Thermodilution estimation of cardiac output at high flows in anesthetized horses.

This study investigates the comparative accuracy of two techniques used for estimating cardiac output (the volume of blood pumped by the heart per minute) in anesthetized horses. The methods under comparison are thermodilution (measuring the dilution of a cold saline solution injected into the heart) and indocyanine green dye dilution. The study finds some differences in measurements, offering adjustments for more aligned results.

Methods and Techniques

• The horses involved in the study were anesthetized and their cardiac output was manipulated to produce different flow rates, specifically between 10 to 39 liters per minute.
• The cardiac output was estimated using two techniques for comparison. The first was the thermodilution technique where cold saline solution is used to cool the blood and the cardiac output is derived based on the time it takes for the blood temperature to return to baseline. The second technique involved using indocyanine green dye which is injected and diluted by the bloodstream, allowing for the estimation of cardiac output based on the concentration of dye detected at different points in time.
• The area of the dye dilution cardiac output curves was calculated by two different methods, the fore-‘n-aft (FA) triangle method and the logarithmic exponential extrapolation and summation method.

Results and Findings

• The FA estimations of the area under the curve were found to be higher than those obtained by logarithmic extrapolation. To harmonize results, a multiplicative adjustment of 0.837 was formulated.
• On average, the thermodilution estimates of cardiac output were greater than the adjusted FA determinations.
• To merge the results obtained from the two different measurement techniques, weighted linear regression was applied and a calibration adjustment was suggested: thermal dilution cardiac output divided by 1.048 equals indocyanine green dye dilution cardiac output.

Conclusion

• This study is a comprehensive comparison of the thermodilution estimation method and the indocyanine green dye dilution method for calculating cardiac output. It highlights the disparities between these two techniques and offers some adjustments to provide more comparable results. Such adjustments could lead to more accurate and consistent measurements in animal and potentially human healthcare.