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Effect of dexmedetomidine, an alpha2-adrenoceptor agonist, on human pupillary reflexes during general anaesthesia
1Department of Anaesthesia and Perioperative Medicine, University of California, San Francisco 94143-0648, USA.
Aims:
To test the hypothesis that the alpha2-adrenergic agonist, dexmedetomidine, dilates the pupil and does not alter the pupillary light reflex of anaesthetized patients.
Methods:
Eight volunteers were administered general anaesthesia with propofol, nitrous oxide and alfentanil. One hour and 25 min after induction of anaesthesia, a 45 min infusion of dexmedetomidine was begun, targeting a plasma concentration of 0.6 ng x ml(-1). Pupil size, pupillary light reflex amplitude, light reflex recovery time, and reflex dilation were measured before and during dexmedetomidine infusion.
Results:
Dexmedetomidine produced no change in pupil size and light reflex recovery time, increased the light reflex from 0.30 +/- 0.14 to 0.37 +/- 0.12 mm and significantly reduced pupillary reflex dilation by 72 +/- 62%.
Conclusions:
These pupillary effects of dexmedetomidine in humans are difficult to reconcile with the findings obtained in cats and rats that have demonstrated a direct inhibitory effect of alpha2-adrenergic agonists on the pupilloconstrictor nucleus. The increase in the magnitude of the light reflex in response to dexmedetomidine does not necessarily involve an anxiolytic mechanism.