Cardiac Output by Thermodilution and Arterial Pulse Contour Techniques

Abstract

A reliable method of cardiac output monitoring is particularly desirable in patients in the intensive care unit (ICU) and in patients undergoing cardiac, thoracic, or vascular interventions. As the patient’s hemodynamic status may change rapidly, continuous monitoring of cardiac output will provide information allowing rapid adjustment of therapy. Over the years, there has been a continuing development of new methods and devices to measure cardiac output, but none of these methods has gained unrestricted acceptance. Only the conventional thermodilution method has been generally accepted and is currently the clinical standard to which all other methods are compared. However, this method can only provide mean cardiac output if three or more single estimates are averaged, because individual thermodilution estimates show substantial scatter [1–4]. Also, the ‘recent breakthrough’ [5–9] of the ‘old’ transpulmonary thermodilution [10–13], as an alternative to the pulmonary artery catheter (PAC), needs three measurements to be averaged to reach sufficient precision. Three measurements with this system consume approximately 3 minutes. Therefore, these two thermodilution methods lack the ability to monitor cardiac output continuously. There are eight desirable characteristics for cardiac output monitoring techniques [14]: accuracy, reproducibility or precision, fast response time, operator independency, ease of use, continuous use, cost effectiveness, and no increased mortality and morbidity. Unfortunately, a technique which combines these eight characteristics has not become available yet. Consequently, in clinical practice the cardiac output measurement technique used varies depending on the preference of the treating physician and the available equipment.