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

Abstract

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.

Cardiorespiratory effects of medetomidine and dexmedetomidine combined with tiletamine-zolazepam for the immobilization of Asiatic black bears (Ursus thibetanus) under isoflurane general anesthesia

“…In the present study, the mean induction time in both groups was longer than that reported for other bear species [ 3 , 10 ]. In these previous reports, the anesthetized bears were free-ranging animals which were pursued with a helicopter.…”

“…No bears in this study vomited or showed sign of vomiting. The advantages of combining alpha-2 agonist with tiletamine and zolazepam are a smooth and rapid induction and a smaller induction dose as previously reported in several papers [ 6 , 9 , 10 ].…”

“…A limitation of our study is that a blood gas evaluation was not carried out to monitor the PaO 2 . In addition, hemoglobin oxygen saturation was measured only with a pulse oximeter which has been described to be an unreliable indicator of hypoxemia in bears [ 10 , 16 ]. Another important finding during the capture of free-ranging bears was the alteration in body temperature; hyperthermia or hypothermia have been reported especially during anesthesia with helicopter capture [ 3 , 9 , 10 , 15 ].…”

“…Medetomidine (M) is a highly selective alpha-2 agonist; it is a racemic mixture of two enantiomers: dexmedetomidine and levomedetomidine. The combination of medetomidine-tiletamine-zolazepam (MTZ) has been used in many species of bears [ 7 , 9 , 10 ], including the Asiatic black bear ( U . thibetanus ) [ 3 ].…”

“…In brown bears ( Ursus arctos ), the combination of dexmedetomidine-tiletamine-zolazepam (DTZ) induces less hypoventilation and no hypoxia as compared with MTZ [ 11 ]. However, Fandos Esteruelas and collegues [ 10 ] did not find any differences in respiratory function and partial pressure of oxygen (PaO 2 ) when MTZ and DTZ were compared in immobilizing brown bears ( Ursus arctos ).…”