Thrombotic occlusive renal artery disease often complicates severe aortic and renal arterial atherosclerosis, especially when renal blood flow is reduced because of heart failure or volume depletion. Symptoms of renal artery occlusion may be notably absent. If renal function previously was good, the only manifestation of unilateral thrombosis may be an increase in BUN and serum creatinine levels and perhaps a modest increase in blood pressure. In patients with preexisting renal impairment ami azotemia, renal artery occlusion may precipitate heart failure, marked hypertension, and the uremic syndrome.
Renal scanning is usually more informative than IV urography in evaluating a patient with possible renal artery thrombosis. It is also safer. However, definitive diagnosis requires angiography. A coexisting abdominal aortic aneurysm should be sought, because it may lead to renal artery occlusion by extension of atheroma or dissection. In angiography, the least possible amount of contrast material should be used to minimize the likelihood of a nephrotoxic reaction; such a reaction. while generally limited to several days of oliguria and mild azotemia, may take the form of acute oliguric renal failure.
When technically feasible, surgical revascularization should be considered. Prompt revascularization can lead lo a substantial return of renal function, and some patients recover even if surgery is delayed several months.
ACUTE RENAL FAILURE
The clinical conditions associated with rapid, steadily increasing azotemia, with or without oliguria (< 500 mLlday).

The conditions that often precipitate acute renal failure include hypotension associated with marked volume depletion, heart failure, major surgery, sepsis, angiographic procedures (because the radiocontrast agents are nephrotoxic), and the injudicious use of nephrotoxic antibiotics. These conditions are more common in the elderly, especially those who have many impairments, who are often at increased risk because of preexisting moderate renal insufficiency.
Although acute tubular necrosis (2 to I0 days of oliguria followed by a diuretic phase before function is recovered) is typical in the elderly. nonoliguric acute renal failure is being diagnosed more often. In either case, renal function, as reflected by BUN and serum creatinine levels, is impaired for several days after a brief hypotensive episode. After this brief period of azotemia, renal function gradually returns to its previous level.
Despite the transient loss of renal function, oliguria is not a prominent part of the clinical picture. Since the clinical hallmark of renal failure is generally thought to be a dramatic reduction in urine output, nonoliguric acute renal failure may go unrecognized. Therefore, drugs excreted predominantly via renal mechanisms may inadvertently accumulate during the period of impaired renal function.
The same general principles used in younger patients guide the management of elderly patients with full-blown acute renal failure complicated by oliguria. Most important is the rapid exclusion of urinary obstruction as a cause of I he renal failure, particularly in men with prostatic hypertrophy or carcinoma and in women with gynecologic malignancy.
Treatment
The management of acute renal failure is complex and demanding. The aging kidney retains the capacity to recover from acute ischemic or toxic insults over the course of several weeks.
Dialysis: Dialysis often simplifies management considerably. Hemodialysis, peritoneal dialysis, and the recently introduced forms of hemo-filtration are effective, and the complication rate seems to result more from concurrent cardiovascular disease than from age. It is usually more prudent to initiate dialysis early in a patient with acute renal failure than to wait for an emergency. The indications for emergency dialysis or ultrafiltration therapy include pulmonary edema unresponsive to diuretics, hyperkalemia, uremic pericarditis, seizures, and uncontrolled bleeding due lo uremia.
Femoral vein catheterization for dialysis is a maior advance. These catheters are easily placed, may be left in situ for several days to a week with a very low incidence of infection or thrombosis, and circumvent the need for implantation of arteriovenous shunts.