Comparative Physiologic Effects During Carfentanil-Xylazine Anesthesia in North American Elk (Cervus elaphus) Supplemented with Nasopharyngeal Medical Air or Oxygen
This study compared specific cardiopulmonary effects and the overall quality of anesthesia during carfentanil-xylazine anesthesia in hypoxemic versus normoxemic elk.
Eight female habituated elk (Cervus elaphus) weighing 245±20 kg (mean ± SD) were studied with a randomized crossover design. Each elk was insufflated with oxygen (OXY) or medical air (AIR) through its nasopharynx at 10 L/min throughout anesthesia. Baseline data were collected before intramuscular (IM) injection of 10 µg/kg carfentanil (ZooPharm, Fort Collins, CO) and 0.2 mg/kg xylazine (Anased™, Vet-A-Mix, Shenandoah, IA). Arterial blood gases, direct arterial pressure, heart and respiratory rate, and somatic reflexes were assessed at three minute intervals for 30 minutes. Elk were reversed IM at 30 minutes with 1 mg/kg naltrexone (ZooPharm, Fort Collins, CO) and 2 mg/kg tolazoline (Lloyd Laboratories, Shenandoah, IA).
Induction and recovery times were analyzed with a paired t-test. Physiologic responses over time and between treatments were compared with one- and two-way ANOVA and a Bonferroni’s post hoc test. Incidence of rigidity and movement at different levels of PaO2 were compared with a chi-square test. Significance was set at p<0.05.
Induction and recovery times were significantly shorter in OXY, (208±39 sec) and (333±63) respectively, versus AIR, (306±84) and (532±201). Elk in OXY had significantly higher PaO2 and PaCO2, and significantly lower pH and heart rate compared to AIR. Maximum PaCO2 was 89±5 in OXY, and 64±4 mm Hg in AIR. Minimum PaO2 was 75±30 in OXY, and 28±6 mm Hg in AIR. There was a trend (p=0.08) towards decreased respiratory rate in OXY. Frequency of rigidity and movement increased at PaO2<70 mm Hg.
Animals nasally insufflated with air experienced slower inductions and recoveries, severe hypoxemia (PaO2<35 mm Hg), and increases in heart rate, muscle rigidity, and movement. The prolonged inductions and recoveries, as well as the physiologic features in AIR, are attributed to increased catecholamine release, decreased cerebral perfusion, and changes in blood-brain-barrier permeability in the face of severe hypoxemia.
Nasal insufflation of oxygen prevented hypoxemia and improved the quality of anesthesia but induced greater hypoventilation and respiratory acidosis. Oxygen supplementation in these elk offset complications related to hypoxemia but interfered with their hypoxic drive.
The authors thank Dr. Rob McCorkell for his invaluable assistance with the project. Major sources of funding for this project were provided by the Western College of Veterinary Medicine Research Fund, and the Saskatchewan Canada Agrifood Innovation Fund Specialized Livestock Research Trust.