Absolute determination of cardiac output in intra-aortic balloon pumped patients using the radial arterial pressure trace.

We describe a new method for the absolute determination of cardiac output in intra-aortic balloon pumped (IABP) patients. The method uses the known pumping volume of the IABP balloon and the radial arterial pressure trace, which is commonly used to monitor IABP patients, to determine the cardiac output. Two pressure excursions denoted by P1-P0 and P2-P0, characterizing IABP balloon deflation, and ventricular ejection, respectively, are extracted from the radial trace. The cardiac output (CO) is then determined by the simple relation: CO = (BV) x (P2-P0)/(P1-P0) x HR where HR is the heart rate, and the value for pumped balloon volume (BV) is corrected for the effect of the pressure in the patient's aorta. Comparison with dye dilution and thermal dilution procedures as carried out on a routine basis in a clinical setting produced a good correlation (r = .928). When fit to a straight line through zero output, the data yielded a constant of proportionality of 0.973 between the above formula and the clinical procedures. The procedure does not disturb the patient in any way, and enables continuous monitoring of cardiac output. This has been implemented using a real-time, miniaturized computer and allows much more information to be obtained than in usual single measurements.