Effects of a constant rate infusion of medetomidine–propofol on isoflurane minimum alveolar concentrations in horses

The aim of this investigation was to determine the isoflurane-sparing effect and impact on arterial blood pressure and anaesthetic recovery of a constant rate infusion of medetomidine–propofol in horses. In a prospective, crossover, randomised study, six healthy horses (mean ± SD age, 13.7 ± 7.7 years; weight, 433 ± 51 kg) were anaesthetised twice with isoflurane and were randomly assigned to receive one of two treatments on each occasion, at least 2 weeks apart. The first treatment was saline (CTL group) and the second a medetomidine–propofol infusion (MP group; 1.25 µg/kg/h medetomidine and 3 mg/kg/h propofol). The isoflurane minimum alveolar concentration (MAC) was determined and the reduction in anaesthetic requirements was calculated. Cardiopulmonary data were recorded at different intervals during the procedure and anaesthetic recovery was blindly assessed using three independent scales.The MAC in the MP group (0.43 ± 0.08%) was 65% lower than in the CTL group (1.23 ± 0.10%). The MP group had a higher mean arterial blood pressure and required less dobutamine than the CTL group. The recovery quality in both groups was considered fair or good and an improvement was observed using the Donaldson scale in the MP group. The administration of a medetomidine–propofol constant rate infusion reduced anaesthetic isoflurane requirements to a clinically significant extent and improved stability of arterial blood pressure together with a good quality recovery. This regime could be useful for providing balanced anaesthesia in horses.