Total intravenous anaesthesia in horses using medetomidine and propofol

Abstract

Objective: To examine the clinical suitability of medetomidine–propofol infusions for total intravenous anaesthesia in horses.
Animals: Fifty client-owned horses of mixed breed, age [mean ± SD (range)] 6.6 ± 4.4 (0.04–18) years, mass 478 ± 168.3 (80–700) kg presented for a range of operations requiring general anaesthesia.
Materials and methods: Pre-anaesthetic medication was intravenous (IV) medetomidine 7 μg kg−1. Anaesthesia was induced with IV ketamine (2 mg kg−1) and diazepam (0.02 mg kg−1). After endotracheal intubation, O2 was delivered (FiO2 > 0.85). Positive pressure ventilation was initiated if breath-holding in excess of 1 minute occurred. Anaesthesia was maintained with a constant rate medetomidine infusion (3.5 μg kg−1 hour−1) and propofol infused IV to effect (initial dose 0.1 mg kg−1 minute−1). Heart (HR) respiratory (fr) and propofol administration rates, and systemic arterial blood pressures were recorded at 5-minute intervals. Arterial blood gas (O2 and CO2) tensions and pH values were recorded every 15 minutes. Ten minutes after ending medetomidine–propofol infusion, medetomidine (2 μg kg−1; IV) was given. Cardiopulmonary data were analysed using descriptive statistical techniques.
Results: Thirty-three orthopaedic, seven integumentary and 10 elective abdominal operations were performed. Cardiopulmonary data, presented as range of mean individual (and absolute individual minimum and maximum values) were: HR: 28.0–39.2 (16–88) beats minute−1; mean arterial blood pressure: 74.0–132.5 (42–189) mmHg; PaO2: 22.1–42.9 (4.9–67.8) kPa; [166–322 (37–508) mmHg], PaCO2: 6.7–8.1 (4.2–11.8) kPa [50–61 (32–88) mmHg] and pH 7.35–7.39 (7.15–7.48). Positive pressure ventilation was required in 23 horses. In three horses, HR values below 20 beats minute−1 were treated with 20 μg kg−1 atropine (IV). Mean propofol infusion rates were 98–108 μg kg−1 minute−1. During anaesthesia, movement occurring in 14 horses was controlled with thiopental. Duration of anaesthesia was 111.6 ± 41.4 (46–225) minutes. Recovery in all horses was uneventful and completed within 42.2 ± 19.8 (12–98) minutes.
Conclusions and clinical relevance: Medetomidine–propofol infusion produces adequate conditions for a range of surgical procedures. Cardiovascular function was adequate, as no pressor agents were required. Positive pressure ventilation was required in 23 horses.