Comparison of a Guaifenesin, Ketamine, and Medetomidine Constant-Rate Infusion with Isoflurane Gas for Anesthesia Maintenance in American Black Bears (Ursus americanus)
American Association of Zoo Veterinarians Conference 2017
Kendra L. Bauer1, DVM; Jessica L. Siegal-Willott1, DVM, DACZM; Lee-Ann C. Hayek2, PhD; Nicole M. Luensman3, DVM, MS, CVMA, DACVAA; Tangara N. Cross1, CVT; Jaime L. Sajecki4, MS; David L. McRuer5, MSc, DVM, DACVPM
1Smithsonian Institution National Zoological Park, Smithsonian Conservation Biology Institute, Wildlife Health Sciences, Washington, D.C., USA; 2Mathematics and Statistics, the Smithsonian Institution, Washington, D.C., USA; 3Friendship Hospital for Animals, Washington, D.C., USA; 4Virginia Department of Game and Inland Fisheries, Henrico, VA, USA; 5Wildlife Center of Virginia, Waynesboro, VA, USA


Seven American black bears (Ursus americanus) were anesthetized in a crossover design with two different anesthetic maintenance protocols. The control protocol consisted of isoflurane gas started at 2%, and the experimental protocol consisted of a guaifenesin, medetomidine, ketamine (GMK) constant-rate infusion (CRI) started at a rate yielding 50 mg/kg/h guaifenesin, 0.01 mg/kg/h medetomidine, and 1 mg/kg/h ketamine. A consistent induction protocol of 2 mg/kg ketamine and 0.04 mg/kg medetomidine was used in both protocols. Induction and recovery times including times of first effect, recumbency, and hands on; length of maintenance protocol; time from reversals administered to head up, to standing on all four feet, to no ataxia, and to fully recovered were recorded and compared between protocols. Heart rate, respiratory rate, rectal temperature, blood pressure, end-tidal carbon dioxide, and hemoglobin oxygen saturation were recorded at 5-min intervals and compared between protocols. Venous blood gases taken at the beginning, end, and midway through the maintenance protocol were also collected and compared between protocols. All bears were mildly hypertensive with a mild respiratory acidosis. There were no statistically significant differences between the isoflurane and the GMK CRI maintenance protocols when comparing all other parameters measured, with the exception of extubation times and endpoint pCO2 measurements. There were no adverse events recorded with either protocol, and adequate depth of anesthesia was maintained. A GMK CRI provides a safe and more portable alternative to inhalant anesthetics for maintenance anesthesia in bears in captivity or in the field.


The authors thank Kendra Jacomo, Leigh-Ann Horne, Amy Kowalski, Helen Ingraham, and Dana Franzen for their participation and assistance during the study. The authors would also like to thank the generous donor that provided the funds for this research. All research was conducted under the Smithsonian National Zoological Park IACUC #16-11 and the Virginia Department of Game and Inland Fisheries Permit #056125.


Speaker Information
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Kendra L. Bauer, DVM
Smithsonian Institution National Zoological Park
Smithsonian Conservation Biology Institute
Wildlife Health Sciences
Washington D.C., USA

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