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A clinical study on the effect in horses during medetomidine-isoflurane anaesthesia, of butorphanol constant rate infusion on isoflurane requirements, on cardiopulmonary function and on recovery characteristics
- Bettschart-Wolfensberger, Regula, Dicht, Sidonia, Vullo, Cecilia, Frotzler, Angela, Kuemmerle, Jan M., Ringer, Simone K.
- Veterinary anaesthesia and analgesia 2011 v.38 no.3 pp. 186-194
- anesthesia, blood gases, blood pH, blood pressure, butorphanol, clinical trials, colloids, diazepam, gases, heart rate, horses, isoflurane, ketamine, medetomidine, prospective studies, surgery
- 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.