Ideal Measurement of Cardiac Output: Is Impedance Cardiography the Answer?

The ideal measurement of cardiac output (CO) would be a system that is ac curate, noninvasive, reproducible, continuous, and technician-free. Impedence cardiography (ICG) has the promise of meeting these criteria. The authors have developed a unique ICG system that analyzes the analog signals from an impe dence cardiograph by an original software program. This was compared against standard thermodilution (TD) measurement of CO (CO TD) in patients in the in tensive care and heart surgical units. Simultaneous measurements by COTD and by COICG were performed in 65 patients. A good correlation was noted between COTD and COICG over a range of 2.4 to 9.7 L/min (r = 0.73, p < 0.002). If patients with factors known to inter fere with ICG were excluded, an improved correlation was found (r = 0.89, p < .002). COICG followed a similar trend as COTD even in these excluded pa tients. The reproducibility of the COICG was good (coefficient of variation = 0.071). The COICG was found to be simple and automatic. The results show that it is reproducible and correlates well with COTD. It also has the added advantages of being continuous and noninvasive. Factors such as arrhythmias, severe COPD, and mitral regurgitation were found to interfere with the COICG values. Over all, the versatility of. COICG gives the promise of very good noninvasive monitoring in critical care units and preoperative evaluation in the outpatient setting.