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Continuous cardiac output measurements do not agree with conventional bolus thermodilution cardiac output determination

[Les mesures continues du débit cardiaque ne concordent pas avec la détermination traditionnelle du débit cardiaque utilisant un bolus et la thermodilution]

Christian Zöllner, MD^*, Alwin E. Goetz, MD^*, Marion Weis, MD^*, Karl Mörstedt, MD^*, Bodo Pichler, MD^*, Peter Lamm, MD, Erich Kilger, MD^* and Mathias Haller, MD^*

^* From the Departments of Anesthesiology, and
Cardiac Surgery, Ludwig-Maximilians University of Munich, Munich, Germany.

Dr. Mathias Haller, Institut für Anaesthesiologie, Klinikum Grosshadern, Marchioninistrasse 15, 81377 München, Germany. Phone: +49-89-7095-2923; Fax: +49-89-7095-2822; E-mail: Mathias.Haller{at}bigfoot.de

Purpose: To evaluate the performance of two different continuous cardiac output monitoring systems based on the thermodilution principle in critically ill patients.

Methods: Nineteen cardiac surgical patients were randomly assigned to continuous cardiac output monitoring using one of the two systems under study (group I, IntelliCath^TM catheter, n=9; group II, Opti-Q^TM catheter, n=10). Each patient was studied over a period of three hours. Conventional bolus thermodilution cardiac output measurements were carried out every 15 min leading to 13 measurements in each patient. The continuous cardiac output values were compared with the bolus thermodilution measurements. Bias (mean difference between continuous and bolus thermodilution) and precision (SD of differences) were calculated as a measure of agreement between the respective continuous method and conventional bolus thermodilution.

Results: The range of measured cardiac outputs was 3.8–15.4 L•min^–1 (IntelliCath^TM) and 3.5–8.3 L•min^–1 (OptiQ^TM). Bias and precision was 0.06 ± 0.76 L•min^–1 (IntelliCath^TM) and -0.04 ± 0.74 L•min^–1 (OptiQ^TM), respectively. There was no difference in bias between the two systems (P=0.38). ± 2 SD of the differences (i.e., 95% of the differences) did not fall within the predetermined limits of agreement of ± 0.5 L•min^–1.

Conclusions: There was no difference between the two systems regarding the agreement with conventional bolus thermodilution as the standard. A discrepancy between bolus and continuous thermodilution cardiac output measurement techniques above the clinically acceptable limits suggest that they are not interchangeable.