The prognostic impact of net ultrafiltration intensity in critically ill patients receiving continuous renal replacement therapy: a multivariable and propensity-matched analysis

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. 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 (&lt;1.01 mL/kg/h), moderate (1.01–1.75 mL/kg/h), and high (&gt;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. 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, <i>p</i> = .024) and high UF^net intensity (adjusted HR 1.27, 95%CI 1.03–1.57, <i>p</i> &lt; .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. 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.