Errors in calculating cardiac output due to administration of perfluorochemicals.

Intravenous administration of perfluorochemicals (PFC) will alter the density (rho)B, the gravimetric specific heat (c)B, and the volumetric specific heat (rho c)B of blood. Changes in hematocrit also influence (rho c)B. The calibration constant employed in the determination of cardiac output (CO) by thermal dilution depends inversely on (rho c)B. We estimate the effect of addition of PFC and changes in hematocrit on (rho c)B. Consider blood to be a mixture of red cells, emulsified PFC particles, and plasma. This leads to the equation: (rho c)cB = 0.96 - 0.11Hct - 0.48Fct. Here Hct and Fct are the fractional volume concentrations of red blood cells and PFC, and (rho c)cB is the calculated specific heat based on the actual composition of blood. CO can be corrected for changes in (rho c)B by the equation: (CO)c = [(rho c)sB/(rho c)cB](CO)o. Here (CO)o is the observed cardiac output, (rho c)sB is the standard specific heat of blood used in the calculation of (CO)o, and (CO)c is the corrected cardiac output. We have observed laboratory situations where the correction factors have been as high as 10%.