The non-invasive determination of cardiac output in children: a three-breath technique.

In this study, the cardiac output of 11 children (5 days to 18 yr of age) was measured following cardiopulmonary bypass. Standard dye dilution cardiac outputs and an indirect Fick-CO2 technique were simultaneously determined. A rebreathing maneuver is described to estimate the oxygenated mixed venous PCO2 (PvCO2). This estimate of PvCO2 was combined with the end tidal PCO2 and CO2 production to give a non-invasive Fick estimate of the cardiac output. Non-invasive cardiac outputs correlated well with those measured by dye-dilution (r2 = 0.94) over a range of cardiac outputs from 490-7280 ml/min. All non-invasive determinations were within 15% of the line of identity, and within 22% of averaged replicate dye-dilution values. Our results agree with previous comparisons of indirect Fick-CO2 methods with invasive determinations of cardiac output. These data suggest that the indirect Fick-CO2 technique offers a rapid, non-invasive alternative to invasive monitoring of cardiac output.