RIFLE criteria for assessing AKI (Acute Kidney Injury)

Acute Kidney Injury (AKI) affects 5 to 7% of all hospitalized patients. In the ICU population, this syndrome is common with an incidence of 1 to 25%, depending on the criteria used for definition, and is associated with mortality rates of 50 to 70% . For many decades, diverse definitions for AKI have been used, which explains the difficulty in understanding the wide inter-study variations. AKI is a complex disorder with multiple etiologies, different clinical manifestations, and outcomes ranging from minimal elevation in serum creatinine to anuric renal failure.

In response to the need for a common meaning for AKI, because AKI has been, over the last few decades the focus of extensive clinical research efforts, the Acute Dialysis Quality Initiative Group, a panel of international experts in nephrology and critical care medicine, developed and published a set of consensus criteria for a uniform definition and classification of AKI . These criteria, which make up the acronym 'RIFLE', classify renal dysfunction according to the degree of impairment present: there are three grades of severity - risk (R), injury (I), and failure (F), and two outcome classes - sustained loss (L) of kidney function and end-stage kidney disease (E). RIFLE criteria, which have the advantage of providing diagnostic definitions for a stage when kidney injury can still be prevented (R), have been tested in clinical practice and seem to be at least congruent with the outcome of a patient with AKI .This system has several advantages. It appears sensitive to the early changes in kidney function, allows monitoring of progression of AKI and could function as a robust instrument to discriminate clinical relevant outcomes. The RIFLE classification has been evaluated and validated in numerous clinical studies enrolling critically ill patients namely post-operative patients and burned patients, and found to be a valid tool for the precocity of the diagnosis and staging of AKI, having predictive ability for mortality . A few studies in trauma patients have shown that the incidence of renal failure varies from less than 0.1% to 18%, with an associated mortality ranging from 7 to 83%. In particular, the study by Bagshaw and a study by Yuan were able to show the application of the RIFLE criteria to characterize AKI in a population of patients with trauma.

Keeping in mind the relevance of this issue and the limited data available in the literature, we aimed to characterize AKI using the RIFLE classification and relate it to ICU length of stay (LOS), hospital LOS, and mortality in a cohort of severe trauma patients that needed Intensive Care. Preliminary results of this study were published elsewhere.

Patients were classified into classes R (Risk), I (Injury) and F (Failure), according to the highest RIFLE class reached during their ICU stay. The RIFLE class was determined according to the worst degree of either glomerular filtration rate (GFR) criteria (according to the creatinine values and never used the GFR per se) or urine output criteria. For patients without serum creatinine baseline historical data, we determined a baseline serum creatinine level using the Modification of Diet in Renal Disease equation (MDRD) . When baseline serum creatinine is unknown, current recommendations allow you to estimate this value using the MDRD equation, assuming a glomerular filtration ratio of 75 ml/min/1.73 m2. Recently, Bagshaw and collaborators validated the use of this equation to assess RIFLE criteria .

We measured outcomes as the use of renal replacement therapy, length of ICU and hospital stay, and mortality. We divided mortality into ICU mortality, if it occurred during ICU stay and Hospital mortality if it occurred during the rest of Hospital stay. If mortality occurred after hospital discharge it was not considered. Moreover we divided mortality into early (2 or less days) and late (more than 2 days).