Effect of fentanyl target-controlled infusions on isoflurane minimum anaesthetic concentration and cardiovascular function in red-tailed hawks (Buteo jamaicensis)

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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. Study design Experimental study. Animal population Six healthy adult red-tailed hawks (Buteo jamaicensis) of unknown sex with body weights (mean±SD) of 1.21±0.15kg. 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 (20μgkg -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 32ngmL -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±11.52ngmL -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 32ngmL -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 and clinical relevance Fentanyl produced a dose-related decrease of isoflurane MAC with minimal effects on measured cardiovascular parameters in red-tailed hawks.

Original languageEnglish (US)
Pages (from-to)344-351
Number of pages8
JournalVeterinary Anaesthesia and Analgesia
Volume38
Issue number4
DOIs
StatePublished - Jul 2011

Keywords

  • Avian
  • Fentanyl
  • Isoflurane
  • MAC
  • Red-tailed hawk
  • Target-controlled infusion

ASJC Scopus subject areas

  • veterinary(all)

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