Q What is noninvasive cardiac output monitoring and how does it work?

A Nancy M. Albert, RN, MSN, CCNS, CCRN, CNA replies:

There are many systems available (some in clinical trials) that have the capability of noninvasive monitoring of cardiac output. Some require arterial or central venous catheter connections to the monitoring device and are not truly noninvasive. One type of noninvasive system is called impedance cardiography (ICG) or thoracic electrical bioimpedance. This system works by injecting a constant, low-grade (1–4 mA) electrical current into the chest to sense change in thoracic electrical impedance that is associated with change in blood flow in the aorta during the cardiac cycle. During systole, a beat-to-beat voltage drop is associated with increased blood volume and flow in the aorta. The monitor assesses electrocardiogram and thoracic impedance changes to calculate stroke volume.1 Cardiac output is derived from the patient’s heart rate and stroke...

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