Comparison between oxygen consumption calculated by Fick's principle using a continuous thermodilution technique and measured by indirect calorimetry.

We calculated oxygen consumption by the reverse Fick principle (cVO2) using cardiac output measured with a new technique of continuous thermal dilution and compared these values with measurements made at the same time using a gas exchange method (mVO2). We studied nine patients in a stable condition after cardiac surgery. In each patient six successive measurements of continuous cardiac output and mVO2 were made over 5 min at 10-min intervals. The mean difference between the estimates (mVO2-cVO2) was 15 ml min-1 m2 (95% confidence limits, -3 to 33 ml min-1 m2). The relative error of each method was 5% and 4% (continuous cardiac output and gas exchange methods, respectively). Calculation of VO2 using the new cardiac output technology had good repeatability compared with direct measurement, probably because of the high precision of measurement of cardiac output.