Effects of inhalation anesthetic agents on response of horses to three hours of hypoxemia.

The study explores the impact of different types of inhalation anesthesia on the biological responses of horses to hypoxemia. The researchers concluded that Isoflurane resulted in less muscular injury in hypoxemic horses than Halothane, suggesting Isoflurane is a better choice for hypoxemic horses.

Research Aim and Methodology

• The goal of this research was to understand how different types of inhaled anesthetics—Halothane and Isoflurane—alter the response of horses to three hours of hypoxemia (a condition characterized by low levels of oxygen in the blood).
• The researchers employed a controlled crossover study design, involving five healthy adult horses. Each horse served as its own control, receiving both types of anesthesia in separate trials.
• Each horse was anesthetized two times, once with Halothane and once with Isoflurane, while positioned in the left lateral recumbency (lying on the left side).
• The horses’ vital parameters, such as oxygen and carbon dioxide levels in the blood (PaO2 and PaCO2), were maintained at certain values for three hours while measurements were taken at regular intervals.
• Blood samples were also collected for biochemical analysis before the procedure, immediately after the horses stood up, and 1, 2, 4, and 7 days post-anesthesia.

Research Findings

• The cardiac index (a measure of the heart’s performance) during the anesthesia was found to be higher when Isoflurane was used as compared to Halothane.
• Interestingly, the cardiac index remained constant during the 3-hour hypoxemia period in the case of Halothane; however, it decreased when Isoflurane was used. Generally, a drop in cardiac index is not desirable, but further observations suggest otherwise.
• Despite having marginal non-significant P-values, certain differences were noted in arterial oxygen content and oxygen delivery between the two anesthetic agents.
• It was observed that the activity of certain enzymes (aspartate transaminase and sorbitol dehydrogenase) were higher in horses treated with Halothane, an indication of liver injury, suggesting that Halothane might be associated with hepatic insult.
• Finally, the study hinted that Isoflurane anesthetized horses experienced less circulatory disruption and muscular damage during hypoxemia than Halothane-anesthetized horses.

Conclusion

• The researchers concluded that in the cases of hypoxemic horses, Isoflurane appears to be a more advisable inhalation anesthetic compared to Halothane.
• The study provides valuable insights for veterinary practice, offering recommendations for a suitable anesthetic in treating hypoxemic animals, especially horses.
• However, because of the study’s small sample size, the applications of the results to a broader population of horses may be limited, suggesting the need for further research with larger randomized trials.