The causes of ARF can be classified as prerenal, intrarenal (intrinsic), and postrenal. Prerenal ARF results from conditions that cause diminished blood flow to the kidneys. Disorders that can lead to prerenal failure include cardiovascular disorders (dysrhythmias, cardiogenic shock, congestive heart failure, myocardial infarction), disorders that cause hypovolemia (burns, trauma, dehydration, hemorrhage), maldistribution of blood (septic shock, anaphylactic shock), renal artery obstruction, and severe vasoconstriction.

Intrarenal, or intrinsic, ARF involves the actual destruction of the renal parenchyma (functional cells). The most common cause of intrarenal failure is acute tubular necrosis, or damage to the renal tubules because of either a nephrotoxic or an ischemic injury. Nephro-toxic injuries occur when the renal tubules are exposed to a high concentration of a toxic chemical. Common sources of nephrotoxic injuries include antibiotics (aminoglycosides, sulfonamides), diuretics, nonsteroidal anti-inflammatory drugs (ibuprofen), and contrast

806 Renal Failure, Acute media from diagnostic tests. Ischemic injuries occur when the mean arterial blood pressure is less than 60 mm Hg for 40 to 60 minutes. Situations that can lead to ischemic injuries include cardiopulmonary arrest, hypovolemic or hemorrhagic shock, cardiogenic shock, or severe hypotension.

Postrenal (postobstructive) ARF is caused by a blockage to urine outflow. One of the most common causes of postrenal ARF in hospitalized patients is an obstructed Foley catheter. Other conditions that can lead to postrenal ARF include ureteral inflammation or obstruction, accidental ligation of the ureters, bladder obstruction (infection, anticholinergic drug use, tumors, trauma leading to bladder rupture), or urethral obstruction (prostate enlargement, urethral trauma, urethral strictures).

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