Comparison of the effects of xylazine bolus versus medetomidine constant rate infusion on the stress response, urine production, and anesthetic recovery characteristics in horses anesthetized with isoflurane.

This research article investigates the comparative effects of two different anesthetics, xylazine and medetomidine, on horses. It concludes that the medetomidine has superior effects in terms of stress response, urine production and anesthetic recovery.

Study Design and Procedures

• This is a randomized crossover study performed on 10 healthy Standardbred horses.
• Each horse was premedicated with either xylazine or medetomidine through an intravenous line.
• The anesthesia was then induced using diazepam and ketamine and maintained with isoflurane for a period of 150 minutes.
• Two different methods were used for anesthesia management: one group received an end-tidal isoflurane concentration maintained at 1.7% and xylazine administered as a bolus at the end of anesthesia, while the other group received an end-tidal isoflurane concentration maintained at 1.4% and medetomidine infused throughout anesthesia.
• The horses’ serum cortisol and glucose concentrations were recorded before, during, and after the anesthesia, and the specific gravity and volume of their urine were measured during the anesthesia.
• The recovery from anesthesia was recorded by a digital video camera for later evaluation by two observers who were blinded to the anaesthetic treatments used.

Key Findings

• The research showed that, compared to the xylazine group, the medetomidine group had lower serum cortisol concentration and higher serum glucose level.
• The medetomidine group displayed longer sternal recumbency period, but no differences were observed between the two groups in terms of time to extubation, first movement or standing.
• The medetomidine group had significantly better mean attempt interval and visual analog recovery scores than the xylazine group.

Conclusion

• According to the results, medetomidine administered as a constant rate infusion proved to be more effective than xylazine in isoflurane-anesthetized horses. It provided a decreased stress response as indicated by lower serum cortisol levels, and showed superior anesthetic recovery characteristics.
• The use of medetomidine also resulted in increased serum glucose levels, though the implications of this need further study.