Abstract: Objective  To investigate the relationship between net ultrafiltration rate (UFNET) and prognosis of the patients with acute kidney injury (AKI) receiving continuous renal replacement therapy (CRRT) based on the propensity score matching method (PSM).  Methods  Clinical data of 162 AKI patients treated with CRRT in The First People's Hospital of Lanzhou from February 2020 to February 2024 were retrospectively analyzed. The survival rate within 28 days of hospitalization was analyzed. UFNET value was recorded during CRRT. Receiver operating characteristic (ROC) curve was used to determine the cut-off UFNET value to predict death within 28 days of hospitalization in AKI patients receiving CRRT. PSM was used to balance the confounding factors between high UFNET group and low UFNET group, and the mortality rate within 28 days of hospitalization after PSM was compared by 1:1 matching. Univariate Cox regression was used to analyze the relationship between UFNET and 28-day death in AKI patients receiving CRRT.   Results  Among the 162 AKI patients treated with CRRT, 68 (41.98%) died within 28 days in hospital. The cut-off UFNET value to predict the death rate within 28 days of hospitalization in AKI patients was 1.51 ml/(kg·h).  Patients were divided into high UFNET group (78 cases) and low UFNET group (84 cases) according to the cut-off UFNET value. Before PSM, the proportion of patients with the Acute Kidney Injury stage Ⅲ (57.69% vs. 38.10%), the Oxford Acute Severity of Illness Score (OASIS) at admission (49.35±6.09 points vs. 45.02±5.71 points), the Sequential Organ Failure Assessment Score (SOFA) at admission (13.65±2.04 points vs. 10.08±2.14 points), the proportion of patients receiving mechanical ventilation (57.69% vs. 41.67%), the highest level of blood urea nitrogen (BUN) [(16.35±3.02)mmol/L vs. (13.09±2.61)mmol/L] and the highest level of serum creatinine (Scr) [(109.33±6.21）μmol/L vs. (101.12±5.09)μmol/L] were significantly higher in high UFNET group than in low UFNET group (t/χ²=6.228, 4.671, 10.850, 8.414, 7.366 and 9.253 respectively; P=0.013, 0.000, 0.000, 0.004, 0.000 and 0.000 respectively), while the lowest pH value (7.20±0.16 vs. 7.33±0.19), the lowest base excess [(-10.32±2.41)mmol/L vs. (-6.32±1.59)mmol/L] and the lowest estimated glomerular filtration rate (eGFR) [(60.34±6.09 ml/(min·1.73m²) vs. 66.75±7.82 ml/(min·1.73m²)] were significantly lower in high UFNET group than in low UFNET group (t=4.692, 12.553 and 5.790 respectively; P=0.000, 0.000 and 0.000 respectively). PSM matched 92 AKI patients, and the distribution of variables reached equilibrium between the two groups after PSM (P>0.05); the 28 day in-hospital mortality was higher in high UFNET group than in low UFNET group (52.17% vs. 26.09%; log-rank: χ²=6.324, P=0.000). Univariate COX regression analysis showed that the risk of 28 day in-hospital death in high UFNET group was 2.123 times higher than that in low UFNET group (HR=2.123, 95% CI: 1.152～3.914, P=0.000).   Conclusion   High UFNET is associated with death within 28 days of hospitalization in AKI patients receiving CRRT.

Key words: Acute kidney injury, Continuous renal replacement therapy, Fluid overload, Net ultrafiltration