Relationship between urine output and 28-day mortality in patients with acute kidney injury receiving continuous renal replacement therapy

BACKGROUND: Most critically ill patients with acute kidney injury (AKI) can be controlled with continuous renal replacement therapy (CRRT), but the timing of CRRT initiation is debatable and there is no specific indication. The aim of this study was to investigate whether there is a correlation between different urine output levels at the start of CRRT and the prognosis of critically ill patients with AKI who require CRRT. METHODS: This was a secondary analysis that retrieved the clinical, biochemical, and 28-day mortality rates of critically ill AKI patients who required CRRT from 2009 to 2016, and grouped the patients into two groups of patients with 2-hour urine output at the start of CRRT, and explored the effect of urine output at the onset of CRRT on 28-day all-cause mortality through univariate, multivariate, Kaplan-Meier curves, and subgroup analyses. RESULTS: A total of 1138 participants were enrolled in this study. Multivariate Cox proportional hazards regression analysis showed a significantly lower 28-day risk of death in the non-oliguria group compared with the oliguria group after fully adjusting for confounding variables (P = 0.0014), with an adjusted hazard ratio (95% confidence interval) of 0.75 (0.63–0.89). Subgroup analyses showed that oliguria and an increased risk of 28-day mortality were associated in patients requiring CRRT due to hyperkalemia and AKI due to sepsis, but this result was not found in patients with other indications for CRRT and other causes of AKI. CONCLUSION: Oliguria is associated with an increased risk of 28-day mortality in critically ill AKI patients requiring CRRT, especially in patients requiring CRRT due to hyperkalemia, and in patients with AKI due to sepsis. CLINICAL TRIAL NUMBER: Not applicable.