Abstract
OBJECTIVES: Net ultrafiltration (UF(net)) is widely used for fluid management during continuous renal replacement therapy (CRRT) for critically ill patients over extended periods. Despite widespread use, the relationship between UF(net) intensity and clinical outcomes, particularly mortality, remains controversial. METHODS: This retrospective observational study examined critically ill patients undergoing CRRT for more than 72 h from January 2021 to September 2023. Patients were stratified by their UF(net) intensity during the initial 72 h of CRRT into low (<1.01 mL/kg/h), moderate (1.01-1.75 mL/kg/h), and high (>1.75 mL/kg/h) groups. The primary outcome was 28-day mortality. Kaplan-Meier's survival curves with log-rank tests, Cox proportional hazards models, and propensity score matching were employed to assess the association between UF(net) intensity and mortality. RESULTS: A total of 683 patients were included. Compared with the moderate UF(net) intensity, the low UF(net) intensity (adjusted hazard ratio (HR) 1.54, 95%CI 1.24-1.91, p = .024) and high UF(net) intensity (adjusted HR 1.27, 95%CI 1.03-1.57, p < .001) were associated with higher 28-day mortality. Sensitivity analyses showed similar trends for 60-day and 90-day mortality. Subgroup analyses based on admission diagnosis did not reveal significant differences in the effect of UF(net) intensity on mortality risk. CONCLUSIONS: UF(net) intensity between 1.01 and 1.75 mL/kg/h during the first 72 h of CRRT was associated with lower 28-day mortality compared to both lower and higher UF(net) intensities. However, future studies are needed to better define optimal UF(net) thresholds in multicenter ICU cohorts.