Acute kidney injury after cardiac surgery: A comparison of different definitions

Acute kidney injury (AKI) after cardiac surgery increases morbidity and mortality. Different definitions for AKI have been used such as Acute Kidney Injury Network (AKIN), Kidney Disease: Improving Global Outcomes (KDIGO) or risk, injury, failure, loss, end-stage kidney disease (RIFLE). The aim of this study is to determine the best definition of AKI after cardiac surgery with the largest impact on the outcome.

This retrospective study of cardiac surgery patients compared the incidence and effect on outcome (90-day and 1-year mortality) of different definitions of AKI: RIFLE, AKIN and KDIGO. Additionally, we defined transient AKI (increase in serum creatinine that resolved in <72 hours), sustained (increase in serum creatinine within 48 hours that remained for >72 hours), and late (increase in serum creatinine after 48 hours).

Of the included 1551 patients, 410 patients developed AKI defined by AKIN criteria, 449 defined by KDIGO and 217 defined by RIFLE-Risk criteria. Hundred and nine patients developed transient AKI (6.9%), 183 patients had sustained AKI (11.6%), and 106 patients had late AKI (6.7%). The best definition with the highest positive likelihood ratio was RIFLE-Risk (positive likelihood ratio = 2.32) followed by "sustained AKI" (positive likelihood ratio = 2.27). AKI defined by AKIN criteria missed all 80 patients with late AKI and 39 patients with KDIGO AKI.

Risk, injury, failure, loss, end-stage kidney disease-risk was the best definition of AKI as determined by the ability to predict short-term mortality. A substantial number of patients developed AKI only after 48 hours, and these were missed when using AKIN criteria. AKIN criteria are not sensitive enough to capture all episodes of AKI in this population.