Abstract
Objective To test if the addition of butorphanol by constant rate infusion (CRI) to medetomidine–isoflurane anaesthesia reduced isoflurane requirements, and influenced cardiopulmonary function and/or recovery characteristics.
Study design Prospective blinded randomised clinical trial.
Animals 61 horses undergoing elective surgery.
Methods Horses were sedated with intravenous (IV) medetomidine (7 μg kg−1); anaesthesia was induced with IV ketamine (2.2 mg kg−1) and diazepam (0.02 mg kg−1) and maintained with isoflurane and a CRI of medetomidine (3.5 μg kg−1 hour−1). Group MB (n = 31) received butorphanol CRI (25 μg kg−1 IV bolus then 25 μg kg−1 hour−1); Group M (n = 30) an equal volume of saline. Artificial ventilation maintained end-tidal CO2 in the normal range. Horses received lactated Ringer’s solution 5 mL kg−1 hour−1, dobutamine <1.25 μg kg−1 minute−1 and colloids if required. Inspired and exhaled gases, heart rate and mean arterial blood pressure (MAP) were monitored continuously; pH and arterial blood gases were measured every 30 minutes. Recovery was timed and scored. Data were analyzed using two way repeated measures anova, independent t-tests or Mann–Whitney Rank Sum test (p < 0.05).
Results There was no difference between groups with respect to anaesthesia duration, end-tidal isoflurane (MB: mean 1.06 ± SD 0.11, M: 1.05 ± 0.1%), MAP (MB: 88 ± 9, M: 87 ± 7 mmHg), heart rate (MB: 33 ± 6, M: 35 ± 8 beats minute−1), pH, PaO2 (MB: 19.2 ± 6.6, M: 18.2 ± 6.6 kPa) or PaCO2. Recovery times and quality did not differ between groups, but the time to extubation was significantly longer in group MB (26.9 ± 10.9 minutes) than in group M (20.4 ± 9.4 minutes).
Conclusion and clinical relevance Butorphanol CRI at the dose used does not decrease isoflurane requirements in horses anaesthetised with medetomidine–isoflurane and has no influence on cardiopulmonary function or recovery.
Bettschart-Wolfensberger, Regula