Cardiac Output Monitoring

OBJECTIVE: An increasing number of minimally or noninvasive devices are available to measure cardiac output in the critical care setting. This article reviews the underlying physical principles of these devices in addition to examining both animal and human comparative studies in an effort to allow clinicians to make informed decisions when selecting a device to measure cardiac output. DATA SOURCES: Peer-reviewed manuscripts indexed in PubMed. STUDY SELECTION: A systematic search of the PubMed database for articles describing the use of cardiac output monitors yielded 1,526 sources that were included in the analysis. DATA EXTRACTION: From all published cardiac output monitoring studies reviewed, the animal model, number of independent measurements, and correlation between techniques was extracted. DATA SYNTHESIS: Comparative studies in animals and humans between devices designed for measurement of cardiac output and experimental reference standards indicate thermodilution and Doppler-based techniques to have acceptable accuracy across a wide range of hemodynamic conditions, with bioimpedance techniques being less accurate. Thermodilution devices are marginally more accurate than Doppler-based devices but suffer from slower response time, increased invasiveness, and require stable core temperatures, good operator technique, and a competent tricuspid valve. Doppler-based techniques are less invasive and offer beat-to-beat measurements and excellent trending ability, but are dependent on accurate beam alignment and knowledge of aortic cross-sectional area. Studies of newer devices, such as pulse contour analysis, partial rebreathing, and pulse wave velocity, are far less in number and are primarily based on comparisons with thermodilution-based cardiac output measurements. Studies show widely ranging results. CONCLUSION: Thermodilution is relatively accurate for cardiac output measurements in both animals and humans when compared to experimental reference standards. Doppler-based techniques appear to have similar accuracy as thermodilution pulmonary artery catheters. Bioimpedance, pulse contour, partial rebreathing, and pulse wave velocity-based devices have not been studied as rigorously; however, the majority of studies included in this analysis point towards decreased accuracy.