Comparison of two methods for cardiac output measurement in critically ill patients

Background. The aim of recent haemodynamic monitoring has been to obtain continuous and reliable measures of cardiac output (CO) and indices of preload responsiveness. Many of these methods are based on the arterial pressure waveform analysis. The aim of our study was to assess the accuracy of CO measurements obtained by FloTrac/Vigileo, software version 1.07 and the new version 1.10 (Edwards Lifesciences LLC, Irvine, CA, USA), compared with CO measurements obtained by bolus thermodilution by pulmonary artery catheterization (PAC) in the intensive care setting. Methods. In 21 critically ill patients (enrolled in two University Hospitals), requiring invasive haemodynamic monitoring, PAC and FloTrac/Vigileo transducers connected to the arterial pressure line were placed. Simultaneous measurements of CO by two methods (FloTrac/ Vigileo and thermodilution) were obtained three times a day for 3 consecutive days, when possible. The level of concordance between the two methods was assessed by the procedure suggested by Bland and Altman. Results. One hundred and forty-one pairs of measurements (provided by thermodilution and by both 1.07 and 1.10 FloTrac/Vigileo versions) were obtained in 21 patients (seven of them were trauma patients) with a mean (SD) age of 59 (16) yr. The Pearson product moment coefficient was 0.62 (P,0.001). The bias was 20.18 litre min21. The limits of agreement were 4.54 and 24.90 litre min21, respectively. Conclusions. Our data show a poor level of concordance between measures provided by the two methods. We found an underestimation of CO values measured with the 1.07 software version of FloTrac for supranormal values of CO. The new software (1.10) has been improved in order to correct this bias; however, its reliability is still poor. On the basis of our data, we can therefore conclude that both software versions of FloTrac/Vigileo did not still provide reliable estimation of CO in our intensive care unit setting.