Association between Net Ultrafiltration Intensity and Mortality in Patients with AKI Undergoing Low-Dose Continuous Kidney Replacement Therapy

Background: Continuous kidney replacement therapy (CKRT) is a preferred dialysis modality for hemodynamically unstable acute kidney injury (AKI) patients in the intensive care unit (ICU). Several retrospective studies have reported that a higher net ultrafiltration (UF) intensity is associated with better patient survival, under the standard KDIGO-recommended delivered CKRT dose of 20 to 25 mL/kg/h. In Japan, however, the CKRT doses are usually below the KDIGO recommendation due to government health insurance system restrictions, and the association between the net UF and the mortality under lower than the KDIGO-recommended delivered CKRT dose has remained unknown. Methods: We consecutively evaluated 603 patients who required CKRT in the ICU at Nara Medical University Hospital between January 1, 2012, and December 31, 2021. The following patients were excluded: those with end-stage kidney disease, deceased within 24 hours of ICU admission, CKRT for nonrenal indications, or CKRT duration exceeding 28 days. We categorized patients into four groups by median net UF intensity and delivered CKRT dose, and assessed ICU mortality using multivariable logistic regression. Results: Of the 603 patients, 494 were included in this study. The median net UF intensity was 3.7 mL/kg/day, and the delivered CKRT dose was 13.2 mL/kg/h. We categorized 494 patients into four groups based on median net UF intensity and delivered CKRT dose: 129 in low net UF intensity-low delivered CKRT dose, 118 in low-high, 118 in high-low, and 129 in high-high groups. The adjusted odds ratios (95% confidence intervals) for ICU mortality via multivariable logistic regression were as follows: low-low 1.54 (0.76–3.12); low-high 0.52 (0.23–1.20); high-low, reference; high-high 0.41 (0.19–0.90). Conclusion: In this cohort of AKI patients who underwent low-dose CKRT, higher net UF intensity with above-median delivered CKRT dose was independently associated with decreased ICU mortality, compared to higher net UF intensity with below-median delivered CKRT dose. These findings underscore the importance of optimizing CKRT dosing strategies in improving outcomes for AKI patients in the ICU.