Effects of a single intravenous bolus of fentanyl on the minimum anesthetic concentration of isoflurane in chickens (Gallus gallus domesticus)

doi:10.1016/j.vaa.2016.07.006

Veterinary Anaesthesia and Analgesia

Volume 44, Issue 3, May 2017, Pages 546-554

https://doi.org/10.1016/j.vaa.2016.07.006 Get rights and content

Abstract

Objective

To assess the temporal effects of a single fentanyl intravenous (IV) bolus on the minimum anesthetic concentration (MAC) of isoflurane in chickens and to evaluate the effects of this combination on heart rate (HR) and rhythm, systemic arterial pressures (sAP) and ventilation.

Study design

Prospective experimental trial.

Animals

Seventeen adult chickens weighing 1.8 ± 0.2 kg.

Methods

Individual isoflurane MAC for 17 chickens was previously determined using the bracketing method. Chickens were anesthetized with isoflurane to evaluate the effects of a single IV fentanyl bolus (10 or 30 μg kg⁻¹) on isoflurane MAC over time using the up-and-down method. Ventilation was controlled. The isoflurane MAC reduction was estimated by logistic regression at 5 and 15 minutes after fentanyl administration. In the second phase, seven chickens were anesthetized with isoflurane, and fentanyl was administered (30 μg kg⁻¹) IV over 1 minute during spontaneous ventilation and HR and rhythm, sAP and ventilation variables were measured.

Results

At 5 minutes after IV administration of fentanyl (10 or 30 μg kg⁻¹), isoflurane MAC was significantly reduced by 17.6% (6.1–29.1%) [logistic regression estimate (95% Wald confidence interval)] and 42.6% (13.3–71.9%), respectively. Isoflurane MAC reduction at 15 minutes after IV administration of fentanyl (10 or 30 μg kg⁻¹) was 6.2% (−0.6 to 12.9%) and 13.2% (−0.9 to 27.3%), respectively; however, this reduction was not significant. No clinically significant cardiopulmonary changes or arrhythmias were detected after the administration of fentanyl (30 μg kg⁻¹).

Conclusions and clinical relevance

Administration of a single fentanyl bolus induced a dose-dependent and short-lasting reduction in isoflurane MAC. The higher dose induced no significant cardiopulmonary depression in isoflurane-anesthetized chickens during spontaneous ventilation. In chickens anesthetized with isoflurane, the clinical usefulness of a single fentanyl bolus is limited by its short duration of effect.

Introduction

Isoflurane is the most commonly used inhalation anesthetic agent in birds owing to its low blood–gas partition coefficient, which allows both rapid induction of, and recovery from, anesthesia and also because its elimination is not dependent on metabolic or excretory pathways (Ludders 2015). Concomitant administration of injectable and inhalation anesthetics may reduce the dose of inhalation agent required, resulting in not only less cardiopulmonary depression but also possible blunting of the sympathetic response to stimulation during surgery (Gunkel & Lafortune 2005).

Morphine decreased the minimum anesthetic concentration (MAC) of isoflurane by 52% in chickens (Concannon et al. 1995), and butorphanol reduced the isoflurane MAC in cockatoos by 25% (Curro et al. 1994). However, neither study evaluated the temporal effect of the opioid administration on isoflurane MAC. The duration of the anesthetic-sparing effect of opioids during inhalation anesthesia in birds is reported to be short. In the guineafowl, intravenous (IV) administration of butorphanol (4 mg kg⁻¹) reduced the sevoflurane MAC at 15 and 30 minutes by 21% and 11%, respectively (Escobar et al. 2012); however, this dosage was considered unsafe (Escobar et al. 2014). Intramuscular (IM) administration of morphine (3 or 6 mg kg⁻¹) in chickens reduced the isoflurane MAC at 15 minutes by 15% and 22%, respectively (Vela et al. 2014). Methadone (6 mg kg⁻¹) IM decreased isoflurane MAC by 30% at 15 minutes after administration in chickens; however, the effect was gone by 30 minutes (Escobar et al. 2016).

Fentanyl is a μ-opioid agonist with a short onset and duration of effect when administered as a single IV bolus (Kukanich & Wiese 2015). The results of a study of target-controlled infusions of fentanyl on isoflurane MAC in red-tailed hawks identified a plasma concentration-dependent reduction in MAC of up to 55% (Pavez et al. 2011). That study maintained constant plasma fentanyl concentrations; thus, the temporal effects of a bolus of fentanyl on isoflurane MAC were not examined.

The purpose of this study was to evaluate the temporal effects of an IV fentanyl bolus on isoflurane MAC in chickens and to measure selected cardiopulmonary variables. We hypothesized that a single bolus of fentanyl would induce a dose-dependent reduction in isoflurane MAC for a minimum of 15 minutes in chickens. We also hypothesized that the combination of fentanyl and isoflurane would not result in a greater cardiopulmonary depression when compared with an equipotent isoflurane concentration.

Section snippets

Material and methods

This study was approved by the Institutional Animal Care and Use Committee of the School of Agricultural and Veterinarian Sciences, São Paulo State University (no. 008078/13).

First phase

Individual isoflurane MAC was determined in three of the four birds in which it had not previously been determined. Mean ± SD isoflurane MAC for the three birds was 1.1 ± 0.1%. The fourth bird simultaneously extubated itself and regurgitated and aspirated gastric content during MAC determination, resulting in death. No adverse effects were noted during and after fentanyl administration. At 5 and 15 minutes after fentanyl (10 μg kg⁻¹) administration, isoflurane MAC was reduced by 17.6% (6.1–29.1%)

Discussion

The present study reports that the administration of a fentanyl bolus dose-dependently reduces the isoflurane MAC in chickens for <15 minutes. The higher dose tested reduced isoflurane MAC by 43%, which was similar to another study involving red-tailed hawks, in which isoflurane MAC reduction ranged from 31% to 55% after fentanyl target-controlled infusions (Pavez et al. 2011). However, neither dose of fentanyl studied caused significant reduction in isoflurane MAC at 15 minutes after

Acknowledgements

The authors thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for funding this study (no. 475127/2012-9) and thank Nathan da Rocha Neves Cruz and Camila Angelica Gonçalves for helping with the study development.

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Research paperEffects of a single intravenous bolus of fentanyl on the minimum anesthetic concentration of isoflurane in chickens (Gallus gallus domesticus)

Abstract

Objective

Study design

Animals

Methods

Results

Conclusions and clinical relevance

Introduction

Section snippets

Material and methods

First phase

Discussion

Acknowledgements

Vet Anaesth Analg

Seminars Avian Exot Pet Med

Br J Anaesth

Vet Anaesth Analg

Vet Anaesth Analg

Influence of a mu- and kappa-opioid agonist on isoflurane minimal anesthetic concentration in chickens

Am J Vet Res

Determination of the ED50 of isoflurane and evaluation of the isoflurane-sparing effect of butorphanol in cockatoos (Cacatua spp.)

Vet Surg

Fentanyl augments the blockade of the sympathetic response to incision (MAC-BAR) produced by desflurane and isoflurane: desflurane and isoflurane MAC-BAR without and with fentanyl

Anesthesiology

Gas-blood PCO2 gradients during avian gas exchange

J Appl Physiol

Research paper
Effects of a single intravenous bolus of fentanyl on the minimum anesthetic concentration of isoflurane in chickens (Gallus gallus domesticus)

Gas-blood PCO₂ gradients during avian gas exchange