Evaluation of a midazolam-ketamine-xylazine infusion for total intravenous anesthesia in horses.

The research evaluated the effectiveness of a combination of midazolam, ketamine, and xylazine for total intravenous anesthesia in horses, highlighting the potential benefits and limitations of such a technique.

Method

• In this research, six healthy Thoroughbred mares were assessed. The horses were first sedated with xylazine, which was administered intravenously at a dosage of 1.0 mg per kg of body weight.
• Anesthesia was then induced with midazolam (0.1 mg/kg), followed by ketamine (2.2 mg/kg), both given intravenously.
• The anesthesia was sustained by an intravenous infusion of the three drugs, with midazolam being administered at 0.002 mg/kg/minute, ketamine at 0.03 mg/kg/minute, and xylazine at 0.016 mg/kg/minute.
• During a 60-minute procedure involving surgical manipulation and injection of the palmar digital nerves, additional ketamine was provided if a horse displayed motor activity such as moving its head or limbs.
• Cardiopulmonary and arterial blood variables were measured before anesthesia, at different time points during the infusion (10, 20, 30, 45, and 60 minutes), and 10 minutes after the horses had regained their footing post-anesthesia.

Findings

• Anesthesia was effective for about 70 minutes post-induction. Four of the six horses needed supplemental ketamine during the procedures.
• All major cardiovascular variables, such as heart rate, respiratory rate, arterial blood pressures, and cardiac output remained steady and similar to pre-anesthesia levels throughout the IV anesthesia duration.
• However, the arterial partial pressure of oxygen and oxygen saturation of the arterial hemoglobin reduced significantly from pre-anesthesia levels throughout anesthesia, indicating decreased oxygen delivery between 10 and 30 minutes of infusion.
• The recovery period post-anesthesia was optimal: all horses regained their footing on their first attempt and recorded a median recovery score of 2, on a numeric scale where 1 indicated optimal recovery.

Conclusion

• The combination of midazolam, ketamine, and xylazine was effective in achieving total intravenous anesthesia in horses.
• However, the research suggests the need for further studies to explore different dosage levels of midazolam and ketamine, as well as the potential to substitute other α(2)-adrenoceptors for xylazine.