The ECOM® System uses three technologies (impedance, electrocardiography and arterial waveform analysis) to isolate and track beat-to-beat stroke volume. This combination approach avoids the shortcomings and vulnerabilities of individual techniques and provides back-up methodologies when individual approaches are compromised. The most critical facet is the ECOM® ET Tube that creates and monitors changes in impedance in an electrical field immediately adjacent to the ascending aorta. The ET Tube cuff electrodes are also the sources for R-Wave detection. By knowing when the ventricles are stimulated to eject blood (electrocardiography), and linking this information with the arterial blood waveform, the change in impedance of blood traversing the ascending aorta with each ventricular ejection is measured by the ECOM® System. The amount of blood pumped with each beat of the heart is stroke volume (SV). When SV is multiplied by heart rate, the result is cardiac output (CO). By inputting the patient's height and weight, a body surface area (BSA) value results, which when linked to the CO indexed values are also calculated and displayed as Cardiac Index (CI). Additionally, the arterial pressure data allow calculation of vascular resistance metrics. The waveform, primary derived values, and values derived by combining primary measures are displayed, monitored and trended on the Monitor.