Cardiac output technologies with special reference to the horse.

This research evaluates the different methods of measuring cardiac output in horses under various conditions and establishes lithium dilution as the most reliable technique for clinical use.

Understanding the Research

Cardiac output, which refers to the amount of blood the heart pumps through the circulatory system in a minute, is a critical factor in understanding the health and performance of horses during critical illness, anesthetic procedures, cardiovascular disease, or physical exercise. The ideal method of measuring this output should be accurate, easy to use, and minimally invasive for the horse.

Different Methods of Measuring Cardiac Output

This study unpacks the effectiveness and limitations of various procedures to measure cardiac output. This includes:

• The Fick Method: Despite historical usage for over a hundred years, this procedure was deemed too technically demanding for widespread clinical use. The Fick method measures cardiac output using the difference in oxygen content, between arterial and mixed venous blood along with the total volume of oxygen uptake by the lungs.
• Indicator Dilution Techniques: These techniques, which involve tracking the dilution of an ‘indicator’ substance in the bloodstream, were also evaluated. The study addressed three different indicators used – indocyanine green, thermodilution (cold), and lithium. Out of these, indocyanine green technique was found too complicated for regular use. Thermodilution procedure, despite being widely used in the past, was observed as risky since it requires direct catheterization into the heart’s right side. On the other hand, the lithium dilution method, which requires catheterization of a peripheral artery and a jugular vein, was validated as safe in both adult horses and neonatal foals.
• Doppler Echocardiography: This non-invasive ultrasound-based technique was noted as highly accurate. However, it also requires substantial technical expertise to operate correctly.
• Bioimpedance and Pulse Contour Analysis: While these two methods are newer, the research mentioned that they have not been validated in horses yet.

Conclusion

After detailed consideration of various methods, the study concludes that the lithium dilution method may be the best suited for clinical use when measuring cardiac output in horses. However, it does note that even this convenient and safe method needs further validation. The report calls for ongoing research and testing to find the most reliable, accessible, and minimally invasive procedures for measuring cardiac output in horses.