Mortality of patients with acute kidney injury requiring renal replacement therapy

Background. Acute kidney injury (AKI) in critically ill patients has a deleterious impact on the prognosis, especially when renal replacement therapy (RRT) is required. This issue has not yet been investigated in the intensive care setting in Poland. Objectives. The aim of the study was to evaluate the short-term outcomes of AKI-RRT subjects, based on a large registry population. Material and methods. This observational multicenter study covered 100 demographic and clinical variables from the Silesian Registry of ICUs regarding 15,030 adult patients hospitalized between October 2011 and December 2014. The study group comprised 1,234 AKI individuals (8.2%) who required RRT. The primary outcome was ICU mortality. The length of ICU stay (LOS) was considered the secondary outcome. Observed mortality was compared to that predicted by the Acute Physiology and Chronic Health Evaluation II (APACHE II). Results. The overall mortality of the patients in the registry was 43.9%; it was higher in AKI-RRT subjects than in non-AKI-RRT counterparts (69.4% vs 41.0%; p < 0.01). The median APACHE II score among AKI-RRT subjects was 26 (IQR: 20-32) points. The observed mortality among AKI-RRT patients was significantly higher than predicted by APACHE II, particularly in individuals with lower baseline risk (overall difference: 14.4%). Six patient-related variables independently predicted ICU mortality with moderate accuracy (area under the receiver operating characteristic, AUROC = 0.675; 95% CI 0.65-0.70). The ICU LOS of AKI-RRT subjects was longer than that of the controls (9.8 [IQR: 4.0-19] vs 5.7 [IQR: 2.1-12] days; p < 0.001). Conclusions. The mortality of critically ill AKI patients requiring RRT was significantly higher than in the overall ICU population. APACHE II scores underestimate mortality, especially in low-risk AKI-RRT subjects, and therefore should not be used in prognostic models in this cohort.