The corrugator supercilii, not the orbicularis oculi, reflects rocuronium neuromuscular blockade at the laryngeal adductor muscles

Background: Some studies suggest that the orbicularis oculi is resistant to neuromuscular blocking drugs and behaves like laryngeal muscles. Others re port little or no difference between the orbicularis oculi and the adductor pollicis, These discrepancies could be related to the exact site of record ing. The purpose of this study was to compare two monitoring sites around t he eye with the adductor pollicis and the laryngeal adductor muscles, Methods: After institutional approval and informed consent, the evoked resp onse to train-of-four stimulation was measured In 12 patients by acceleromy ography at the thumb (adductor pollicis), the eyelid (orbicularis oculi), a nd the superciliary arch (corrugator supercilii) after 0.5 mg/kg rocuronium during propofol-fentanyl-nitrous oxide anesthesia. In 12 other patients, l aryngeal adductor neuromuscular blockade was assessed via the cuff of the t racheal tube and compared with the adductor pollicis and the corrugator sup ercilii after 0.6 mg/kg rocuronium, Results: After 0.5 mg/kg, maximum blockade (%T1, mean +/- SD) was less at t he corrugator supercilii (80 +/- 20%) than at the adductor pollicis (100 +/ - 1%) and the orbicularis oculi (93 +/- 8%) (P < 0.01). Clinical duration ( 25%T1) was shorter at the corrugator supercilii (12 +/- 7 min) than at the adductor pollicis (25 +/- 4 min) and orbicularis oculi (24 +/- 10 min) (P < 0.01). After 0.6 mg/kg, maximum blockade was similar at the corrugator sup ercilii (88 +/- 8%) and the laryngeal adductor muscles (89 +/- 11%). Clinic al duration at the corrugator supercilii and the laryngeal adductors was 17 +/- 7 and 17 +/- 10 min, respectively. Conclusions: Muscles around the eye vary in their response to rocuronium, T he response of the superciliary arch (corrugator supercilii) reflects block ade of laryngeal adductor muscles. However, the eyelid (orbicularis oculi) and thumb (adductor pollicis) have similar sensitivities.