Edema (cont.)
Why does edema occur in patients with kidney disease?
Edema forms in patients with kidney disease for two reasons:
- a heavy loss of protein in the urine, or
- impaired kidney (renal) function.
Heavy loss of protein in the urine
In this situation, the patients have normal or fairly normal kidney function. The heavy loss of protein in the urine (over 3.0 grams per day) with its accompanying edema is termed the
nephrotic syndrome. Nephrotic syndrome results in a reduction in the concentration of albumin in the blood (hypoalbuminemia). Since albumin helps to maintain blood volume in the blood vessels, a reduction of fluid in the blood vessels occurs. The kidneys then register that there is depletion of blood volume and, therefore, attempt to retain salt. Consequently, fluid moves into the interstitial spaces, thereby causing pitting edema.
The treatment of fluid retention in these patients is to reduce the loss of protein into the urine and to restrict salt in the diet. The loss of protein in the urine may be reduced by the use of ACE inhibitors and
angiotensin receptor blockers (ARB's). Both categories of drugs, which ordinarily are used to lower blood pressure, prompt the kidneys to reduce the loss of protein into the urine.
ACE inhibitor drugs include:
Angiotensin receptor blockers include:
Certain kidney diseases may contribute to the loss of protein in the urine and the development of edema. A biopsy of the kidney may be needed to make a diagnosis of the type of kidney disease, so that treatment may be given.
Impaired kidney (renal) function
In this situation, patients who have kidney diseases that impair renal function develop edema because of a limitation in the kidneys' ability to excrete sodium into the urine. Thus, patients with kidney failure from whatever cause will develop edema if their intake of sodium exceeds the ability of their kidneys to excrete the sodium. The more advanced the kidney failure, the greater the problem of salt retention is likely to become. The most severe situation is the patient with end-stage kidney failure who requires dialysis therapy. This patient's salt balance is totally regulated by dialysis, which can remove salt during the treatment. Dialysis is a method of cleansing the body of the impurities that accumulate when the kidneys fail. Dialysis is accomplished by circulating the patient's blood over an artificial membrane (hemodialysis) or by using the patient's own abdominal cavity (peritoneal membrane) as the cleansing surface. Individuals whose kidney function declines to less than 5% to 10% of normal may require dialysis.
Next: What is idiopathic edema? »
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