Long-term survival for ICU patients with acute kidney injury

Introduction

A recently published study [1] validated the criteria used in the Acute Kidney Injury Network (AKIN) definitions [2] of the three stages of acute kidney injury (AKI) using in-hospital mortality. In the present study, we validate the clinical applicability of the AKIN classifications through long-term survival analysis of AKI patients.

Methods

From over 17,000 adult ICU patients in the MIMIC II database [3, 4] (V2.5), we excluded patients having end-stage renal disease and those with insufficient data and determined AKI stages for each patient. Multivariate Cox regression was used to determine hazard ratios (HRs) for 2-year survival, controlling for: age, sex, nonrenal Sequential Organ Failure Assessment (SOFA) score and selected co-morbidities.

Results

Among the final cohort of 14,525 patients, 43% had no AKI and 39%, 14% and 4% developed AKI 1, 2 and 3 respectively. The results of the regression analysis show that AKI 1 (HR 1.12, P < 0.05), AKI 2 (HR 1.10, P = 0.05) and AKI 3 (HR 1.64, P < 0.001) were significantly associated with increased 2-year mortality. In addition, age (HR 1.04, P < 0.001), gender (M) (HR 0.93, P < 0.05), nonrenal SOFA score (HR 1.05, P < 0.001) and all co-morbidities were significant predictors. Adjusted and unadjusted Kaplan-Meier curves for patients with AKI 3 are remarkably different from each other, suggesting that in these most severely ill patients AKI is only one aspect of their illness.

Conclusion

AKI stages 1, 2 and 3 are significant indicators of 2-year mortality. The difference between AKI 1 and 2 is smaller than that between AKI 2 and 3 and it may be prudent to re-examine the criteria used to define AKI to provide better separation among the three classes.