Fentanyl, Clonidine, and Repeated Increases in Desflurane Concentration, but Not Nitrous Oxide or Esmolol, Block the Transient Mydriasis Caused by Rapid Increases in Desflurane Concentration

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Abstract
Initial, but not subsequent, inhalation of 8% desflurane produces transient sympathetic stimulation.We hypothesized that initial but not subsequent increases should produce pupil dilation, and that N2 O, fentanyl, and clonidine, but not esmolol, should blunt the response. In 10 volunteers, we maintained anesthesia with 4% end-tidal desflurane in oxygen for 32 min, then increased the concentration to 8% for 10 min. In nine of the volunteers, we twice repeated the increase to 8%, separating each increase by a 32-min period at 4%. On separate days, five volunteers received 4%-8% desflurane in 60% N2 O; five received fentanyl 1.5 micro gram/kg or 4.5 micro gram/kg intravenously 5 min before 4%-8% desflurane; four received clonidine 4.3 micro gram/kg, orally, 90 min before 4% to 8%; and four received esmolol 0.75 mg/kg, intravenously, 1.5 min before 4%-8%. Without other drugs present, 4%-8% desflurane transiently increased pupil diameter to 5.4 +/- 0.5 mm (mean +/- SD), with subsequent 4%-8% increases producing attenuated responses (2.9 +/- 1.5 and 3.2 +/- 1.8 mm). N2 O produced a higher peak (6.2 +/- 0.7 mm). Fentanyl 1.5 micro gram/kg and 4.5 micro gram/kg decreased peak diameter (2.3 +/- 0.9 and 1.6 +/- 0.3 mm), as did clonidine (2.3 +/- 1.7 mm) but not esmolol. We conclude that, concurrent with sympathetic stimulation, an initial rapid increase in desflurane concentration transiently increases pupil diameter, whereas repeated increases produce attenuated responses. N2 O augments, fentanyl and clonidine attenuate, and esmolol does not affect the response. (Anesth Analg 1995;81:372-8)