Am. J. Respir. Crit. Care Med., Vol 155, No. 6, Jun 1997, 1930-1934.
Comparison of indirect calorimetry and thermodilution cardiac output measurement in children
A Capderou, D Douguet, J Losay and M Zelter
Hopital Marie-Lannelongue and Departement de Physiologie, Faculte deMedecine Pitie-Salpetriere, Paris, France.
We validated experimentally the ability of hood indirect calorimetry to
measure accurately VO2. For this purpose we compared cardiac output
calculated from the Fick equation Q = VO2/(Ca(O2) - CV(O2)), in which VO2
was obtained by hood indirect calorimetry, to thermodilution cardiac output
(Qth) measured simultaneously during cardiac catheterization in children (n
= 16). Because FI(CO2) is a critical factor in hood indirect calorimetry
calculations, we also assessed the consequence of taking into account
measured FI(CO2) rather than using the usual standard value of 0.0004. We
found a good agreement between Q and Qth whether we used experimentally
measured FI(CO2) in ambient air (Qth = 0.89 Q + 0.39, r = 0.941) or
standard FI(CO2) (Qth = 0.84 Q + 0.55, r = 0.930). However, VCO2 and R
computed from standard FI(CO2) differed significantly (p < 0.001) from
values derived from measured FI(CO2). This demonstrates that indirect
calorimetry allows reasonable estimates of Q, VO2, VCO2, and R provided
that the actual values of FI(CO2) are used.
