Our paper 20 years later: from acute renal failure to acute kidney injury--the metamorphosis of a syndrome.

PURPOSE: More than 20 years ago we reported an analysis of a case series of elderly critically ill patients with acute kidney injury (AKI)--then termed acute renal failure. At that time, AKI was regarded as a "simple" complication, but has since undergone a fundamental change and actually has become one of the central syndromes in the critically ill patient.

METHODS: We have analyzed elderly patients above 65 years of age with an AKI defined as serum creatinine above 3 mg/dl corresponding to modern KDIGO stage 3, most of them requiring renal replacement therapy (RRT). Using an extremely complete data set the diagnosis differentiated the underlying disease entity, the dominant cause of AKI, acute and chronic risk factors (comorbidities). Special aspects such as severity of disease, early AKI at admission versus late AKI, early versus later start of RRT, AKI not treated by RRT in spite of indication for RRT, various measures of short-term and long-term prognosis, renal outcome, patients dying with resolved AKI, and causes of death were evaluated.

RESULTS: Crude mortality was 61% which corresponds to modern studies with gross variation among the different subgroups. Age per se was not a determinant of survival either within the group of elderly patients or as compared to younger age groups. Despite an increase in mean age and disease severity during the observation period prognosis improved. A total of 17% of patients developed a chronic kidney disease. Long-term survival as compared to the general population was low.

CONCLUSIONS: A look back at the last two decades illustrates a remarkable evolution or rather metamorphosis of a syndrome. AKI has evolved as a central syndrome in intensive care patients, a systemic disease process associated with multiple systemic sequels and extra-renal organ injury and exerting a pronounced effect on the course of disease and short- and long-term prognosis not only of the patient but also of the kidney. Moreover, the "non-renal-naïve" elderly patient with multiple comorbidities has become the most frequent ICU patient in industrialized nations.