title: Determination of the minimum alveolar concentration of isoflurane that blunts adrenergic responses in sheep and evaluation of the effects of fentanyl.
abstract: OBJECTIVE
  To determine the minimum alveolar concentration that blunts adrenergic responses (MACBAR) for isoflurane and evaluate effects of fentanyl on isoflurane MACBAR in sheep. ANIMALS 13 healthy adult Dorset-cross adult ewes.
  
  
  METHODS
  In a crossover design, each ewe was anesthetized 2 times for determination of isoflurane MACBAR. Anesthesia was induced with propofol administered IV. Sheep initially received fentanyl (5 μg/kg, IV, followed by a constant rate infusion of 5 μg/kg/h) or an equivalent volume of saline (0.9% NaCl) solution (control treatment). After a washout period of at least 8 days, the other treatment was administered. For MACBAR determination, a mechanical nociceptive stimulus (ie, sponge forceps) was applied at the coronary band for 1 minute. The MACBAR values of the 2 treatments were compared by means of a paired t test. During MACBAR determination, blood samples were collected for measurement of plasma fentanyl concentration.
  
  
  RESULTS
  Mean ± SD isoflurane MACBAR of the fentanyl and control treatments was 1.70 ± 0.28% and 1.79 ± 0.35%, respectively; no significant difference was found between the 2 treatments. Plasma concentration of fentanyl reached a median steady-state concentration of 1.69 ng/mL (interquartile range [25th to 75th percentile], 1.47 to 1.79 ng/mL), which was maintained throughout the study.
  
  
  CONCLUSIONS
  Administration of fentanyl at 5 μg/kg, IV, followed by a constant rate infusion of the drug at 5 μg/kg/h did not decrease isoflurane MACBAR. Further studies to determine the effect of higher doses of fentanyl on inhalation anesthetic agents and their potential adverse effects are warranted.
authors.forename: Michele
authors.initials: M
authors.lastname: Barletta
authors.forename: Stephanie A
authors.initials: SA
authors.lastname: Kleine
authors.forename: Erik H
authors.initials: EH
authors.lastname: Hofmeister
authors.forename: Merrilee
authors.initials: M
authors.lastname: Thoresen
authors.forename: John F
authors.initials: JF
authors.lastname: Peroni
authors.forename: Heather K
authors.initials: HK
authors.lastname: Knych
authors.forename: Alexandra M
authors.initials: AM
authors.lastname: Scharf
authors.forename: Jane E
authors.initials: JE
authors.lastname: Quandt
mesh_terms: D018663:Adrenergic Agents; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology; D000818:Animals; D018592:Cross-Over Studies; D004347:Drug Interactions; D005260:Female; D005283:Fentanyl / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics* / Q000494:pharmacology; D007530:Isoflurane / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D015742:Propofol; D012756:Sheep
chemical_list: D018663:Adrenergic Agents; D018685:Anesthetics, Inhalation; D007530:Isoflurane; D005283:Fentanyl; D015742:Propofol