Comparison of noninvasive cardiac output measured by use of partial carbon dioxide rebreathing or the lithium dilution method in anesthetized foals.

The research compares two methods of measuring cardiac output (the amount of blood pumped by the heart per minute) in anesthetized foals: the partial CO2 rebreathing method (NICO) and the lithium dilution method (LiDCO). NICO is highlighted as a practical, noninvasive option for assessing cardiac output in neonatal foals with typical respiratory function.

Methodology

• The data used in this research was gathered from two other studies. These studies collectively assessed 18 newborn foals who weighed between 32 and 61 kg.
• The foals were anesthetized and instrumented to monitor direct blood pressure, heart rate, arterial blood gases, end-tidal levels of isoflurane and carbon dioxide, as well as cardiac output.
• Varying cardiac outputs were achieved by administering different medications (dobutamine, norepinephrine, vasopressin, phenylephrine, and isoflurane). This allowed for direct comparison between the LiDCO and NICO measurement methods.
• Measurements were taken two or three times, with a recovery period of 2 minutes between LiDCO measurements and 3 minutes between NICO measurements. A stable hemodynamic state had to be maintained for at least 10-15 minutes at each cardiac output level before measurements were taken.

Results

• In total, 217 comparisons were made between the two methods. The correlation was found to be quite good, at 0.77.
• On average, the LiDCO method gave measurements of 138 +/- 62 mL/kg/min while the NICO method gave measurements of 154 +/- 55 mL/kg/min.
• The mean difference (bias) between these two methods was -17.3 mL/kg/min with a precision (1.96 x SD) of 114 mL/kg/min. This shows that the NICO method generally gave slightly higher values.
• The mean of the differences of the two methods was 4.37 + (0.87 x NICO value).

Conclusion

• From the results obtained, it was concluded that the NICO method of measuring cardiac output is a viable, noninvasive technique to use with neonate foals that have normal respiratory function.
• This NICO method stood up well when compared to the more invasive LiDCO method.