Severity of post-cardiac surgery acute kidney injury and long-term mortality: is chronic kidney disease the missing link?

Abstract

While the retrospective cohort study by Lopez-Delgado and colleagues suggests a strong association of the RIFLE classification and long-term mortality of acute kidney injury (AKI) after post-cardiac surgery, it has a number of limitations. The numbers of patients with pre-existing chronic kidney disease (CKD) or with non-recovery of renal function, de novo CKD or progression of CKD to stage V are not given. The authors used an obsolete definition of CKD and a modified RIFLE classification system for definition and grading of AKI. Taken together, numerous studies underscore the strong association between AKI and de novo CKD. Severity, duration and frequency of AKI as well as age, comorbidities and pre-existing CKD are known risk factors for the development and/or progression of CKD. Careful analyses of the cumulative mortality curves reported by Lopez-Delgado and colleagues or by our group revealed a triphasic pattern. In the early phase, survival rates drop steeply due to critical illness, followed by a phase of smaller decline (caused by patient characteristics and development of CKD) and later on by a flatter survival curve attributable to the high cardiovascular mortality of progressive CKD. Physicians need to consider the long-term sequels of severe AKI. Lopez Delgado and colleagues's study provides further arguments for an early follow-up of survivors of AKI by nephrologists.