Time-Dependent Fluid Accumulation Index for Phase-Specific Risk Stratification in Septic Shock with Heart Failure

Fluid management in patients with septic shock and coexisting heart failure is a critical challenge, as it requires balancing resuscitation and the risk of fluid overload. This study investigated the potential of the fluid accumulation index (FAI), which is measured serially during the initial 72 h of intensive care unit (ICU) care, to provide dynamic prognostic information to guide fluid management in this high-risk population.

Restricted cubic spline (RCS) analysis was used to explore the relationships between FAI levels at different time points within 72 h of ICU admission and ICU mortality. Associations were quantified via multivariate Cox proportional hazards models. Subgroup analyses and Kaplan‒Meier survival curves were used to evaluate the consistency of associations and differences in survival between groups.

A total of 643 patients with septic shock and concurrent heart failure were included, among whom 127 died. The RCS revealed a significant nonlinear relationship between FAI levels at various time points and ICU mortality. The optimal FAI cutoff values decreased over time: the cumulative values were 0.87 at 24 h, 0.59 at 48 h, and 0.56 at 72 h. The cutoff values for specific intervals were 0.27 for the 24-48 h period (2-24 h-FAI) and 0.12 for the 48-72 h period (3-24 h-FAI). In the fully adjusted model, FAI values exceeding these time-specific thresholds were significantly associated with increased ICU mortality (24 h-FAI > 0.87, HR = 1.96, P = 0.0251; 2-24 h-FAI > 0.27, HR = 2.07, P = 0.0051; 48 h-FAI > 0.59, HR = 2.50, P = 0.0005; 3-24 h-FAI > 0.12, HR = 2.05, P = 0.0091; 72 h-FAI > 0.56, HR = 2.97, P < 0.0001). These associations remained consistent across most predefined subgroups.

FAI serves as a dynamic and independent prognostic marker for critically ill patients with septic shock and heart failure during the first 72 h of ICU admission. A key finding was the time-dependent decline in the optimal FAI cutoff values (0.87 at 24 h vs. 0.12 for the 3-24 h period). This temporal decline supports a shift in fluid management strategy from an initial liberal approach toward a conservative strategy after the first 24 h, which may mitigate mortality risk.