Induction of anesthesia and recovery in donkeys sedated with xylazine: a comparison of midazolam-alfaxalone and midazolam-ketamine

Objective To compare the induction and recovery characteristics and selected cardiopulmonary variables of midazolam-alfaxalone or midazolam- ketamine in donkeys sedated with xylazine. Study design Randomized, blinded, crossover experimental trial. Animals A group of seven adult male castrated donkeys weighing 164 +/- 14 kg. Methods Donkeys were randomly administered midazolam (0.05 mg kg(-1)) and alfaxalone (1 mg kg(-1)) or midazolam (0.05 mg kg(-1)) and ketamine (2.2 mg kg(-1)) intravenously following sedation with xylazine, with >= 7 days between treatments. Donkeys were not endotracheally intubated and breathed room air. Time to lateral recumbency, first movement, sternal recumbency and standing were recorded. Induction and recovery were assigned scores between 1 (very poor) and 5 (excellent). Heart rate (HR), respiratory rate (f(R)), invasive arterial blood pressures and arterial blood gases were measured before induction and every 5 minutes following induction until first movement. Results Time to lateral recumbency (mean +/- standard deviation) was shorter after alfaxalone (29 +/- 10 seconds) compared with ketamine (51 +/- 9 seconds; p = 0.01). Time to first movement was the same between treatments (27 versus 23 minutes). Time to standing was longer with alfaxalone (58 +/- 15 minutes) compared with ketamine (33 +/- 8 minutes; p = 0.01). Recovery score [median (range)] was of lower quality with alfaxalone [3 (2-5)] compared with ketamine [5 (3-5); p = 0.03]. There were no differences in HR, f(R) or arterial pressures between treatments. No clinically important differences in blood gases were identified between treatments. Five of seven donkeys administered alfaxalone became hypoxemic (PaO2 <60 mmHg; 8.0 kPa) and all donkeys administered ketamine became hypoxemic (p = 0.13). Conclusions and clinical relevance Both midazolam-alfaxalone and midazolam-ketamine produced acceptable anesthetic induction and recovery in donkeys after xylazine sedation. Hypoxemia occurred with both treatments.