Early net ultrafiltration thresholds and mortality in critically ill patients with septic acute kidney injury receiving continuous renal replacement therapy

Net ultrafiltration (NUF) rates correlate with outcomes in critically ill patients on continuous renal replacement therapy (CRRT), but optimal strategies for septic acute kidney injury (AKI) are unclear. This study evaluated early NUF rates and survival in septic AKI. A retrospective cohort of 219 adults with septic AKI requiring CRRT at a tertiary ICU was analyzed. Early NUF (weight-adjusted fluid removal/hour during the first 48 h of CRRT) was stratified into low- (&lt;1.22 mL/kg/h), moderate- (1.22–1.79 mL/kg/h), and high-intensity (&gt;1.79 mL/kg/h) groups. The primary outcome was 28-day mortality. Associations were assessed using multivariable Cox regression and restricted cubic spline models, adjusted for demographics, severity scores, fluid balance, and biomarkers. The high-intensity group had the highest 28-day mortality (68.5% vs. 43.8% moderate vs. 45.2% low). High-intensity NUF was independently associated with increased mortality vs. moderate (adjusted HR = 1.88, 95% CI:1.19–2.97, <i>p</i> = 0.007) and low-intensity groups (adjusted HR = 2.01, 95% CI:1.25–3.22, <i>p</i> = 0.004). Nonlinear analysis demonstrated a nonlinear relationship, with risks escalating steeply at rates above 1.79 mL/kg/h. High-intensity NUF during early CRRT was associated with higher mortality in patients with septic AKI mortality, particularly among those with high severity of illness. Moderate NUF had lowest mortality, suggesting that intermediate NUF rates may best balance the competing risks of worsening hemodynamic instability from excess NUF and persistent volume overload from inadequate NUF. However, future trials are needed to better define the optimal approach to NUF in patients with septic AKI.