Continuous Cardiac Output Monitoring: What Do Validation Studies Tell Us?

Several continuous cardiac output (CO) monitoring systems have been developed. None are ideal for use in anaesthesia or critical care. They all lack precision as shown by Bland–Altman studies. However, some provide reliable CO trending, which is useful for guiding fluid optimization protocols. The key issue is which systems are reliable, and this has not been helped by a lack of understanding of validation statistics in the literature. Recent studies suggest that none of the current intra-arterial pulse contour systems trend CO reliably. Stroke volume variability may provide a reliable alternative. Strangely, Nexfin finger plethysmography did reliably trend CO during routine surgery, but not during critical care. BioReactance also appears to trend CO acceptably, but its performance is affected by certain types of surgery that alter the pathways of electrical flux. Oesophageal Doppler is now well established for guiding goal-directed fluid regimens, and its trending of CO changes seems reliable.