Comparison of Fick and thermodilution cardiac output determinations in standing horses.

The research article is about comparing the efficiency of two techniques, Fick and thermodilution, used to measure cardiac output in horses. The study also investigates how these measurement methods perform under varied cardiac output conditions.

Study Objective and Methodology

The goal of the study was to evaluate and compare the effectiveness of two common methods for determining cardiac output in adult horses: the Fick method and thermodilution. The cardiac output is essentially the amount of blood the heart pumps out in a minute.

• The study involved six healthy, mature, resting horses. The average weight of the horses was approximately 517 kg.
• The researchers conducted the measurements in a calm setting where the horses were standing quietly.
• Through an advanced procedure, the horses had been equipped to enable the measurement of their cardiac output. Using Fick’s principle and the thermodilution techniques, the resting cardiac output was determined.

Adjustment of Cardiac Output Conditions

The cardiac output conditions were adjusted to see how the two measures perform in different scenarios.

• Initially, to increase the cardiac output, the researchers administered dobutamine infusion to the horses at a rate of 5 micrograms per kg of the horse’s weight per minute intravenously (IV).
• Then, to lower the cardiac output, the researchers administered a calming drug, xylazine, at a dosage of 0.5 mg/kg, also via IV.

Data Analysis and Conclusion

After collecting the data, the researchers compared the results from the Fick and thermodilution methods.

• The analysis was conducted using a statistical tool known as Bland-Altman analysis. This tool measures agreement (bias and precision) between two different ways of measuring the same thing.
• The mean difference (or bias) was found to be 1.88 L/min. The variability (or precision) between the two methods was found to be 24.17 L/min.
• To account for the size of the horses, the researchers normalized the cardiac output by calculating the cardiac index. In this case, the agreement between the two methods improved significantly with a resulting variability of 3.41 mL/kg/minute and a precision of 46.78 mL/kg/minute.
• The results suggest that these two methods, Fick’s principle and thermodilution, can provide valid and reasonably comparable measurements of cardiac output in horses. However, further research may be required to establish the most accurate method under varying conditions.