COMPARISON OF INDIRECT CALORIMETRY AND THERMODILUTION CARDIAC-OUTPUT MEASUREMENT IN CHILDREN

We validated experimentally the ability of hood indirect calorimetry t o measure accurately (V) over dot O-2. For this purpose we compared ca rdiac output calculated from the Fick equation (Q) over dot = (V) over dot O-2/(Ca-O2 - C (V) over bar(O2)), in which (V) over dot O-2 was o btained by hood indirect calorimetry, to thermodilution cardiac output ((Q) over dot th) measured simultaneously during cardiac catheterizat ion in children (n = 16). Because FICO2 is a critical factor in hood i ndirect calorimetry calculations, we also assessed the consequence of taking into account measured FICO2 rather than using the usual standar d value of 0.0004. We found a good agreement between (Q) over dot and (Q) over dot th whether we used experimentally measured FICO2 in ambie nt air ((Q) over dot th = 0.89 (Q) over dot + 0.39, r = 0.941) or stan dard FICO2 (Q) over dot th = 0.84 (Q) over dot + 0.55, r = 0.930). How ever, (V) over dot CO2 and R computed from standard FICO2 differed sig nificantly (p < 0.001) from values derived from measured FICO2. This d emonstrates that indirect calorimetry allows reasonable estimates of ( Q) over dot, (V) over dot O-2, (V) over dot CO2, and R provided that t he actual values of FICO2 are used.