AKI may develop in a wide variety o

AKI may develop in a wide variety of settings, including
in ambulatory outpatients, hospitalized patients, and,
in particular, critically ill patients, for whom AKI represents
a common complication of both underlying disease
and treatment.AKI is associated with substantial morbidity
and mortality. For example, severe AKI occurs in

5% of critically ill patients and is associated with
mortality rates of 40%-70%.10-12 Although recovery of
kidney function occurs in the majority of patients surviving
an episode of AKI, many patients remain dialysis
dependent or are left with severe renal impairment. More
recently, it has been recognized that even patients who
have complete or near-complete recovery of kidney
function are at increased risk of progressive chronic
kidney disease (CKD) and that superimposition of AKI
on CKD is associated with acceleration in the rate of
progression to end-stage disease.13-17
Our understanding of the epidemiology of AKI and
interpretation of results across clinical trials has been
hindered by the prior absence of a broadly accepted
clinical definition, with more than 30 operational
definitions of AKI used in published studies.18 During
the past decade, there has been a considerable effort to
forge a consensus definition. The first attempt at
developing a consensus definition, known as the
RIFLE criteria, was developed by the Acute Dialysis
Quality Initiative (ADQI) in 2002 (Table 1).19 This
definition considered 3 strata of severity (risk, injury,
and failure) based on the magnitude of increase in
serum creatinine level and/or the duration of oliguria,
as well as 2 outcome stages (loss of kidney function
and end-stage kidney disease). The risk, injury, and
failure categories were constructed to provide gradations
in severity of kidney dysfunction, with greater
sensitivity associated with risk and greater specificity
with failure. The RIFLE criteria subsequently were
modified by the AKI Network (AKIN) by the addition
of an absolute increase in serum creatinine level
0.3