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Chapter 88: Acute Kidney Injury

Richard Sinert; Peter R. Peacock, Jr.

INTRODUCTION AND EPIDEMIOLOGY

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 88-1.1

TABLE 88-1AKIN and RIFLE Criteria for Acute Kidney Injury
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TABLE 88-1 AKIN and RIFLE Criteria for Acute Kidney Injury
AKIN Stage RIFLE Category GFR Criteria Urine Output Criteria
Stage 1 Risk

Serum Cr increased 1.5 times*

or (AKIN only)

Cr increase >0.3 milligrams/dL over <48 h*

or

GFR decrease 25%–50%*

 0.5 mL/kg/h for 6 h
Stage 2 Injury

Serum Cr increased 2.0–3.0 times*

or

GFR decrease 50%–75%*

 0.5 mL/kg/h for 12 h
Stage 3 Failure

Serum Cr increased >3.0 times*

or

Cr >4 milligrams/dL and acute increase >0.5 milligrams/dL*

or

GFR decrease >75%*

0.3 mL/kg/h for 24 h

or

Anuria for 12 h
N/A Loss Complete loss of kidney function for >4 wk
End-stage renal disease Need for renal replacement therapy for >3 months

Abbreviations: AKIN = Acute Kidney Injury Network; Cr = creatinine; GFR = glomerular filtration rate; N/A = not applicable; RIFLE = Risk, Injury, Failure, Loss, End Stage.

*All changes are relative to the patient's premorbid baseline.

Community- and hospital-acquired kidney injuries differ by cause, treatment, and outcome (Table 88-2). 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

TABLE 88-2Causes of Community-Acquired and Hospital-Acquired Acute Renal Failure
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TABLE 88-2 Causes of Community-Acquired and Hospital-Acquired Acute Renal Failure
Community Acquired Hospital Acquired
Prerenal 70% Prerenal 20%
Intrinsic 20% Acute tubular necrosis 70%
Postrenal 10% Postrenal 10%

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

PATHOPHYSIOLOGY

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).

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 ...

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