MONITORING THE ONSET OF NEUROMUSCULAR BLOCK AT THE ORBICULARIS OCULI CAN PREDICT GOOD INTUBATING CONDITIONS DURING ATRACURIUM-INDUCED NEUROMUSCULAR BLOCK

This study was designed to assess whether monitoring the orbicularis oculi (OO) can predict good tracheal intubating conditions. Fifty patients, ASA grade I or II were studied. Anesthesia was induced with thiopental (5 mg/kg) and fentanyl (3 mu g/kg). The ulnar and facial nerves were simultaneously stimulated using train-of-four (TOF) stimulations every 10 s. The responses of the adductor pollicis (AP) and the OO were estimated visually. Patients were randomly allocated to receive either atracurium 0.5 mg/kg (n = 30) or 0.3 mg/kg (n = 20). In each group, endotracheal intubation was performed randomly when the OO or the AP was completely blocked. if complete block was not obtained, intubation was performed 300 s after administration of atracurium. Intubating conditions were scored on a 1 to 4 scale. All intubations were performed by the same physician unaware of the dose and the muscular responses. After 0.5 mg/kg, both muscles were completely blocked in all patients. The average onset time (time from the injection of atracurium to the disappearance of all muscular responses after TOF) was shorter at the OO (2.35 +/- 0.12 min) than at the AP (3.59 +/- 0.15 min) (P < 0.001) (mean +/- SD). Endotracheal intubating conditions were comparable in both groups: good or excellent after 0.5 mg/kg. After 0.3 mg/kg, complete block was achieved only 2/20 at the OO and 12/20 at the AP. Intubating conditions were comparable in both groups: poor or inadequate, except in the two patients with complete OO block, for whom conditions were good. It is concluded that OO monitoring can predict good intubating conditions earlier than AP monitoring when using 0.5 mg/kg but not 0.3 mg/kg atracurium.