Hemodynamic and respiratory effects of xylazine-morphine sulfate in horses.

This research article evaluates the effects of two different combinations of the drugs xylazine and morphine sulfate, administered intravenously, on the heart and lung functions of horses. The results showed significant changes in cardiac function and blood pressure, however, arterial blood gas tensions remained stable. The horses given a larger dose of morphine sulfate seemed to exhibit stronger analgesic effects.

Research Methodology

• The research involved administering two different intravenous combinations of xylazine and morphine sulfate to horses. Xylazine was administered at a fixed dosage (0.66 mg/kg of body weight) in both scenarios. However, the dosage of morphine sulfate varied; experiment 1 used 0.12 mg/kg, and experiment 2 used 0.66 mg/kg.
• The researchers closely monitored the horses’ heart rate, cardiac output, respiratory rate, central venous pressure, arterial and pulmonary arterial blood pressures, and arterial blood gas tensions (PaCO2 and PaO2).
• Both objective (trained personnel) and semi-objective evaluations were undertaken to assess the analgesic effects on the horses.

Research Findings

• The first experiment saw notable decreases in heart rate, cardiac output, and respiratory rate, and an increase in central venous pressure. The arterial and pulmonary arterial blood pressures also increased, but these changes were only temporary. Importantly, arterial blood gas tensions (PaCO2 and PaO2) and pH remained constant throughout the experiment.
• In the second experiment, where a larger dose of morphine sulfate was used, the observed reactions were similar to those in the first experiment, with the exception of heart rate, which did not decrease significantly.
• During both experiments, the horses did not exhibit any violent reactions such as kicking or striking, indicating a calming effect from the drug combinations.
• Both the objective and semi-objective assessments suggested an improvement in analgesic effects in the second experiment when compared to the first, implying a positive correlation between the dosage of morphine sulfate and the analgesic effect.

Conclusion

• The researchers concluded that the intravenous administration of xylazine and morphine sulfate led to significant changes in the horses’ cardiopulmonary functions. Despite these changes, the arterial blood gas tensions stayed constant, even when larger morphine sulfate dosages were administered.
• Interestingly, the horses subjected to the experiment did not exhibit any aggressive behaviours, indicating a significant analgesic effect of the drug combinations. The study seems to suggest a positive correlation between the dosage of morphine sulfate and the level of analgesia.