Assessment of a medetomidin/propofol intravenous anaesthesia (TIVA) for clinical anaesthesia in equidae

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This study investigated the clinical use of a medetomidine/propofol TIVA technique in horses. Twenty-seven equidae of mixed breed, age [mean ± SD (range)] 2.9 ± 2.74 (0.11–11) years, weight (n = 15) 237 ± 130.22 (64–470) kg were anaesthetized for the following procedures: intra-abdominal (3); castration (15); joint flush (4); screw removal (1); desmotomy (3) and dermatoma removal (1). Horses were sedated with 7 µg kg−1 medetomidine IV and 10 minutes later anaesthesia was induced with 2 mg kg−1 propofol IV. Incremental doses of medetomidine were given prior to induction if the horse lifted its head when approached. Following induction, trachea were intubated and oxygen administered at FIO2 > 90%. Anaesthesia was maintained with 3.5 µg kg−1 h−1 medetomidine IV and propofol infused to effect (initial dose 0.1 mg kg−1min−1) 1. Heart rate, respiratory rate, propofol dose and arterial blood pressure were recorded every five minutes and arterial blood gases every 15 minutes. Quality of sedation, anaesthetic induction and recovery were evaluated by the first author according to previously described scores ( Bettschart-Wolfensberger et al. 1998). Data were analysed in a preliminary manner by descriptive statistical methods. Twelve horses required additional medetomidine for adequate sedation prior to induction (2 µg kg, n = 11; 6 µg kg, n = 1). Induction to anaesthesia was variable; excellent in 3, good in 18, fair in 4 and poor (unsatisfactory) in 2 horses. In an additional horse, induction to anaesthesia was very poor and transfer from the induction area to theatre was not possible, due to limb movement, even after several IV doses of propofol (total dose 2 mg kg−1) and thiopentone (total dose 2.5 mg kg−1). The use of propofol as an induction agent was stopped after this incident. During anaesthesia, range of mean values (absolute range) were, for respiratory rate 4.8–12.4 (4–32) min−1, heart rate 36.3–46.8 (15–58) min−1, mean arterial blood pressure 95.6–111 (84–128) mm Hg, propofol infusion 0.063–0.18 mg kg−1min−1, PaO2 23.2–31.8 (11.7–59.7) kPa, PaCO2 6.1–7 (5.2–8.5) kPa. Anaesthetic quality was excellent and spontaneous movement occurred in six horses but was slow and easily controlled with increments of propofol. Anaesthetic duration was 57.9 ± 38.16 (15–175) minutes. Recovery was completed unaided within 24.3 ± 10.66 (10–44.8) minutes. It was uneventful in all horses. Medetomidine/propofol TIVA at the dose rates studied produced good quality anaesthesia with cardiopulmonary depression within ranges commonly recorded during inhalation anaesthesia in horses. However the quality of the anaesthetic induction was variable, and appeared inferior to that achieved with induction techniques which included ketamine.