Does the definition of fluid responsiveness affect passive leg raising reliability? A methodological ancillary analysis from a multicentric study

BACKGROUND: Fluid challenge (FC) is often adopted as gold standard used to assess the reliability of passive leg rais-ing (PLR) in predicting fluid responsiveness in the intensive care unit (ICU). This study aimed to address the impact of the different definitions and timings used to assess FC response on PLR reliability. METHODS: Ancillary study from a data set of a multicentric study in 85 ICU patient with acute circulatory failure who received a FC (500 mL of crystalloids in 10 minutes) within the first 48h of ICU admission, preceded by PLR in 30 patients. FC response was assessed considering the changes in Cardiac Index (CI) and Stroke Volume Index (SVI) using different thresholds and at different time-points. RESULTS: The definitions of fluid responsiveness by using CI or SVI with a 15% increase after 10 minutes were as-sociated to the best performances of the PLR (AUC 0.94 [95% CI 0.83-1.01] vs. AUC 0.95 [95% CI 0.87-1.02]). The sensitivity of the PLR by adopting the CI or the SVI as reference variable ranged from 54.1% to 67.6% and from 81.5% to 100.0%; the specificity from 65.9% to 78.0% and from 79.5% to 100.0%, respectively. Considering all the subgroups, the number of responders 10 minutes after FC administration was higher as compared to 15 and 30 minutes (140 vs. 120 and 125, respectively, P<0.05). CONCLUSIONS: The reliability of the PLR test to predict fluid responsiveness depends on the definition of FC adopted. The timing of FC outcome assessment affected the overall fluid responsiveness.