Editor's key points † Data are conflicting regarding the accuracy and validity of non-invasive cardiovascular monitoring devices in the critically ill. † This study compared changes in cardiac index in response to passive leg raising (PLR) and volume expansion using the NICOM w and PiCCO 2 TM devices. † There was poor correlation between the two monitors after volume expansion. † The NICOM w did not predict fluid responsiveness to PLR.Background. Bioreactance estimates cardiac output in a non-invasive way. We evaluated the ability of a bioreactance device (NICOM w ) to estimate cardiac index (CI) and to track relative changes induced by volume expansion.Methods. In 48 critically ill patients, we measured CI estimated by the NICOM w device (CI Nicom ) and by transpulmonary thermodilution (CI td , PiCCO 2 TM device) before and after a 500 ml saline infusion. Before volume expansion, we performed a passive leg raising (PLR) test and measured the changes it induced in CI Nicom and in pulse contour analysis-derived CI. Results.Considering the values recorded before PLR and before and after volume expansion (n¼144), the bias (lower and upper limits of agreement) between CI td and CI Nicom was 0.9 (22.2 to 4.1) litre min 21 m 22 . The percentage error was 82%. There was no significant correlation between the changes in CI td and CI Nicom induced by volume expansion (P¼0.24). An increase in CI estimated by pulse contour analysis .9% during the PLR test predicted fluid responsiveness with a sensitivity of 84% (95% confidence interval 60-97%) and a specificity of 97% (95% confidence interval 82-100%). The area under the receiver operating characteristic curve constructed to test the ability of the PLR-induced changes in CI Nicom in predicting fluid responsiveness did not differ significantly from 0.5 (P¼0.77).Conclusions. The NICOM w device cannot accurately estimate the cardiac output in critically ill patients. Moreover, it could not predict fluid responsiveness through the PLR test.

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