Automated cardiac output measurements by ultrasound are inaccurate at highcardiac outputs

Objective The sonographic technique of automated cardiac output measurement (ACM) is a promising new method to measure cardiac output and could be of use in a high-risk obstetric unit in the treatment of pre-eclamptic patient s. The aim was to determine the accuracy of the ACM method. Design Comparative study of the sonographic technique of ACM versus cardiac output measured by thermodilution (TD). Methods The study included 39 intensive care patients, 21 men, 13 non-pregn ant women and five severely pre-eclamptic pregnant patients, with a wide ra nge of cardiac outputs, in whom TD catheters had been inserted for clinical reasons. Two separate experienced observers, blinded to the results obtain ed with the other method, performed four successive measurements in each pa tient with either the ACA-I or TD technique. The averaged cardiac output va lue per patient and method tons used for comparison. Results Cardiac output was successfully measured with ACM and TD in 85 and 100% of patients, respectively. Mean cardiac output measured by ACM (6.77 /- 1.90 L/min) was significantly lower than that measured by TD (9.12 +/- 3 .06 L/min). Although cardiac output values obtained with ACM were significa ntly correlated with those measured by TD, the ACM values were consistently lower than TD values in the higher cardiac output range; the relationship was represented by ACM = 0.35 TD + 3.55 L/min (r =0.57, P < 0.001). The (AC M - TD) difference increased significantly with cardiac output, through a d ifference in strobe volume, not in heart rate. Conclusion The ACM is not an accurate tool to measure cardiac output in pat ients with a high cardiac output, including treated pre-eclamptic women.