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

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.

Keywords: Net ultrafiltration; acute kidney injury; continuous renal replacement therapy; fluid overload.

Graphical abstract

Figure 1.

The association of UF^net intensity and risk of 28-day mortality. The association was plotted using a multivariate generalized additive linear model, which accounts for age, gender, body mass index, diagnosis, baseline serum creatinine, mean arterial pressure before CRRT, lactate before CRRT, oxygenation index before CRRT, sequential organ failure assessment score before CRRT, Acute Physiology and Chronic Health Evaluation II score before CRRT, oliguria before CRRT, the percent of patients with FO >5% before CRRT, and cumulative fluid overload percent in the first 24 h of CRRT.

Figure 2.

Flowchart of study selection.

Figure 3.

Kaplan–Meier’s survival plots with the log-rank test by different UF^net intensity categories in the first 72 h.