Cardiac output monitoring: basic science and clinical application.

Derangements in the circulation are a common feature of sepsis, trauma, major surgery and other critical illnesses. Detailed evaluation of the circulation is therefore an essential aspect of the clinical management of such patients. The use of cardiac output monitoring technology is an increasingly important aspect of evaluating patients in the operating theatre, critical care unit and elsewhere. There are now a number of different technologies available for this purpose, which use a diverse range of physiological principles. A detailed understanding of the physiological principles applied by such technology is essential for safe and effective use in clinical practice. The aim of this article is to describe the physiological principles used to measure cardiac output and their application in various monitors in common clinical use.