[Oxygen consumption by indirect calorimetry and Fick equation in swine: role of cardiac output].

Objectives: To compare O2 uptake values measured by indirect calorimetry (VO2R) with Fick-derived values (VO2Fick) over a wide range of VO2 in experimental conditions and to analyze the influence of cardiac output (QC) on the difference between VO2R and VO2Fick.
Study Design: Animal study.
Material: Nineteen 2.5-month-old, 29.2 +/- 2.8-kg, Large White pigs.
Methods: A step-by-step decrease in venous return was obtained either by haemorrhage or progressive inferior vena cava and portal veins clamping. Measurements, of 5 to 7 minutes duration included VO2R (Deltatrac), thermodilution QC and arterial and mixed venous blood O2-content. The VO2 values were compared using Bland and Altman's bias analysis. The relationship between QC values and relative error (ER = [VO2R - VO2Fick]/0.5x[VO2R + VO2Fick] was analyzed using a Spearman rank correlation coefficient.
Results: The VO2R and VO2Fick arithmetic mean ranged from 108 to 253 mL.min-1 in 130 measurements with broad limits of agreement between both methods. On average, VO2R values were higher than VO2Fick values by +15 +/- 25 mL.min-1. ER significantly decreased with QC (rs = 0.417; P = 0.0001).
Conclusion: VO2R values exceed VO2Fick values. This bias does not occur in the low QC range, presumably owing to artifactual over estimation of thermodilution QC.