title: The pupillary light reflex. Effects of anesthetics and hyperthermia.
abstract: BACKGROUND
  The pupillary light reflex often is evaluated in the perianesthetic period to assess drug effects and brainstem function. Mild hypothermia alone or combined with isoflurane does not impair pupillary responses. Although perioperative hyperthermia is less common than hypothermia, abnormal increases in core temperature remain an important thermal disturbance. Accordingly, the pupillary effects of hyperthermia alone and hyperthermia combined with isoflurane and enflurane were evaluated. Additionally, the effects of nitrous oxide on pupillary responses were determined.
  
  
  METHODS
  The pupillary light reflex was evaluated in 31 non-surgical volunteers participating in concurrent thermoregulatory studies. Pupillary reflexes were quantified using a portable infrared pupillometer during (1) hyperthermia alone (n = 9), (2) hyperthermia with 0.8% and 1.2% end-tidal isoflurane (n = 8), (3) hyperthermia with 1.7% end-tidal enflurane (n = 5), and (4) inhalation of 60% N2O (n = 9).
  
  
  RESULTS
  Mild hyperthermia alone (core temperature 38.5 +/- 0.3 degrees C) produced no clinically significant change in the pupillary light reflex. Pupillary responses were decreased markedly with 0.8% isoflurane, 1.2% isoflurane, and 1.7% enflurane when the volunteers were normothermic. Mild hyperthermia combined with isoflurane or enflurane dilated the pupil and increased the amplitude of the light reflex. Sixty-percent nitrous oxide decreased the pupillary reflex only 26 +/- 4%.
  
  
  CONCLUSIONS
  Anesthetic-induced inhibition of the pupillary response to light is reversed partially by core hyperthermia. In contrast to enflurane and isoflurane, 60% N2O has little effect on the pupil.
authors.affiliation: Department of Anesthesia, University of California, San Francisco 94143-0648.
authors.forename: K G
authors.initials: KG
authors.lastname: Belani
authors.forename: D I
authors.initials: DI
authors.lastname: Sessler
authors.forename: M D
authors.initials: MD
authors.lastname: Larson
authors.forename: M A
authors.initials: MA
authors.lastname: Lopez
authors.forename: D E
authors.initials: DE
authors.lastname: Washington
authors.forename: M
authors.initials: M
authors.lastname: Ozaki
authors.forename: J
authors.initials: J
authors.lastname: McGuire
authors.forename: B
authors.initials: B
authors.lastname: Merrifield
authors.forename: M
authors.initials: M
authors.lastname: Schroeder
mesh_terms: D000328:Adult; D000777:Anesthetics / Q000494:pharmacology*; D005260:Female; D005334:Fever / Q000503:physiopathology*; D006801:Humans; D007530:Isoflurane / Q000494:pharmacology; D008027:Light; D008297:Male; D009609:Nitrous Oxide / Q000494:pharmacology; D011680:Pupil / Q000187:drug effects; D012025:Reflex, Pupillary / Q000187:drug effects* / Q000502:physiology
chemical_list: D000777:Anesthetics; D007530:Isoflurane; D009609:Nitrous Oxide