Distensibility index of the inferior vena cava in experimental acute respiratory distress syndrome

We determined the accuracy of distensibility index of inferior vena cava (dIVC) for evaluation of fluid responsiveness in rats with acute respiratory distress syndrome (ARDS) and validated this index for use in rat models. In protocol 1, E. coli lipopolysaccharide was administered in Wistar rats (n=7). After 24h, animals were mechanically ventilated, and stroke volume (SV) and dIVC quantified after blood drainage and subsequent volume expansion (albumin 20%). A receiver operating characteristic (ROC) curve was plotted to determine the optimal dIVC cutoff. In protocol 2, rats (n=10) were divided into fluid-responders (SV increase >5%) and nonresponders (SV increase <5%). The dIVC cutoff obtained from protocol 1 was 25%. Fluid responders had a 2.5 relative risk of low dIVC (<25%). The sensitivity, specificity, positive predictive, and negative predictive values for dIVC were 74%, 62%, 59%, and 76%, respectively. In conclusion, a dIVC threshold <25% was associated with positive response after volume expansion and could be used to titrate fluids in endotoxin-induced ARDS.