The estimation of cardiac output by the Nexfin device is of poor reliability for tracking the effects of a fluid challenge

INTRODUCTION: The Nexfin device estimates arterial pressure by the volume clamp method through a finger pneumatic cuff. It also allows to estimate cardiac index (CI(noninv)) by pulse contour analysis of the non-invasive arterial pressure curve. We evaluated the ability of the device to track changes in cardiac index induced by a fluid challenge. METHODS: We included 45 patients for whom a volume expansion (500 mL of saline infused over 30 min) was planned. The volume expansion-induced changes in cardiac index measured by transpulmonary thermodilution (CI(inv), PiCCO device) and in CI(noninv )were recorded. RESULTS: In seven patients, the Nexfin could not record the arterial curve due to finger hypoperfusion. Considering both the values obtained before and after volume expansion (n = 76 pairs of measurements), the bias (lower and upper limits of agreement) between CI(inv )and CI(noninv )was 0.2 (-1.8 to 2.2) L/min/m(2). The mean change in CI(noninv )was 10 ± 11%. The percentage error of CI(noninv )was 57%. The correlation between the changes in CI(inv )and CI(noninv )observed during volume expansion was significant (P = 0.0002) with an r(2 )= 0.31. CONCLUSIONS: The estimation of CI by the Nexfin device in critically ill patients is not reliable, neither for estimating absolute values of CI nor for tracking its changes during volume expansion.