Determination of the minimum alveolar concentration of isoflurane that blunts adrenergic responses in sheep and evaluation of the effects of fentanyl

• Autores: Michele Barletta, Stephanie A. Kleine, Erik H. Hofmeister, Merrilee Thoresen, John F. Peroni, Heather K. Knych, Alexandra M. Scharf, Jane E. Quandt
• Localización: American Journal of Veterinary Research, ISSN-e 1943-5681, ISSN 0002-9645, Vol. 77, Nº. 2, 2016, págs. 119-126
• Idioma: inglés
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  • 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.

    PROCEDURES 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 AND CLINICAL RELEVANCE 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. (Am J Vet Res 2016;77:119–126)