0071643192.pdf

RENAL AND GENITOURINARY

EMERGENCIES

Prerenal

Prerenal acute renal failure occurs as a result of decreased renal perfusion. It is

the most common reason for acute renal failure in the nonhospitalized patient.

CAUSES

Causes of prerenal ARF include:

■ Hypovolemia: Hemorrhage, vomiting and diarrhea, diuretic therapy

■ Volume redistribution: Third-space sequestration, sepsis, hypoalbuminemic

states

■ Decreased effective cardiac output: Myocardial infarction, valvular disease,

cardiomyopathy

■ Medications that limit glomerular perfusion: ACE inhibitor or prostaglandin

(NSAID) use

SYMPTOMS/EXAM

Will vary depending on underlying etiology

TABLE 18.3. Classification and Causes of Acute Renal Failure

PRERENAL INTRINSICRENAL POSTRENAL

Hypovolemia Glomerulonephritis Urinary tract obstruction

Volume redistribution Acute interstitial nephritis (AIN) (at any level)

Decreased effective Acute tubular necrosis (ATN)

cardiac output Vascular causes

Medications

The primary cause of

community-acquired acute

renal failure is hypovolemia.

Suspect bilateral renal artery

stenosis in patients with acute

renal failure after initiating

ACE inhibitor therapy.

Prerenal acute renal failure is

associated with a low UNa

(<20 mEq/dL) and a low FENa

(<1%).

TABLE 18.4. Urinary Indices in Acute Renal Failure

INTRINSICRENAL

ACUTE ACUTE

ACUTETUBULAR GLOMERULONE INTERSTITIAL

PRERENAL NECROSIS PHRITIS NEPHRITIS POSTRENAL

Serum BUN/Cr >20:1 <20:1 >20:1 <20:1 >20:1

ratio

UNa(mEq/L) <20 >20 <20 Variable Variable

FENa(%) <1 >2 <1 Variable Variable

Urine osmolality Increased <350 Increased Variable < 350

Urinalysis Normal or Granular Dysmorphic WBC, WBC Normal

hyaline casts (muddy brown) RBCs, RBC casts, casts,

casts, renal proteinuria eosinophils

tubular casts