Effects of three immobilizing drug combinations on ventilation, gas exchange and metabolism in free-living African lions (Panthera leo)

Free-living lions (12 per group) were immobilized with tiletamine-zolazepam-medetomidine (TZM), ketamine-medetomidine (KM), or ketamine-butorphanol-medetomidine (KBM). During immobilization, respiratory, blood gas and acid-base variables were monitored for 30 minutes. Respiratory rates were within expected ranges and remained constant throughout the immobilizations. Ventilation increased in lions over the immobilization period from 27.2 ± 9.5 to 35.1 ± 25.4 L/min (TZM), 26.1 ± 14.3 to 28.4 ± 18.4 L/min (KM) and 23.2 ± 10.8 to 26.7 ± 14.2 L/min (KBM). Tidal volume increased over the immobilization period from 1800 ± 710 to 2380 ± 1930 mL/breath (TZM), 1580 ± 470 to 1640 ± 500 mL/breath (KM) and 1600 ± 730 to 1820 ± 880 mL/breath (KBM). Carbon dioxide production was initially lower in KBM (0.4 ± 0.2 L/min) than in TZM (0.5 ± 0.2 L/min) lions but increased over time in all groups. Oxygen consumption was 0.6 ± 0.2 L/min (TZM), 0.5 ± 0.2 L/min (KM) and 0.5 ± 0.2 L/min (KBM) and remained constant throughout the immobilization period. Initially the partial pressure of arterial oxygen was lower in KBM (74.0 ± 7.8 mmHg) than in TZM (78.5 ± 4.7 mmHg) lions, but increased to within expected range in all groups over time. The partial pressure of arterial carbon dioxide was higher throughout the immobilizations in KBM (34.5 ± 4.2 mmHg) than in TZM (32.6 ± 2.2 mmHg) and KM (32.6 ± 3.8 mmHg) lions. Alveolar-arterial gradients were initially elevated, but decreased over time for all groups, although in KM lions it remained elevated (26.9 ± 10.4 mmHg) above the expected normal. Overall, all three drug combinations caused minor respiratory and metabolic side-effects in the immobilized lions. However, initially hypoxaemia occurred as the drug combinations, and possibly the stress induced by the immobilization procedure, hinder alveoli oxygen gas exchange.