Do potent immobilising-opioids induce different physiological effects in impala and blesbok?

Potent opioids are known to cause negative alterations to the physiology of immobilised antelope. How these effects differ between species has not been studied. This study aimed to compare time to recumbence and effects of opioid-based immobilisation on the physiology of impala (Aepyceros melampus) and blesbok (Damaliscus pygargus phillipsi). Eight animals of each species were immobilised, with 0.09 mg/kg etorphine and 0.09 mg/kg thiafentanil respectively, in a randomised two-way cross-over study. Variables measured and analysed by means of a linear mixed model included time to recumbence, heart rate, respiratory rate, arterial blood pressure, blood gases, lactate and glucose. In blesbok, mean time to recumbence was not significantly different with either drug (2.5 minutes and 2.2 min, respectively), but in impala thiafentanil achieved a shorter time to recumbence (2.0 min) than etorphine (3.9 min). Mean heart rates of immobilised impala were within reported physiological limits, but lower in immobilised blesbok when both opioids were used (35 beats/min to 44 beats/min vs. 104 ± 1.4 beats/min resting heart rate). Impala developed severe respiratory compromise and hypoxaemia from both opioids (overall mean PaO2 values ranged from 38 mmHg to 59 mmHg over 30 min). In contrast, blesbok developed only moderate compromise. Therefore, significantly different species-specific physiological responses to potent opioid drugs exist in blesbok and impala. Given that these different responses are clinically relevant, extrapolation of immobilising drug effects from one species of African ungulate to another is not recommended.

Propofol-medetomidine-ketamine total intravenous anaesthesia in thiafentanil-medetomidine-immobilized impala (Aepyceros melampus).

OBJECTIVE: To characterize a propofol-medetomidine-ketamine total intravenous anaesthetic in impala (Aepyceros melampus). STUDY DESIGN: Prospective clinical study. ANIMALS: Ten adult female impala. MATERIALS AND METHODS: Impala were immobilized at 1253 m above sea level with 2.0 mg thiafentanil and 2.2 mg medetomidine via projectile darts. Propofol was given to effect (0.5 mg kg-1 boluses) to allow endotracheal intubation, following which oxygen was supplemented at 2 L minute-1. Anaesthesia was maintained with a constant-rate infusion of medetomidine and ketamine at 5 µg kg-1 hour-1 and 1.5 mg kg-1 hour-1, respectively, and propofol to effect (initially 0.2 mg kg-1 minute-1) for 120 minutes. The propofol infusion was titrated according to reaction to nociceptive stimuli every 15 minutes. Cardiopulmonary parameters were monitored continuously and arterial blood gas samples were analysed intermittently. After 120 minutes' maintenance, the thiafentanil and medetomidine were antagonized using naltrexone (10:1 thiafentanil) and atipamezole (5:1 medetomidine), respectively. RESULTS: All impala were successfully immobilized. The median dose [interquartile range (IQR)] of propofol required for intubation was 2.7 (1.9-3.3) mg kg-1. The propofol-medetomidine-ketamine combination abolished voluntary movement and ensured anaesthesia for the 120 minute period. Propofol titration showed a generally downward trend. Median (IQR) heart rate [57 (53-61) beats minute-1], respiratory rate [10 (9-12) breaths minute-1] and mean arterial blood pressure [101 (98-106) mmHg] were well maintained. Arterial blood gas analysis indicated hypoxaemia, hyper- capnia and acidaemia. Butorphanol (0.12 mg kg-1) was an essential rescue drug to counteract thiafentanil-induced respiratory depression. All impala regurgitated frequently during the maintenance period. Recovery was calm and rapid in all animals. Median (IQR) time to standing from antagonist administration was 4.4 (3.2-5.6) minutes. CONCLUSIONS AND CLINICAL RELEVANCE: A propofol-medetomidine-ketamine combination could provide adequate anaesthesia for invasive procedures in impala. The propofol infusion should begin at 0.2 mg kg-1 minute-1 and be titrated to clinical effect. Oxygen supplementation and airway protection with a cuffed endotracheal tube are essential.