Physiological and behavioural effects of continuous remifentanil-xylazine administration in donkeys

Remifentanil and xylazine are used as continuous infusions to facilitate standing surgery in horses. Their use for this purpose has not been reported in donkeys.

To evaluate the behavioural, sedative, and cardiorespiratory effects of continuous intravenous infusion of remifentanil and xylazine in donkeys.

Non-blinded in vivo experiments.

Ten donkeys were sedated with an intravenous bolus of xylazine (0.8 mg/kg). After 3 min, continuous infusions of xylazine (0.65 mg/kg/h) and remifentanil (6 μg/kg/h) were administered for 60 min. Cardiorespiratory physiological parameters, rectal temperature, gastrointestinal motility, and sedation and ataxia scores were evaluated by a simple descriptive scale at M0 (baseline) and every 5 min, up to M60 (60 min), with scores 0-3. Head height concerning the ground was also evaluated. Dunnett and Friedman statistical tests (p < 0.05) were used.

Heart rate (p = 0.049) and respiratory rate (p = 0.001) decreased significantly at M10 and M5, respectively, compared to M0. There was a significant decrease in systolic (p = 0.04), mean (p = 0.02), and diastolic (p = 0.03) blood pressure at M15 compared to M0. The capillary refill time at M20 was statistically different (p = 0.001) from M0. The head height in relation to the ground reduced significantly from M5 (p = 0.001) to M60. Satisfactory sedation was obtained from M15 to M60. After stopping the infusion, all donkeys recovered successfully (7.1 ± 2.4 min). No adverse effects were observed during and after the infusion.

No painful stimulus or surgical procedure was performed.

Combining remifentanil and xylazine at the doses used caused adequate sedation and short recovery time. Remifentanil did not cause excitation in the donkeys. Future studies are necessary to test the protocol with painful stimuli.