Neuromuscular blocking drugs do not alter the pupillary light reflex of anesthetized humans

Objective: To test the hypothesis that systemically administered neuromuscular blocking drugs acutely alter resting pupil size or the direct reflex response to light in anesthetized humans. Design: Patients were randomized to receive an intravenous injection of saline (0.15 mL/kg), pancuronium bromide (0.1 mg/kg), or vecuronium bromide (0.15 mg/kg) after induction of general anesthesia and tracheal intubation. Setting: The University of California, San Francisco, Moffitt-Long Hospitals. Patients: Healthy adults (American Society of Anesthesiologists physical status I or II) of either sex scheduled for elective surgery requiring general anesthesia, tracheal intubation, and muscle relaxation of an anticipated duration of 2 or more hours. Main Outcome Measures: Measurements of resting pupil size, direct reflex response to light, and constriction velocity were obtained in double-blinded fashion using infrared pupillometry. Results: Pupillary size, reflex amplitude, and constriction velocity were not altered by the presence of either vecuronium or pancuronium. Tetanic stimuli and concomitant isoflurane administration respectively increased and decreased pupillary light reflex amplitude, indicating that pupillary responses were not fixed. Conclusion: We conclude that systemically administered neuromuscular blocking drugs (vecuronium and pancuronium) do not acutely affect the pupillary light reflex in healthy, anesthetized patients.