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