title: Effect of fentanyl target-controlled infusions on isoflurane minimum anaesthetic concentration and cardiovascular function in red-tailed hawks (Buteo jamaicensis).
abstract: OBJECTIVE
  To determine the impact of three different target plasma concentrations of fentanyl on the minimum anaesthetic concentration (MAC) for isoflurane in the red-tailed hawk and the effects on the haemodynamic profile.
  
  
  METHODS
  Experimental study.
  
  
  METHODS
  Six healthy adult red-tailed hawks (Buteo jamaicensis) of unknown sex with body weights (mean ± SD) of 1.21 ± 0.15 kg.
  
  
  METHODS
  This study was undertaken in two phases. In the first phase anaesthesia was induced with isoflurane in oxygen via facemask and maintained with isoflurane delivered in oxygen via a Bain circuit. Following instrumentation baseline determination of the MAC for isoflurane was made for each animal using the bracketing method and a supramaximal electrical stimulus. End-tidal isoflurane concentration (E'Iso) was then set at 0.75 × MAC and after an appropriate equilibration period a bolus of fentanyl (20 μg kg(-1)) was administered intravenously (IV) in order to determine the pharmacokinetics of fentanyl in the isoflurane-anaesthetized red-tailed hawk. During the second phase anaesthesia was induced in a similar manner and E'Iso was set at 0.75 × MAC for each individual. Fentanyl was infused IV to achieve target plasma concentrations between 8 and 32 ng mL(-1). At each fentanyl plasma concentration, the MAC for isoflurane and cardiovascular variables were determined. Data were analyzed by use of repeated-measures anova.
  
  
  RESULTS
  Mean ± SD fentanyl plasma concentrations and isoflurane MACs were 0 ± 0, 8.51 ± 4, 14.85 ± 4.82 and 29.25 ± 11.52 ng mL(-1), and 2.05 ± 0.45%, 1.42 ± 0.53%, 1.14 ± 0.31% and 0.93 ± 0.32% for the target concentrations of 0, 8, 16 and 32 ng mL(-1), respectively. At these concentrations fentanyl significantly (p = 0.0016) decreased isoflurane MAC by 31%, 44% and 55%, respectively. Dose had no significant effect on heart rate, systolic, diastolic or mean arterial blood pressure.
  
  
  CONCLUSIONS
  Fentanyl produced a dose-related decrease of isoflurane MAC with minimal effects on measured cardiovascular parameters in red-tailed hawks.
authors.affiliation: Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, CA, USA.
authors.forename: Juan C
authors.initials: JC
authors.lastname: Pavez
authors.forename: Michelle G
authors.initials: MG
authors.lastname: Hawkins
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Pascoe
authors.forename: Heather K DiMaio
authors.initials: HK
authors.lastname: Knych
authors.forename: Philip H
authors.initials: PH
authors.lastname: Kass
mesh_terms: D000759:Adjuvants, Anesthesia / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D000769:Anesthesia, Inhalation / Q000662:veterinary*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000187:drug effects*; D001831:Body Temperature / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule / Q000662:veterinary; D005283:Fentanyl / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D046428:Hawks / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects*; D007262:Infusions, Intravenous / Q000662:veterinary; D007530:Isoflurane / Q000008:administration & dosage / Q000494:pharmacology*; D009068:Movement / Q000187:drug effects
chemical_list: D000759:Adjuvants, Anesthesia; D018685:Anesthetics, Inhalation; D007530:Isoflurane; D005283:Fentanyl