Mixed venous oxygen tension as an estimate of cardiac output in anesthetized horses.

This research aimed to explore the connection between mixed venous oxygen tension and cardiac output in anesthetized horses. The study concluded that there is a significant and closely related correlation between the two.

Objective of the Study

The core purpose of this research was to understand the relationship between mixed venous oxygen tension (referred to as PVO2) and cardiac output in six anesthetized horses. The researchers also intended to assess how xylazine, dobutamine, and Escherichia coli endotoxin, all substances administered to the horses, impacted this relationship.

Methods Employed

• The horses in the study were exposed to 100% oxygen during the study.
• Various parameters such as cardiac output, O2 consumption, mean arterial pressure, heart rate, and arterial and venous blood gases were measured post administration of xylazine or dobutamine.
• The study was conducted in different animal positions: lateral, sternal, and dorsal recumbencies.
• About three hours into the procedure, Escherichia coli endotoxin was administered while the horses were in the dorsal position, after which all measurements were repeated.
• The researchers then performed a linear regression analysis to evaluate the relationships between cardiac index (CI) and these factors: PVO2, heart rate, mean arterial pressure, jugular PVO2, and the PVO2 of blood from a superficial limb vein.

Key Findings

• The correlation between mean arterial pressure and cardiac index was significant in horses in all positions and even after endotoxin administration.
• Heart rate and cardiac index were significantly correlated in horses in all positions, but not after the administration of endotoxins.
• There was no significant correlation found between the PVO2 of blood from the jugular vein and a superficial limb vein in horses in the sternal position.
• Similarly, the PVO2 of blood from a superficial limb vein in horses in a lateral position did not significantly correlate with cardiac index.
• However, there was a significant and tight correlation found between PVO2 and cardiac index in horses in all positions and post endotoxin administration.

Conclusion

Through this study, the researchers demonstrated a significant correlation between cardiac output and mixed venous oxygen tension in anesthetized horses, in different positions, and even after administration of an endotoxin. The findings are particularly useful for estimating cardiac output in horses under similar conditions.