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Acute kidney injury is the deterioration of renal function over hours or days resulting in the accumulation of toxic wastes and the loss of internal homeostasis. Definitions based on renal function are listed in Table 1.1

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Table 1 AKIN and RIFLE Criteria for Acute Kidney Injury
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Community- and hospital-acquired kidney injuries differ by cause, treatment, and outcome (Table 2). Community-acquired renal failure is diagnosed in only 1% of hospital admissions at the time of presentation2,3 and is usually secondary to volume depletion; thus, the vast majority of cases presenting to the ED have a reversible cause.3 Mortality among patients presenting to the ED with prerenal acute renal failure may be as low as 7%.4

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Table 2 Causes of Community-Acquired and Hospital-Acquired Acute Renal Failure
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Hospital-acquired renal failure is only apparent after admission.5 Hospital factors include advanced patient age, potential nephrotoxic exposures in a hospital setting, sepsis,6 and multiorgan system illness in hospitalized patients. There is an almost linear relationship between increasing severity of renal injury and mortality rate: no renal injury, 4.4%; risk category/stage 1, 15.1%; injury category/stage 2, 29.2%; and failure category/stage 3, 41.1%.6

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Renal insult is classified as prerenal (decreased perfusion of a normal kidney), intrinsic (pathologic change within the kidney itself), or postobstructive (obstruction to urine outflow).

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The functions of the kidneys are glomerular filtration, tubular reabsorption, and secretion. Normal glomerular filtration rate (GFR) in early adulthood is approximately 120 mL/min/1.73 m2 and typically decreases by 8 mL/min/1.73 m2 every decade thereafter. The driving force for glomerular filtration is glomerular capillary pressure, which depends on renal blood flow and autoregulation. For most ...

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