title: Cardiac output method comparison studies: the relation of the precision of agreement and the precision of method.
abstract: Cardiac output (CO) plays a crucial role in the hemodynamic management of critically ill patients treated in the intensive care unit and in surgical patients undergoing major surgery. In the field of cardiovascular dynamics, innovative techniques for CO determination are increasingly available. Therefore, the number of studies comparing these techniques with a reference, such as pulmonary artery thermodilution, is rapidly growing. There are mainly two outcomes of such method comparison studies: (1) the accuracy of agreement and (2) the precision of agreement. The precision of agreement depends on the precision of each method, i.e., the precision that the studied and the reference technique are able to achieve. We call this "precision of method". A decomposition of variance shows that method agreement does not only depend on the precision of method but also on another important source of variability, i.e., the method's general variability about the true values. Ignorance of that fact leads to falsified conclusions about the precision of method of the studied technique. In CO studies, serial measurements are frequently confused with repeated measurements. But as the actual CO of a subject changes from assessment to assessment, there is no real repetition of a measurement. This situation equals a scenario in which single measurements are given for multiple true values per subject. In such a case it is not possible to assess the precision of method.
authors.affiliation: Institute of Medical Statistics and Epidemiology, Klinikum rechts der Isar, Technische Universität München, Ismaninger Straße 22, 81675, Munich, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Hapfelmeier
authors.affiliation: Anaesthesia and Intensive Care, St George's Healthcare NHS Trust and St George's University of London, London, SW19 0QT, UK.|St George's Medical School, London, SW17 0QT, UK.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Cecconi
authors.affiliation: Department of Anesthesiology, Center of Anesthesiology and Intensive Care Medicine, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246, Hamburg, Germany. bernd.saugel@gmx.de.
authors.forename: Bernd
authors.initials: B
authors.lastname: Saugel
mesh_terms: D000465:Algorithms; D002302:Cardiac Output / Q000502:physiology*; D003627:Data Interpretation, Statistical; D006334:Heart Function Tests / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D054928:Validation Studies as Topic
keywords: Accuracy; Bland–Altman analysis; Cardiac output; Hemodynamic monitoring; Method comparison; Precision