Research Article: A Double-Blinded, Randomized Comparison of Medetomidine-Tiletamine-Zolazepam and Dexmedetomidine-Tiletamine-Zolazepam Anesthesia in Free-Ranging Brown Bears (Ursus Arctos)

Date Published: January 24, 2017

Publisher: Public Library of Science

Author(s): Núria Fandos Esteruelas, Marc Cattet, Andreas Zedrosser, Gordon B. Stenhouse, Susanne Küker, Alina L. Evans, Jon M. Arnemo, Francesco Staffieri.


We compared anesthetic features, blood parameters, and physiological responses to either medetomidine-tiletamine-zolazepam or dexmedetomidine-tiletamine-zolazepam using a double-blinded, randomized experimental design during 40 anesthetic events of free-ranging brown bears (Ursus arctos) either captured by helicopter in Sweden or by culvert trap in Canada. Induction was smooth and predictable with both anesthetic protocols. Induction time, the need for supplemental drugs to sustain anesthesia, and capture-related stress were analyzed using generalized linear models, but anesthetic protocol did not differentially affect these variables. Arterial blood gases and acid-base status, and physiological responses were examined using linear mixed models. We documented acidemia (pH of arterial blood < 7.35), hypoxemia (partial pressure of arterial oxygen < 80 mmHg), and hypercapnia (partial pressure of arterial carbon dioxide ≥ 45 mmHg) with both protocols. Arterial pH and oxygen partial pressure were similar between groups with the latter improving markedly after oxygen supplementation (p < 0.001). We documented dose-dependent effects of both anesthetic protocols on induction time and arterial oxygen partial pressure. The partial pressure of arterial carbon dioxide increased as respiratory rate increased with medetomidine-tiletamine-zolazepam, but not with dexmedetomidine-tiletamine-zolazepam, demonstrating a differential drug effect. Differences in heart rate, respiratory rate, and rectal temperature among bears could not be attributed to the anesthetic protocol. Heart rate increased with increasing rectal temperature (p < 0.001) and ordinal day of capture (p = 0.002). Respiratory rate was significantly higher in bears captured by helicopter in Sweden than in bears captured by culvert trap in Canada (p < 0.001). Rectal temperature significantly decreased over time (p ≤ 0.05). Overall, we did not find any benefit of using dexmedetomidine-tiletamine-zolazepam instead of medetomidine-tiletamine-zolazepam in the anesthesia of brown bears. Both drug combinations appeared to be safe and reliable for the anesthesia of free-ranging brown bears captured by helicopter or by culvert trap.

Partial Text

Capture, and anesthesia of wild mammals are required for conservation, research and management purposes [1–3]. The use of anesthetic drugs helps to reduce the stress and pain caused by capture and handling, while providing safety for capture personnel [4]. Brown bears (Ursus arctos) have been anesthetized for management and conservation throughout their global range using a variety of anesthetic agents. The most common protocols have combined a dissociative agent with a benzodiazepine or an alpha-2 adrenoceptor agonist [5, 6].

Both MTZ and DTZ proved to be safe and reliable drug combinations for anesthetizing free-ranging brown bears captured by helicopter and by culvert trap. However, we found no evidence to support use of DTZ as the better anesthetic combination. Both protocols produced a rapid onset of anesthesia, smooth induction, good analgesia and muscle relaxation, and smooth predictable recovery. Furthermore, the bears achieved an adequate plane of anesthesia for abdominal and subcutaneous surgeries, and muscle biopsies. We did not detect any bears’ reaction (i.e., increase in heart rate) to surgery.




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