Acute Kidney Injury and Kidney Replacement Therapy in the Critically Ill Patient

Acute kidney injury (AKI), previously known as acute renal failure, is an acute decline in kidney function

that occurs over hours to days and encompasses the full continuum of kidney injury and functional

impairment.

and fluid retention.

AKI has been associated with increased mortality, development of chronic kidney disease (CKD),

cardiovascular complications, and end-stage renal disease.

AKI is a heterogeneous syndrome with multiple causes and associated pathophysiologic mechanisms.

The true incidence of AKI varies and depends on the definition used, its cause, and the patient population

(e.g., community- or hospital-acquired and severity of illness).

(bites), and pregnancy. Other causes include HIV infection, hantavirus infection, and malaria or dengue

disease. These patients are more often younger and previously healthy and have more difficult access

to care.

Hospital-acquired AKI occurs infrequently in patients with less severe illness admitted to a general

hospital ward (1.9%–20%). In critically ill patients, the risk is greater, occurring in 20%–67% of patients.

Sepsis and shock are common causes of acute tubular necrosis (ATN), which is a leading phenotype of

AKI in critical illness. Other risk factors for AKI include use of intravenous radiocontrast agents, major

surgery (especially cardiothoracic), nephrotoxic medications, and chronic medical conditions (e.g.,

history of CKD, congestive heart failure, and diabetes). Most patients have more than one risk factor.

Mortality rates in patients with AKI are 10%–80%, with the highest in patients with multisystem organ

failure (50%) and those requiring kidney replacement therapy (KRT) (up to 80%).

Females tend to be underrepresented in the reported incidence of AKI, accounting for only 40% of

cases, which may be related to limited access to healthcare in women or sex-related risks for AKI

development in males. Ethnic and racial differences are less well described. A cohort study in the United

States found socioeconomic status to account for higher risk of AKI in African American individuals

compared with white individuals.

During the past several decades, many definitions have been used for AKI, making it difficult to compare

patient populations across studies. In 2004, the Acute Dialysis Quality Initiative workgroup developed

the RIFLE (risk, injury, failure, loss, end-stage renal disease) definition and staging system.

RIFLE categorizes AKI into three grades of increasing severity (risk, injury, and failure) and two

clinical outcomes (loss and end-stage).

Staging is based on the degree of SCr increase or a decrease in glomerular filtration rate over 7 days,

or the duration of oliguria or anuria.

in 2007 the Acute Kidney Injury Network (AKIN) criteria was developed.

Similar to RIFLE, this group defined AKI using a staging system of 1-3, defined by a reduction in

kidney function over no more than 48 hours using measures of SCr, urinary output (UOP), and need

for KRT.