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

Overview

• This study investigated the effects of continuous intravenous infusion of remifentanil and xylazine on sedation, behaviour, and cardiorespiratory function in donkeys.
• The goal was to assess if this drug combination could be safely used for sedation during standing surgery in donkeys, similar to its use in horses.

Background

• Remifentanil is a short-acting opioid, often used for analgesia and sedation.
• Xylazine is an alpha-2 adrenergic agonist commonly used as a sedative and muscle relaxant in veterinary medicine.
• In horses, these drugs are infused continuously to maintain sedation during standing surgical procedures, avoiding general anesthesia risks.
• The effects of this combination in donkeys were not previously studied, despite physiological differences between species that can alter drug response.

Study Objective

• To evaluate how continuous remifentanil-xylazine infusion affects behavioural sedation, cardiorespiratory parameters, and physiological indicators in donkeys over 60 minutes.
• It focused on safety, sedation quality, and recovery time without involving any painful procedures or surgery.

Methods

• Subjects: 10 donkeys received an initial intravenous bolus of xylazine (0.8 mg/kg) to induce sedation.
• After 3 minutes, continuous infusions started: xylazine at 0.65 mg/kg/hour and remifentanil at 6 μg/kg/hour, maintained for 60 minutes.
• Physiological parameters monitored: heart rate, respiratory rate, blood pressure (systolic, mean, diastolic), capillary refill time, rectal temperature, and gastrointestinal motility.
• Behavioural assessments: sedation level, ataxia (loss of coordination), and head height relative to the ground, scored via a simple 0-3 scale every 5 minutes.
• Statistical tests (Dunnett and Friedman) identified significant changes compared to baseline (time zero, M0) with p < 0.05 considered significant.

Results

• Cardiorespiratory Effects:
• Heart rate significantly decreased by 10 minutes after infusion start (p=0.049).
• Respiratory rate dropped significantly by 5 minutes (p=0.001).
• Blood pressure (systolic, mean, diastolic) lowered significantly by 15 minutes (all p ≤ 0.04), suggesting a depressant effect on cardiovascular function.
• Capillary refill time was prolonged at 20 minutes, indicating altered peripheral perfusion (p=0.001).
• Behavioural and Sedation Observations:
• Head height decreased significantly from 5 minutes onward, reflecting postural relaxation/sedation (p=0.001).
• Satisfactory sedation scores were noted consistently from 15 minutes until the end of infusion (60 minutes).
• Ataxia was monitored but was not indicated as problematic in the abstract.
• Recovery:
• After stopping the drug infusion, donkeys recovered full function quickly, with a mean recovery time of approximately 7 minutes.
• No adverse effects or excitation (restlessness or agitation often caused by opioids) were observed during or post-infusion.

Conclusions

• The remifentanil-xylazine protocol at the studied doses produced effective sedation without adverse behavioural or cardiovascular effects in donkeys.
• Remifentanil did not cause excitation, a common opioid side effect, suggesting it may be well tolerated in this species.
• The combination allowed for a rapid and smooth recovery, important for clinical application.
• The study did not involve painful stimuli or surgery, so the efficacy of this sedation/analgesia protocol under such conditions remains untested.
• Future research is needed to evaluate these drugs during actual surgical procedures or painful interventions to confirm analgesic adequacy and safety.

Significance

• This research provides foundational data supporting remifentanil-xylazine continuous infusion as a viable sedation method in donkeys.
• It helps fill a species-specific knowledge gap since donkeys can differ significantly from horses in drug response.
• Clinicians may consider this protocol for standing sedation in veterinary procedures after further validation under surgical conditions.