ACUTE RENAL FAILURE

1 ACUTE RENAL FAILURE

General Discussion

Although there is no universal definition for acute renal failure, accepted diagnostic criteria include an increase in the serum creatinine level of 0.5 mg/dL if the baseline is less than 2.5 mg/dL, an increase in serum creatinine by more than 20% if the baseline is more than 2.5 mg/dL, a 50% decrease in the baseline calculated glomerular filtration rate (GFR), or the need for acute kidney replacement therapy. The GFR decreases over days to weeks in acute renal failure, and patients are often asymptomatic. Complete renal shutdown is present when the serum creatinine level rises by at least 0.5 mg/dL per day and the urine output is less than 400 mL per day.

False elevations of the serum creatinine can be seen with medications such as trimethoprim–sulfamethoxazole, cimetidine, and cephalosporins because these agents can inhibit the tubular secretion of creatinine without causing actual damage to the kidneys. However, these medications can also cause renal failure as a result of interstitial nephritis.

The causes of acute renal failure (ARF) can be broadly divided into three categories. The first is prerenal ARF, which is a reversible increase in serum creatinine and blood urea nitrogen (BUN) that results from decreased renal perfusion, leading to a reduction in the GFR. The second category is postrenal ARF, which is caused by an obstruction of the urinary collection system by either intrinsic or extrinsic masses. The third category is intrinsic ARF, in which the structures of the nephron are affected. This third category can be further subdivided on the basis of the structure that is affected: the glomeruli, tubules, interstitium, or vasculature.

Prerenal acute renal failure accounts for 60–70% of cases of acute renal failure. The major cause of intrinsic ARF is acute tubular necrosis (ATN), which is caused by an ischemic or nephrotoxic injury to the kidney.

It is always important to exclude a possible obstructive cause in a patient presenting with acute renal failure since prompt intervention may result in improvement or complete recovery of renal function. Bladder catheterization may be considered, especially in elderly men with unexplained ARF. Renal ultrasonography can be used to diagnose obstruction by assessing for hydronephrosis.

Probable causes of ARF may be identified from the history and physical examination. Urine collected before the initiation of intravenous fluid or diuretic treatment can be used to calculate the fractional excretion of sodium (FENa) using the following equation:

A FENa less than 1% suggests a prerenal cause of ARF. A FENa greater than 1% suggests an intrinsic cause of ARF, most commonly ATN. The FENa is often greater than 3% in intrinsic causes of ARF. It should be noted that a prerenal FENa of greater than 1% can occur in patients receiving chronic diuretic therapy or in patients with ARF superimposed on chronic renal failure. Conversely, an intrinsic FENa of less than 1% can occur with radiocontrast nephropathy and rhabdomyolysis.

Causes of Acute Renal Failure

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Aug 17, 2016 | Posted by admin in PEDIATRICS | Comments Off

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