• Rachel C Hector, Marlis L Rezende, Khursheed R Mama, Eugene P Steffey, Heather K Knych, Ann M Hess, Juhana M Honkavaara, Marja R Raekallio, and Outi M Vainio.
• Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, USA.
• Vet Anaesth Analg. 2017 Jul 1; 44 (4): 755-765.

ObjectiveTo determine the effects of low and high dose infusions of dexmedetomidine and a peripheral α2-adrenoceptor antagonist, MK-467, on sevoflurane minimum alveolar concentration (MAC) in dogs.Study DesignCrossover experimental study.AnimalsSix healthy, adult Beagle dogs weighing 12.6±0.9 kg (mean±standard deviation).MethodsDogs were anesthetized with sevoflurane in oxygen. After a 60-minute instrumentation and equilibration period, the MAC of sevoflurane was determined in triplicate using the tail clamp technique. PaCO2 and temperature were maintained at 40±5 mmHg (5.3±0.7 kPa) and 38±0.5 ºC, respectively. After baseline MAC determination, dogs were administered two incremental loading and infusion doses of either dexmedetomidine (1.5 μg kg-1 then 1.5 μg kg-1 hour-1 and 4.5 μg kg-1 then 4.5 μg kg-1 hour-1) or MK-467 (90 μg kg-1 then 90 μg kg-1 hour-1 and 180 μg kg-1 then 180 μg kg-1 hour-1); loading doses were administered over 10 minutes. MAC was redetermined in duplicate starting 30 minutes after the start of drug administration at each dose. End-tidal sevoflurane concentrations were corrected for calibration and adjusted to sea level. A repeated-measures analysis was performed and comparisons between doses were conducted using Tukey's method. Statistical significance was considered at p<0.05.ResultsSevoflurane MAC decreased significantly from 1.86±0.3% to 1.04±0.1% and 0.57±0.1% with incremental doses of dexmedetomidine. Sevoflurane MAC significantly increased with high dose MK-467, from 1.93±0.3% to 2.29±0.5%.Conclusions And Clinical RelevanceDexmedetomidine caused a dose-dependent decrease in sevoflurane MAC, whereas MK-467 caused an increase in MAC at the higher infusion dose. Further studies evaluating the combined effects of dexmedetomidine and MK-467 on MAC and cardiovascular function may elucidate potential benefits of the addition of a peripheral α2-adrenergic antagonist to inhalation anesthesia in dogs.Copyright © 2017 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Ltd. All rights reserved.

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