[Comparison of cardiac output measured continuously by thermodilution and calculated according to Fick's principle]

Recently, a thermodilution technique for continuous measurement of cardiac output was introduced. The aim of this study was to evaluate the accuracy of continuous cardiac output measurement using the thermodilution technique (CCO) and to assess the correspondence between CCO and cardiac output obtained with the Fick's principle (Fick-CO). Nine patients were studied in the postoperative period after cardiac surgery. A new pulmonary artery catheter modified by attachment of a thermal filament (Intellicath, Model PA3-H-8Fr) was inserted and connected to a continuous cardiac output computer (Vigilance Monitor). Oxygen consumption was continuously measured using the gas exchange method (Deltatrac Metabolic Monitor). Fick-CO was calculated according to the Fick's principle. The study in each patient consisted of 6 serial determinations of both CCO and Fick-CO at 10 min intervals. For 54 pairs of measurements, the mean difference (Fick-CO-CCO) was 0,6 L.min-1. The limits of agreement were--0,6 to 1,8 L.min-1 respectively. The relative error was 6% for CCO and 10% for Fick-CO. It is concluded that CCO and Fick-CO cannot be considered as being interchangeable. However, the accuracy of CCO is acceptable. The technique does not require any user calibration and eliminates the need of bolus injections. Further studies are necessary to determine the benefits of this new technique in the various clinical situations.