600 AJVR • Vol 79 • No. 6 • June 2018 A mazon parrots and other parrot species frequently require general anesthesia to enable veterinarians to perform medical or surgical treatments. General an- esthesia of birds is most commonly accomplished with inhalation agents such as isoflurane and sevoflurane. Inhalation anesthetic agents have the advantage of al- lowing rapid changes in anesthetic depth, and recovery from anesthesia is generally rapid because inhalation anesthetics are eliminated via the respiratory system. However, inhalation anesthetic agents can induce car- diovascular and respiratory depression, which may be life-threatening, especially in compromised patients. 1 Balanced anesthesia techniques, which are achieved by combining inhalation anesthetics with Effects of three fentanyl plasma concentrations on the minimum alveolar concentration of isoflurane in Hispaniolan Amazon parrots (Amazona ventralis) Michelle G. Hawkins VMD Peter J. Pascoe BVSC Heather K. DiMaio Knych DVM, PhD Tracy L. Drazenovich DVM Philip H. Kass DVM, PhD David Sanchez-Migallon Guzman LV , MS Received March 4, 2017. Accepted September 11, 2017. From the Departments of Medicine and Epidemi- ology (Hawkins, Drazenovich, Sanchez-Migallon Guzman), Surgical and Radiological Sciences (Pascoe), and Population Health and Reproduction (Kass), and the K. L. Maddy Equine Analytical Chemistry Labora- tory, California Animal Health and Food Safety Labo- ratory (DiMaio Knych), School of Veterinary Medi- cine, University of California-Davis, Davis, CA 95616. Address correspondence to Dr. Hawkins (mghawkins@ ucdavis.edu). OBJECTIVE To determine effects of 3 plasma concentrations of fentanyl on the mini- mum alveolar concentration of isofurane (MAC iso ) and cardiovascular vari- ables in Hispaniolan Amazon parrots (Amazona ventralis). ANIMALS 6 adult parrots. PROCEDURES In phase 1, anesthesia was induced and maintained with isofurane; inter- mittent positive-pressure ventilation was provided. The MAC iso was de- termined for each bird by use of a bracketing method and supramaximal electrical stimulus. Fentanyl (20 μg/kg) was administered IV, and blood samples were collected over time to measure plasma fentanyl concentra- tions for pharmacokinetic calculations. In phase 2, pharmacokinetic values for individual birds were used for administration of fentanyl to achieve tar- get plasma concentrations of 8, 16, and 32 ng/mL. At each concentration, MAC iso and cardiovascular variables were determined. Data were analyzed with mixed-effects multilevel linear regression analysis. RESULTS Mean ± SD fentanyl plasma concentrations were 0 ng/mL, 5.01 ± 1.53 ng/ mL, 12.12 ± 3.58 ng/mL, and 24.93 ± 4.13 ng/mL, and MAC iso values were 2.09 ± 0.17%, 1.45 ± 0.32%, 1.34 ± 0.31%, and 0.95 ± 0.14% for fentanyl target concentrations of 0, 8, 16, and 32 ng/mL, respectively. Fentanyl sig- nifcantly decreased MAC iso in a dose-dependent manner. Heart rate and blood pressure signifcantly decreased at all fentanyl doses, compared with values for MAC iso at 0 ng of fentanyl/mL. CONCLUSIONS AND CLINICAL RELEVANCE Fentanyl signifcantly decreased the MAC iso in healthy Hispaniolan Amazon parrots, but this was accompanied by a depressive effect on heart rate and blood pressure that would need to be considered for application of this technique in clinical settings. (Am J Vet Res 2018;79:600–605) other drugs such as parenterally administered opi- oids, are commonly used in mammals to reduce car- diovascular depression by reducing the necessary concentrations of the inhalation anesthetics. 2 Fenta- nyl citrate, a synthetic injectable μ-opioid receptor agonist, has been used extensively in both human and veterinary medicine because of its rapid onset and short duration of action. 3 Studies in humans, 4 dogs, 5 rats, 6 and red-tailed hawks (Buteo jamaicensis) 7 have revealed that fentanyl significantly reduces the MAC iso , and greater hemodynamic stability is achieved when fentanyl is used as part of a bal- anced anesthetic technique, compared with results when an inhalation agent is used alone. However, responses differ among species. 2,4–7 A steep reduc- tion (63%) in MAC iso is evident in people when a fentanyl plasma concentration of 3 ng/mL is achieved, and increases in plasma concentrations up to 10 ng/mL only lead to a further reduction of ABREVIATIONS MAC Minimum alveolar concentration MAC iso Minimum alveolar concentration of isofurane PETCO 2 End-tidal partial pressure of carbon dioxide