edema(redirected from Diabetic macular edema)
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the excessive accumulation of fluid in the organs and intercellular tissue spaces of the body.
Edemas are classified according to the various conditions that can impair the drainage and retention of fluids. High pressure in the capillaries is the major factor in hydremic edemas. Hypoproteinemic edemas are primarily caused by a decrease in the amount of proteins, especially albumins, in the blood and by a drop in the colloidal osmotic, or oncotic, pressure of plasma, which is accompanied by a release of fluid from the capillary bed into the tissues. Membrane-related edemas result from increased capillary permeability owing to the effect of toxic and inflammatory processes and of disturbances of neural regulation in the capillary blood vessels.
Edema can be local—limited to a certain part of the body or organ—or general. Pronounced general edema is determined by inspection and palpation, after which a concavity remains in the edematous area. The condition is usually preceded by a substantial accumulation of fluid (about 4–9 liters) in the body. In persons suffering from heart disease (the commonest cause of hydremic edemas), edema is the most important symptom of cardiac insufficiency. It first arises in the feet and legs when the patient is standing and in the sacrum and lumbar region when the patient is lying down. These conditions then develop into total edema, or anasarca, of the subcutaneous tissue. Several conditions can arise if the fluid accumulates in the natural cavities of the body: hydrothorax is an accumulation in the pleural cavity; ascites, in the abdominal cavity; and hydropericardium, in the pericardial cavity.
Edema—chiefly hypoproteinemic—in the late stages of cirrhosis of the liver is usually combined with ascites and found mainly in the legs, lumbar region, and anterior abdominal wall. In kidney diseases, including nephritis, edema appears all over the body and face, where it is especially pronounced around the eyes. The edematous areas are soft to the touch and covered by pale skin. Salt and water retention in the kidneys, decreased concentration of proteins in the blood, and increased permeability of the vascular walls are major factors in the mechanism of the formation of these types of edema.
Aldosterone promotes fluid retention by causing the retention of sodium ions in the tissues. Thus, endocrine changes that result in the increased production of aldosterone play an important role in the origin of edema in diseases of the heart, kidneys, and liver. The production of the antidiuretic hormone vasopressin also increases in these diseases, resulting in increased reabsorption of water and salts in the renal tubules. Hormonal disturbances are the decisive factor in the development of edema in some endocrine disorders, for example, in Itsenko-Cushing syndrome. The edema observed after prolonged starvation is mainly hypoproteinemic.
Local edema in thrombophlebitis is caused by interference with the outflow of venous blood below the site of the thrombus. In such cases, the edema is firm, purple, painful to the touch, and covered with inflamed skin. When the outflow of lymph through the lymphatic system is disrupted, the surface edema on the limbs is firm, and the skin pale. Inflammatory edemas in such conditions as burns, furuncles, and erysipelas are due to increased capillary permeability and increased flow of blood into the inflamed area. The skin is reddish and painful to the touch.
Treatment of edemas is directed at the causative disease. Diuretics and special diets are prescribed.
REFERENCEEliseev, O. M. Oteki v klinike vnutrennikh boleznei. Moscow, 1970. (Bibliography.)
B. L. ELKONIN