A Perspective on Non-invasive Continuous Cardiac Output in the Critically Ill

The thermodilution technique is the accepted clinical method of estimating cardiac output (CO), but it is discontinuous and requires the presence of a pulmonary artery catheter for as long as CO monitoring is needed. Continuous monitoring of CO allows for the detection of rapid effects on systemic flow and conductance that may otherwise remain unnoticed in a recording of arterial pressure or heart rate. We consider such information on the circulation beyond what is detected by arterial pressure, to be of relevance both in clinical medicine and in human cardiovascular research. Continuous information on systemic flow may be obtained from the arterial pressure wave. In this review, a perspective on non-invasive continuous CO is presented with a focus on the information about arterial flow that can be obtained from the non-invasive arterial pulse wave.