Effect of dexmedetomidine and xylazine followed by MK-467 on gastrointestinal microperfusion in anaesthetized horses.

The study investigates the impact of MK-467 on horses in combination with isoflurane anaesthesia and either xylazine or dexmedetomidine. The results suggest MK-467 reduces arterial blood pressure and systemic vascular resistance but increases cardiac index and decreases gastrointestinal microperfusion, likely due to inadequate perfusion pressure.

Methodology and Approach

• The research conducted was a prospective, randomized experimental trial involving 15 warmblood horses.
• The horses were split into two groups to receive either dexmedetomidine or xylazine for premedication, and as a constant rate infusion during isoflurane anaesthesia.
• Various health parameters were measured during anaesthesia, including heart rate, mean arterial blood pressure (MAP), systemic vascular resistance index (SVRI), and cardiac index (CI). The authors also observed microperfusion in the colon, jejunum, and stomach using laser Doppler flowmetry.
• Following 2 hours of stabilization, the horses were administered MK-467, and the mentioned parameters were measured for an additional 90 minutes.

Findings

• No differences were noted in the baseline measurements between the two groups.
• Administration of MK-467 resulted in a significant decrease in MAP and SVRI in both groups, with the effects lasting longer in the dexmedetomidine group.
• Despite an increased CI in both groups, the study found a decrease in microperfusion in the colon, jejunum, and stomach.
• The results suggest that the vasoconstriction induced by alpha-2-agonist was reversed by the administered dose of MK-467, leading to hypotension and an increase in CI. However, the gastrointestinal microperfusion years decreased, probably due to insufficient perfusion pressure.

Conclusions and Further Research

• The study concludes that the MK-467 dosage used reversed alpha-2-agonist vasoconstriction, causing a rise in CI and hypotension.
• The resulting decrease in gastrointestinal microperfusion indicates that insufficient perfusion pressure may be a side effect of this treatment strategy.
• The research suggests the need to determine an infusion rate for MK-467, as well as the ideal ratio between agonist and antagonist.