MeasurementsOnset and recovery of neuromuscular block caused by vecuronium 0.1 mg/kg were compared between the groups.Main ResultsTime to onset of neuromuscular block in the orbicularis oris group was significantly shorter than in the control group (176 ± 52 vs. 220 ± 34 sec, mean ± SD; P = 0.004). Times to return of the first, second, third, or fourth (T1, T2, T3, or T4) response of train-of four (TOF), and recovery of T1/control were comparable between the groups. Train-of-four ratio (T4/T1) in the orbicularis oris group was significantly higher than in the control group 50 to 120 minutes after vecuronium administration (P < 0.05).ConclusionDepth of neuromuscular block can be assessed acceleromyographically over the orbicularis oris muscle. Onset of neuromuscular block is quicker and recovery of TOF ratio is faster over the orbicularis oris muscle than at the thumb in patients receiving vecuronium.