title: Evaluation of the effect of alfentanil on the minimum alveolar concentration of halothane in horses.
abstract: The effect of 3 plasma concentrations of alfentanil on the minimum alveolar concentration (MAC) of halothane in horses was evaluated. Five healthy geldings were anesthetized on 3 occasions, using halothane in oxygen administered through a mask. After induction of anesthesia, horses were instrumented for measurement of blood pressure, airway pressure, and end-tidal halothane concentrations. Blood samples, for measurement of pH and blood gas tensions, were taken from the facial artery. Positive pressure ventilation was begun, maintaining PaCO2 at 49.1 +/- 3.3 mm of Hg and airway pressure at 20 +/- 2 cm of H2O. The MAC was determined in triplicate, using a supramaximal electrical stimulus of the oral mucous membranes. Alfentanil infusion was then begun, using a computer-driven infusion pump to achieve and maintain 1 of 3 plasma concentrations of alfentanil. Starting at 30 minutes after the beginning of the infusion, MAC was redetermined in duplicate. Mean +/- SD measured plasma alfentanil concentration during the infusions were 94.8 +/- 29.0, 170.7 +/- 29.2 and 390.9 +/- 107.4 ng/ml. Significant changes in MAC were not observed for any concentration of alfentanil. Blood pressure was increased by infusion of alfentanil and was dose-related, but heart rate did not change. Pharmacokinetic variables of alfentanil were determined after its infusion and were not significantly different among the 3 doses.
authors.affiliation: Department of Surgery, School of Veterinary Medicine, University of California, Davis 95616-8745.
authors.forename: P J
authors.initials: PJ
authors.lastname: Pascoe
authors.forename: E P
authors.initials: EP
authors.lastname: Steffey
authors.forename: W D
authors.initials: WD
authors.lastname: Black
authors.forename: J M
authors.initials: JM
authors.lastname: Claxton
authors.forename: J R
authors.initials: JR
authors.lastname: Jacobs
authors.forename: M J
authors.initials: MJ
authors.lastname: Woliner
mesh_terms: D015760:Alfentanil / Q000494:pharmacology*; D000768:Anesthesia, General / Q000379:methods / Q000662:veterinary*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004347:Drug Interactions; D006221:Halothane / Q000008:administration & dosage* / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D006736:Horses / Q000097:blood / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D008297:Male
chemical_list: D015760:Alfentanil; D006221:Halothane