Cardiac output measurement by partial carbon dioxide rebreathing, 2-dimensional echocardiography, and lithium-dilution method in anesthetized neonatal foals.

This research aimed to evaluate the accuracy of two noninvasive methods to measure cardiac output in young, anesthetized horses by comparing them to the lithium-dilution method. Results show that one noninvasive method called volumetric echocardiography using the Bullet method can provide accurate and noninvasive estimations of cardiac output in this condition.

Methods Involved

• The research was carried out on ten neonatal foals, all of which were anesthetized.
• Cardiac output was manipulated by altering the depth of anesthesia and the infusion of dobutamine, a medication that enhances heart function.
• Different measurements of cardiac output were made concurrently using lithium dilution (the reference method), partial carbon dioxide rebreathing, transthoracic Doppler echocardiography, and volumetric echocardiography (which involved several formulas such as the cubic, Teichholz, Bullet, area-length, and single and biplane modified Simpson).

Results and Findings

• A total of thirty pairs of lithium-dilution/noninvasive cardiac output measurements were acquired from the ten foals.
• The relative bias of each method was determined as a percentage of the average cardiac output.
• The cardiac output measured through lithium dilution ranged from 3.09 to 11.1 L/min, resulting in cardiac indices between 79.0 and 209 mL/kg/min.
• The relative bias of the Doppler echocardiography method significantly increased while the relative bias of the partial carbon dioxide rebreathing method significantly decreased with increasing cardiac output.
• When considering methods not influenced by the level of cardiac output, the relative bias of the Bullet method was significantly lower than each of the other noninvasive methods evaluated.

Conclusions

• Volumetric echocardiography using the Bullet method has been found to provide an accurate and noninvasive estimate of cardiac output in anesthetized neonatal foals.
• Therefore, the use of this method merits further investigation in the monitoring of critically ill conscious foals.