Noninvasive cardiac output monitoring by aortic blood flow determination

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Abstract
The Sometec Dynemo-3000 system allows the permanent measurement of descending aorta diameter by an echographic (A-scan) device and the blood flow velocity by a pulse Doppler velocimeter. The Dynemo-3000 then furnishes a new hemodynamic parameter, i.e., desceding aortic blood flow (ABF), which is a fraction of the cardiac output (CO). We evaluate the ability of this system to measure the aortic diameter and to accurately detect ABF changes. A case study prospective trial. A 24-bed medical intensive care unit of a 1,100-bed university hospital. Twenty critically ill patients fully sedated, mechanically ventilated, and monitored by a pulmonary artery catheter. CO values determined by conventional thermodilution method (TD-CO) and ABF were recorded during the study, which included two initial baseline periods, a dobutamine infusion (5 [micro sign]g/kg/min) interval of 30 mins, and a third baseline period. To assess the accuracy of A-scan, aortic diameter was measured by transesophageal echocardiography. The difference between echocardiography and A-scan was used to determine bias and precision for aortic diameter measurements. TD-CO and ABF variations were analyzed using Kruskal-Wallis and Wilcoxon tests. Association between TD-CO and ABF values was determined by calculating the linear correlation coefficient. The ability of ABF to detect a TD-CO >6.0 L/min and its variations >13% was analyzed by determination of sensitivity, specificity, and positive (PPV) and negative (NPV) predictive values. Aortic diameter measurements by A-scan and bidimensional methods were 23.0 +/- 2.8 mm (SD) and 24.2 +/- 2.7 mm, respectively. Bias and precision were 1.1 mm and 1.4 mm (95% confidence interval: -1.9 to 3.7), respectively. During the course of dobutamine infusion, we observed a significant increase of TD-CO mean value from 6.65 +/- 1.53 L/min to 9.30 +/- 2.5 L/min (p = .0008), and a parallel and significant increase in ABF mean value from 4.34 +/- 1.18 L/min to 5.70 +/- 1.63 L/min (p = .0029). Absolute TD-CO and ABF values had a correlation coefficient of 0.80. For detection of an increased TD-CO, PPV and NPV were 87% and 86%, respectively. For detection of TD-CO changes >13%, PPV and NPV were 80% and 94%, respectively. The Dynemo-3000 system is able to display the real aortic diameter, which is one of the most important components of this noninvasive ultrasonic technique. When compared with TD-CO, the ABF determination provided by this ultrasonic device constitutes a reliable noninvasive tool for estimating CO and tracking its changes. (Crit Care Med 1998; 26:2066-2072)