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 mg 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, hypercapnia 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.