Dexmedetomidine-Tiletamine-Zolazepam Followed by Inhalant Anesthesia in Spectacled Bears (Tremarctos ornatus)

Natache Arouca Garofalo, André Augusto Justo, Stephanie Cristine Miyamoto Araújo, Mayara Travalini de Lima, Carlos Roberto Teixeira, Francisco José Teixeira Neto


Background: The spectacled bear (Tremarctos ornatus) is the only bear species inhabiting South America and is classified as vulnerable according to the International Union for Conservation of Nature (IUCN) Red List. Among the few publications on the use of general anesthesia and advanced monitoring of ursids in veterinary hospital settings, little is described regarding chemical restraint, general anesthesia and monitoring of spectacled bears. This case series describes the use of a dexmedetomidine-tiletamine-zolazepam chemical restraint combination and its effects on cardiorespiratory variables and arterial blood gases observed in two spectacled bears submitted to isoflurane anesthesia for imaging and/or surgical procedures.

Cases: Two female, one adult and one senile, all-term captive spectacled bears were referred to the Veterinary Medical Teaching Hospital at the Universidade Estadual Paulista - Unesp, Botucatu campus, both with a presumable history of recent trauma. After immobilization with an intramuscular (IM) administration of tiletamine-zolazepam (3.8 - 4.3 mg/kg) and dexmedetomidine (6.4 - 7.6 µg/kg), anesthesia induction was achieved by means of intravenous (IV) propofol (1 - 2 mg/kg). The patients then underwent isoflurane inhalant anesthesia and were submitted to intermittent positive-pressure ventilation through the remainder of the procedures. Initial settings of inspiratory flow rate were adjusted to obtain Ppeak of 10 cmH2O and tidal volumes (Vt) of 10 mL/kg, as well as respiratory rates (ƒR)and inspiration-to-expiration (I:E) ratio of 10 breaths/min and 1:2, respectively, and were then adjusted throughout anesthesia to maintain normocapnia (end-tidal carbon dioxide concentrations between35 and 45 mmHg). One of the individuals was chemically restrained (6.4 mg/kg of tiletamine-zolazepam and 7.7 µg/kg of dexmedetomidine) on a second anesthetic event for imaging procedures. Arterial blood gas analysis were performed with the subjects breathing room air and oxygen-enriched air. Both animals exhibited severe hypoxemia (partial pressure of oxygen [PaO2] < 60 mmHg) while breathing room air (inspired oxygen fraction [FiO2] ≅ 0.21). An impaired blood oxygenation (PaO2/FiO2 < 400) was still observed despite mechanical ventilation and the provision of 1.0 FiO2. Alveolar recruitment maneuvers (3 sequential mechanical sights with peak airway pressure at 20 - 30 cmH2O during 15 - 30 s each) were then performed, which resulted in improved PaO2/FiO2 ratios. All other blood gas, electrolytes and acid-base variables did not appear to be importantly altered by chemical restraint and general anesthesia.

Discussion: Dexmedetomidine-tiletamine-zolazepam resulted in reliable chemical restraints and is a feasible option for immobilizing spectacled bears, though severe hypoxemia may proceed. Hypoxemia is the most commonly described complication in bear anesthesia, and was also evidenced in the current report. However, low PaO2/FiO2 ratios tend to be accompanied by hypercapnia and therefore counteracted by oxygen supplementation in bears, which was not observed in the present report. In fact, blood oxygenation only reached regular values after alveolar recruitment maneuvers, which is compatible to an atelectasis-related hypoxemia. Therefore, either inhalant anesthesia or field chemical restraint should be accompanied by advanced monitoring (cardiorespiratory variables and blood gas analysis) in until further studies address the management of hypoxemia in spectacled bear. since Advanced monitoring was of major importance for a safe outcome and an uneventful recovery in this species.

Keywords: balanced anesthesia, dexmedetomidine, general anesthesia, spectacled bear, Tremarctos ornatus, wildlife.

Full Text:



Bouts T., Taylor P., Berry K., Routh A. & Gasthuys F. 2011. Evaluation of medetomidine-ketamine and dexmedetomidine-ketamine in Chinese water deer (Hydropotes inermis). Veterinary Anaesthesia and Analgesia. 38(2): 106-102.

Cattet M.R.L., Caulkett N.A. & Lunn N.J. 2003. Anesthesia of polar bears using xylazine-zolazepam-tiletamine or zolazepam-tiletamine. Journal of Wildlife Diseases. 39(3): 655-664.

Cattet M.R.L., Caulkett N. & Stenhouse G.B. 2003. Anesthesia of grizzly bears using xylazine-zolazepam-tiletamine or zolazepam-tiletamine. Ursus. 14(1): 88-93.

Caulkett N. & Cattet M.R.L. 1997. Physiological effects of medetomidine-zolazepam-tiletamine immobilization in black bears (Ursus americanus). Journal of Wildlife Diseases. 33(3): 618-622.

Caulkett N. & Cattet M.R.L. 2002. Anesthesia of Bears. In: Heard D. (Ed). Zoological Restraint and Anesthesia. Ithaca: International Veterinary Information Service, 6p.

Caulkett N. & Fahlman A. 2014. Ursids (Bears). In: West G., Heard D. & Caulkett N. (Eds). Zoo Animal and Wildlife Immobilization and Anesthesia. 2nd edn. Hoboken: John Wiley & Sons, pp.599-606.

Coltrane J.A., Farley S., Saalfeld D., Battle D., Carnahan T. & Teisberg J. 2015. Evaluation of Dexmedetomidine, Tiletamine, and Zolazepam for the Immobilization of Black Bears. Wildlife Society Bulletin. 39(2): 378-382.

