The orbicularis oculi and the adductor pollicis muscles as monitors of atracurium block of laryngeal muscles.

The aim of this study was to determine whether atracurium-induced neuromuscular block at the laryngeal adductor muscles could be predicted by visual inspection of either adductor pollicis or orbicularis oculi responses. Twenty-one ASA Class I or II patients were anesthetized with propofol (2-2.5 mg/kg) and fentanyl (2-5 micrograms/kg). Tracheal intubation was performed without neuromuscular blocking drugs. Patients were assigned randomly to receive atracurium 0.3 or 0.5 mg/kg intravenously. Train-of-four stimulation was applied to the ulnar, facial, and recurrent laryngeal nerves. Laryngeal response was measured as the pressure change in the tracheal tube cuff positioned between the vocal cords. The response at the adductor pollicis and orbicularis oculi was evaluated visually by two observers who detected if and when block was complete. Twelve patients, including all those receiving 0.5 mg/kg, had complete orbicularis oculi block. The same patients, except one, also had 100% laryngeal block. Adductor pollicis response was abolished in the same 12 patients plus an additional 4 patients. In patients receiving atracurium 0.5 mg/kg, laryngeal and orbicularis oculi responses were abolished faster (mean +/- SD: 132 +/- 80 and 146 +/- 58 s, respectively) than the adductor pollicis muscle (243 +/- 55 s; P < 0.05). There was a significant correlation (r = 0.94; P < 0.001) between neuromuscular block onset time at the laryngeal adductor and orbicularis oculi muscles but not between laryngeal and thumb muscles. The authors conclude that, after injection of atracurium, laryngeal adductor and orbicularis oculi blocks have similar intensities and time courses.(ABSTRACT TRUNCATED AT 250 WORDS)