Introduction: The Acute Kidney Injury Network proposed a new classification for acute kidney injury (AKI) distinguishing between three stages. We applied the criteria to a large intensive care unit (ICU) population and evaluated the impact of AKI in the context of other risk factors.
Methods: Using the Riyadh Intensive Care Program database, we applied the AKI classification to 22,303 adult patients admitted to 22 ICUs in the UK and Germany between 1989 and 1999, who stayed in the ICU for 24 hours or longer and did not have end-stage dialysis dependent renal failure.
Results: Of the patients, 7898 (35.4%) fulfilled the criteria for AKI (19.1% had AKI I 3.8% had AKI II and 12.5% had AKI III). Mortality in the ICU was 10.7% in patients with no AKI, 20.1% in AKI I, 25.9% in AKI II and 49.6% in AKI III. Multivariate analysis confirmed that AKI III, but not AKI I and AKI II, were independently associated with ICU mortality (odds ratio (OR) = 2.27). Other independent risk factors for ICU mortality were age (OR = 1.03), sequential organ failure assessment (SOFA) score on admission to the ICU (OR = 1.11), pre-existing end-stage chronic health (OR = 1.65), emergency surgery (OR = 2.33), mechanical ventilation (OR = 2.83), maximum number of failed organ systems (OR = 2.80) and non-surgical admission (OR = 3.57). Cardiac surgery, AKI I and renal replacement therapy were associated with a reduced risk of dying in the ICU. AKI II was not an independent risk factor for ICU mortality. Without renal replacement therapy as a criterion, 21% of patients classified as AKI III would have been classified as AKI II or AKI I. Renal replacement therapy as a criterion for AKI III may inadvertently diminish the predictive power of the classification.
Conclusions: The proposed AKI classification correlated with ICU outcome but only AKI III was an independent risk factor for ICU mortality. The use of renal replacement therapy as a criterion for AKI III may have a confounding effect on the predictive power of the classification system as a whole.