OXYGEN SUPPLEMENTATION IN ANESTHETIZED BROWN BEARS (URSUS ARCTOS)—HOW LOW CAN YOU GO? A ˚ sa Fahlman, 1,5 Jon M. Arnemo, 2,3 John Pringle, 1 and Go ¨ rel Nyman 4 1 Department of Clinical Sciences, Faculty of Veterinary Medicine and Animal Science, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden 2 Department of Forestry and Wildlife Management, Faculty of Applied Ecology and Agricultural Sciences, Hedmark University College, Campus Evenstad, NO-2418 Elverum, Norway 3 Department of Wildlife, Fish, and Environmental Studies, Faculty of Forest Sciences, Swedish University of Agricultural Sciences, SE-901 83 Umea ˚ , Sweden 4 Department of Animal Environment and Health, Faculty of Veterinary Medicine and Animal Science, Swedish University of Agricultural Sciences, SE-532 23 Skara, Sweden 5 Corresponding author (email: asa_fahlman@hotmail.com) ABSTRACT: Hypoxemia is anticipated during wildlife anesthesia and thus should be prevented. We evaluated the efficacy of low flow rates of supplemental oxygen for improvement of arterial oxygenation in anesthetized brown bears (Ursus arctos). The study included 32 free-ranging brown bears (yearlings, subadults, and adults; body mass 12–250 kg) that were darted with medetomidine- zolazepam-tiletamine (MZT) from a helicopter in Sweden. During anesthesia, oxygen was administered intranasally from portable oxygen cylinders at different flow rates (0.5–3 L/min). Arterial blood samples were collected before (pre-O 2 ), during, and after oxygen therapy and immediately processed with a portable analyzer. Rectal temperature, respiratory rate, heart rate, and pulse oximetry-derived hemoglobin oxygen saturation were recorded. Intranasal oxygen supplementation at the evaluated flow rates significantly increased the partial pressure of arterial oxygen (PaO 2 ) from pre-O 2 values of 9.161.3 (6.3–10.9) kPa to 20.466.8 (11.1–38.7) kPa during oxygen therapy. When oxygen therapy was discontinued, the PaO 2 decreased to values not significantly different from the pre-O 2 values. In relation to the body mass of the bears, the following oxygen flow rates are recommended: 0.5 L/min to bears ,51 kg, 1 L/min to bears 51– 100 kg, 2 L/min to bears 101–200 kg, and 3 L/min to bears 201–250 kg. In conclusion, low flow rates of intranasal oxygen were sufficient to improve arterial oxygenation in brown bears anesthetized with MZT. Because hypoxemia quickly recurred when oxygen was discontinued, oxygen supplementation should be provided continuously throughout anesthesia. Key words: Anesthesia, brown bear, flow rate, hypoxemia, immobilization, oxygen therapy, wildlife. INTRODUCTION Impaired oxygenation during anesthesia can lead to morbidity and mortality during and after the anesthetic event. Most physiologic studies that include blood gas analysis demonstrate hypoxemia with the drugs and doses used for anesthesia in free-ranging and captive wild animals (Read 2003; Mich et al. 2008; Fahlman et al. 2012). Mild to marked hypoxemia has been documented in free-ranging and captive brown bears (Ursus arctos) anes- thetized with medetomidine-zolazepam- tiletamine (MZT; Fahlman et al. 2011). Hypoxemia is anticipated and thus should be prevented during wildlife anesthesia. Intranasal oxygen supplementation is a simple and efficient method to increase arterial oxygenation, as documented in some wildlife species (Cattet et al. 2003; Fahlman et al. 2010, 2012). In brown bears, the use of intranasal oxygen at flow rates as high as 6–10 L/min has been reported (Mortenson and Bechert 2001; Cattet et al. 2003). Lower flow rates (2–5 L/min) efficiently treated hypoxemic brown bears on the basis of arterial blood gas analysis (Fahlman et al. 2010), but optimal flow rates to maintain adequate arterial oxygen- ation have not been established. Oxygen sources used in the field include oxygen cylinders that store gaseous oxygen under high pressure and portable battery- driven oxygen concentrators that extract nitrogen from the air and produce oxygen on site (Fahlman et al. 2010, 2012). Small light-weight oxygen cylinders are easy to DOI: 10.7589/2013-06-148 Journal of Wildlife Diseases, 50(3), 2014, pp. 574–581 # Wildlife Disease Association 2014 574