Effect of body posture on cardiopulmonary function in horses during five hours of constant-dose halothane anesthesia.

This research investigates the impact of body positioning on the heart and lung function of horses under prolonged anesthesia with halothane. The study found that the position of the horse, lateral or dorsal recumbency, initially influences systemic arterial blood pressure and pulmonary artery pressure, but this difference disappears with time.

Composition of the Study

• The study involved seven healthy adult horses. Food was withheld from these horses prior to the study.
• These horses were anesthetized with a constant dose of 1.06% alveolar halothane for a duration of five hours.
• To notice the impact of body posture, comparisons were made between two different postures. In one instance, horses were placed on their sides (lateral recumbency – LR) and on another occasion they were on their backs (dorsal recumbency – DR).

Observations and Results

• The results confirmed previously reported findings that in LR, over time, there were increases in systemic arterial blood pressure, cardiac output, stroke volume, and PCV (Packed Cell Volume – a measure of the concentration of red cells in the blood).
• When horses were positioned in DR, systemic arterial blood pressure was initially significantly higher, and pulmonary artery pressure was lower when compared to similar periods in LR posture.
• However, over time, the changes in circulation based on body posture became insignificant.
• The only measurable difference remaining between the two poses was a higher heart rate at the 5th hour in DR.

Implications on Ventilation Measures

• Except for the measures of arterial oxygen pressure (PaO2), there were no significant changes noticed in ventilation measures in either LR or DR over time.
• The PaO2 was found to be significantly higher when horses were in LR compared to DR. However, this average difference did not drastically change over the duration of the anesthesia in either posture.

Overall, the study provides valuable insights on how different body postures can influence cardiovascular and respiratory functions in horses under prolonged, constant-dose halothane anesthesia. It underscores the importance of considering these factors in veterinary anesthesia practices for better medical outcomes.