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

Abstract

Objective To characterise a propofol-medetomidine-ketamine total intravenous anaesthetic protocol in impala (Aepyceros melampus). Study design Prospective clinical study. Animals Ten adult female impala, weighing 39 (±4) kg. Materials and methods Impala were immobilised with 2 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 min-1. Anaesthesia was maintained with a constant rate infusion of medetomidine and ketamine at 5 ?g kg-1 h-1 and 1 mg kg-1 h-1, respectively, and propofol to effect (initially 0.2 mg kg-1 min-1) for a period of 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 analysed intermittently. At 120 minutes maintenance the thiafentanil and medetomidine were antagonised using naltrexone (10:1 thiafentanil) and atipamezole (5:1 medetomidine), respectively, and recoveries scored. Results All impala were successfully immobilised, with a median (IQR) time to recumbency of 9.6 (7.2-14.4) minutes. The median (IQR) dose of propofol required for intubation was 2.7 (1.9-3.3) mg kg-1. The propofol-medetomidine-ketamine combination ensured recumbency for the 120 minute period. Propofol titration showed an erratic downward trend; a minimum infusion rate was not determined. Heart rate, respiratory rate and arterial blood pressure were well maintained. Arterial blood gas analysis indicated marked hypoxaemia, hypercapnia and acidosis. 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 9.4 (8.2-10.6) minutes. Conclusions and clinical relevance A propofol-medetomidine-ketamine combination can provide adequate anaesthesia for invasive procedures in impala for up to 120 minute duration. The propofol infusion should begin at 0.2 mg kg-1 min-1 and be titrated to clinical effect. Oxygen supplementation and airway protection with a cuffed endotracheal tube are essential.