Oxygen consumption--a comparison between calculation by Fick's principle and measurement by indirect calorimetry.

Oxygen consumption values calculated by Fick's principle (cVO2) were compared to simultaneously obtained values measured by indirect calorimetry (mVO2) in two groups of patients; post-coronary artery bypass graft (post-CABG) and septic shock. In both groups of patients, oxygen consumption values derived using indirect calorimetry were higher than that from Fick's principle. Whilst the bias obtained between the two methods of measurement were of acceptable amount clinically, the limits of agreement were wide: -57 to 51 ml.min-1.m-2 in the post-CABG group and -101 to 67 ml.min-1.m-2 in the group of septic patients; indicating that significant differences exist between paired individual values such that cVO2 and mVO2 were not interchangeable in this study.