edema

What is edema?

Edema is observable swelling from fluid accumulation in body tissues. Edema most commonly occurs in the feet and legs, where it is referred to as peripheral edema. The swelling is the result of the accumulation of excess fluid under the skin in the spaces within the tissues. All tissues of the body are made up of cells and connective tissues that hold the cells together. This connective tissue around the cells and blood vessels is known as the interstitium. Most of the body's fluids that are found outside of the cells are normally stored in two spaces; the blood vessels (as the "liquid" or serum portion of your blood) and the interstitial spaces (not within the cells). In various diseases, excess fluid can accumulate in either one or both of these compartments.

The body's organs have interstitial spaces where fluid can accumulate. An accumulation of fluid in the interstitial air spaces (alveoli) in the lungs occurs in a disorder calledpulmonary edema. In addition, excess fluid sometimes collects in what is called the third space, which includes cavities in the abdomen (abdominal or peritoneal cavity - called "ascites") or in the chest (lung or pleural cavity - called "pleural effusion"). Anasarca refers to the severe, widespread accumulation of fluid in the all of the tissues and cavities of the body at the same time.

What is pitting edema and how does it differ from non-pitting edema?

Pitting edema can be demonstrated by applying pressure to the swollen area by depressing the skin with a finger. If the pressing causes an indentation that persists for some time after the release of the pressure, the edema is referred to as pitting edema. Any form of pressure, such as from the elastic in socks, can induce pitting with this type of edema.

In non-pitting edema, which usually affects the legs or arms, pressure that is applied to the skin does not result in a persistent indentation. Non-pitting edema can occur in certain disorders of the lymphatic system such aslymphedema, which is a disturbance of the lymphatic circulation that may occur after a mastectomy, lymph node surgery, or congenitally. Another cause of non-pitting edema of the legs is called pretibial myxedema, which is a swelling over the shin that occurs in some patients with hyperthyroidism. Non-pitting edema of the legs is difficult to treat. Diuretic medications are generally not effective, although elevation of the legs periodically during the day and compressive devices may reduce the swelling.

The focus of the rest of this article is on pitting edema, as it is by far the most common form of edema.

What causes pitting edema?

Edema is caused by either systemic diseases, that is, diseases that affect the various organ systems of the body, or by local conditions involving just the affected extremities. The most common systemic diseases associated with edema involve the heart, liver, and kidneys. In these diseases, edema occurs primarily because of the body's retention of too much salt (sodium chloride). The excess salt causes the body to retain water. This water then leaks into the interstitial tissue spaces, where it appears as edema.

The most common local conditions that cause edema are varicose veins andthrombophlebitis (inflammation of the veins) of the deep veins of the legs. These conditions can cause inadequate pumping of the blood by the veins (venous insufficiency). The resulting increased back-pressure in the veins forces fluid stay in the extremities (especially the ankles and feet). The excess fluid then leaks into the interstitial tissue spaces, causing edema.

Why does edema occur in patients with kidney disease?

Edema forms in patients with kidney disease for two reasons:

1. a heavy loss of protein in the urine, or
2. 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:

• enalapril (Vasotec),
• quinapril (Accupril),
• captopril (Capoten),
• benazepril (Lotensin),
• trandolapril (Mavik),
• lisinopril (Zestril or Prinivil), and
• ramipril (Altace).

Angiotensin receptor blockers include:

• losartan (Cozaar),
• valsartan (Diovan),
• candesartan (Atacand), and
• irbesartan (Avapro).

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.

treat edema

Edema can become a problem in systemic diseases of the heart, liver or kidneys. Diuretic therapy can be initiated, often alleviating the edema. The most potent diuretics are loop diuretics, so-called because they work in the portion of the kidney tubules referred to as the loop of Henle. The kidney tubules are small ducts that regulate salt and water balance, while transporting the forming urine. Clinical loop diuretics available are:

• furosemide (Lasix),
• torsemide (Demadex), and
• butethamine (Bumex).

The doses of these diuretics vary depending upon the clinical circumstances. These drugs can be given orally, although seriously ill patients in the hospital may receive them intravenously for more prompt or effective response. If one of the loop diuretics is not effective alone, it may be combined with an agent that works further down (more distally) in the tubule. These agents include the thiazide type diuretics, such as hydrochlorothiazide (HydroDIURIL), or a similar but more potent type of diuretic called metolazone (Zaroxolyn). When diuretics that work at different sites in the kidney are used together, the response often is greater than the combined responses to the individual diuretics (synergistic response).

Some diuretics frequently cause an excessive loss of potassium in the urine, leading to the depletion of body potassium. These drugs include the loop diuretics, the thiazide diuretics, and metolazone. Patients on these diuretics are commonly advised to take potassium supplements and/or to eat foods high in potassium. High potassium foods include certain fruits such as:

• bananas,
• orange juice,
• tomatoes, and
• potatoes.

Patients with impaired kidney function often do not require potassium supplements with diuretics because their damaged kidneys tend to retain potassium. In certain instances, the volume of urine induced by the diuretic can be improved by adding a potassium-sparing diuretic, one that does not cause depletion of potassium. These diuretics include spironolactone(Aldactone), triamterene (Dyrenium, a component of Dyazide), and amiloride(Midamor). Adding one of these diuretics to the patient's diuretic regimen may preclude the need for potassium supplements. Another diuretic that can be used is acetazolamide (Diamox), which counteracts the development of an increased concentration of bicarbonate (too much alkali) in the blood. Increased bicarbonate sometimes occurs in patients receiving other diuretics.