D’Ovidio D., Noviello E. & Adami C. 2016. Nerve stimulator-guided sciatic-femoral nerve block in raptors undergoing surgical treatment of pododermatitis. Veterinary Anaesthesia and Analgesia. 42(4): 449-453.

Echeverry D.F., Laredo F.G., Gil F., Belda E., Soler M. & Agut A. 2012. Ultrasound-guided ‘two-in-one’ femoral and obturator nerve block in the dog: an anatomical study. Veterinary Anaesthesia and Analgesia. 39(6): 611-617.

Esteruelas N.F., Cattet M., Zedrosser A., Stenhouse G.B., Küker S., Evans A.L. & Arnemo J.M. 2017. Double-Blinded, Randomized Comparison of Medetomidine-Tiletamine-Zolazepam and Dexmedetomidine-Tiletamine-Zolazepam Anesthesia in Free-Ranging Brown Bears (Ursus arctos). Plos One. 12(1): 1-23.

Fahlman A., Arnemo J.M., Pringle J. & Nyman G. 2014. Oxygen supplementation in anesthetized brown bears (Ursus arctos) - How low can you go? Journal of Wildlife Diseases. 50(3): 574-581.

Fahlman A., Arnemo J.M., Swenson J.E., Pringle J., Brunberg S. & Nyman G. 2011. Physiologic evaluation of capture and anesthesia with medetomidine-zolazepam-tiletamine in brown bears (Ursus arctos). Journal of Zoo and Wildlife Medicine. 42(1): 1-11.

Fahlman A., Pringle J., Arnemo J.M., Swenson J.E., Brunberg S. & Nyman G. 2010. Treatment of hypoxemia during anesthesia of brown bears (Ursus arctos). Journal of Zoo and Wildlife Medicine. 41(1): 161-164.

Garofalo N.A., Teixeira Neto F.J., Alvaides R.K., Oliveira F.A., Pignaton W. & Pinheiro R.T. 2012. Agreement between direct, oscillometric and Doppler ultrasound blood pressures using three different cuff positions in anesthetized dogs. Veterinary Anaesthesia and Analgesia. 39(4): 324-334.

Jeong D., Yang J., Seok S., Song D. & Yeon S. 2016. Cardiorespiratory effects of isoflurane in Asiatic black bears (Ursus thibetanus) anesthetized with intramuscular medetomidine and zolazepam/tiletamine. The Journal of Veterinary Medical Science. 79(1): 153-159.

Kuusela E., Raekallio M., Anttila M., Falck I., Mölsäs S. & Vainio O. 2000. Clinical effects and pharmacokinetics of medetomidine and its enantiomers in dogs. Journal of Veterinary Pharmacology and Therapeutics. 23(1): 15-20.

Lemke K.A. 2004. Perioperative use of selective alpha-2 agonists and antagonists in small animals. The Canadian Veterinary Journal. 45(6): 475-480.

Lopes P.C.F., Nunes N., Sousa M.G., Nishimori C.T., Carareto R., Santos P.S.P & Camacho A.A. 2013. The effects of different inspired oxygen fractions on gas exchange and Tei-index of myocardial performance in propofol-anesthetized dogs. Veterinary Anaesthesia and Analgesia. 40(6): 573-583.

Marntell S., Nyman G. & Hedenstierna G. 2005. High inspired oxygen concentrations increase intrapulmonary shunt in anaesthetized horses. Veterinary Anaesthesia and Analgesia. 32(6): 338-347.

McEntire M.S., Hope K.L., Hayek L.C. & Siegal-Willott J.L. 2020. Review of anesthetic protocols in Andean bears (Tremarctos ornatus), sloth bears (Melursus ursinus), and giant pandas (Ailuropoda melanoleuca) at the Smithsonian Institution’s National Zoological Park, 1995-2016. Journal of Zoo and Wildlife Medicine. 51(1): 67-79.

Moens Y. 2013. Mechanical Ventilation and Respiratory Mechanics During Equine Anesthesia. Veterinary Clinics of North America: Equine Practice. 29(1): 51-67.

Onuma M. 2003. Immobilization of sun bears (Helarctos malayanus) with medetomidine-zolezepam-tiletamine. Journal of Zoo and Wildlife Medicine. 34(2): 202-205.

Portela D.A., Verdier N. & Otero P.E. 2018. Regional anesthetic techniques for the pelvic limb and abdominal wall in small animals: A review of the literature and technique description. The Veterinary Journal. 238: 27-40.

Romagnoli N., Pagnanelli G., Lambertini C., Drayton E., Buonacucina A. & Peli A. 2018. Cardiorespiratory effets of medetomidine and dexmedetomidine combined with tiletamine-zolazepam for the immobilization of Asiatic black bears (Ursus thibetanus) under isoflurane general anesthesia. Plos One. 13(7): 1-9.

Teisberg J.E., Farley S.D., Nelson O.L., Hilderbrand G.V., Madel M.J., Owen P.A., Erlenbach J.A. & Robbins C.T. 2014. Immobilization of grizzly bears (Ursus arctos) with dexmedetomidine, tiletamine and zolazepam. Journal of Wildlife Diseases. 50(1): 74-83.

The IUCN Red List of Threatened Species. 2017. Tremarctos ornatus. Available at


Copyright (c) 2021 Natache Arouca Garofalo, André Augusto Justo, Stephanie Cristine Miyamoto Araújo, Mayara Travalini de Lima, Carlos Roberto Teixeira, Francisco José Teixeira Neto

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.