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Alternative namesAzotemia - prerenal; Uremia; Renal underperfusion
DefinitionPrerenal azotemia is an abnormally high level of nitrogen-type wastes in the bloodstream, caused by conditions that reduce blood flow to the kidneys.
Causes, incidence, and risk factors
Prerenal azotemia is not uncommon, especially in hospitalized patients. It is a result of conditions that impair blood flow to the kidney. The kidneys normally filter the blood, forcing it under pressure through the glomeruli (structures in the kidneys).
When the volume or pressure of the blood flow through the kidney decreases, glomerular filtration is reduced drastically, and may not occur at all. Little or no urine is formed, and waste products remain in the bloodstream even though the internal structures of the kidney are intact and functional.
The glomeruli and tubules continue to filter wastes, but the rate of filtration is so slow that many of these wastes are reabsorbed into the blood, rather than being excreted in the urine.
Conditions where the volume is not lost, but where the heart cannot pump enough blood, or the blood is pumped at low volume, also increase risk for prerenal azotemia. These conditions include shock (such as septic shock ), heart failure , and conditions where the blood flow to the kidney is interrupted, such as trauma to the kidney, surgery of various types, renal artery embolism , and other types of renal artery occlusion .
Signs and tests
An examination may show signs of low cardiac output or signs of hypovolemia . The blood pressure may be low or may drop when the person stands up. The pulse pressure (difference between systolic blood pressure and diastolic blood pressure) may be reduced. The heart rate may be rapid.
Skin turgor may be poor, mucous membranes may be dry. The neck veins may be collapsed. There may be little or no urine in the bladder even when drained by a catheter. If the condition is prolonged, other signs of acute renal failure may be present.
TreatmentThe main goal of treatment is to rapidly correct the cause of the prerenal azotemia before damage occurs to the internal kidney structures. Hospitalization is often required, and may involve treatment in an intensive care unit. Treatment may include hemodialysis or peritoneal dialysis.
Intravenous fluids, including blood or blood products, may be used to increase blood volume. After blood volume has been restored, medications may be used to increase blood pressure and cardiac output. These may include dopamine , dobutamine, and similar cardiac medications. The cause of the decreased blood volume or blood pressure should be identified and treated as appropriate.
If other symptoms of acute renal failure are present, treatment for it should continue, including medications, dietary restrictions, or dialysis.
Expectations (prognosis)Prerenal azotemia is reversible if the cause can be identified and corrected within 24 hours. However, if the cause is not corrected quickly, damage may occur to the internal structures of the kidney ( acute tubular necrosis ).
Calling your health care providerGo to the emergency room or call the local emergency number (such as 911), if symptoms indicating prerenal azotemia may be present.
PreventionPrompt treatment of any condition that reduces the volume or force of blood flow through the kidneys may help to prevent prerenal azotemia from developing.
Update Date: 1/19/2004Irfan A. Agha, M.D., Department of Medicine, St. Louis University, St. Louis, MO. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT