Porth's Essentials of Pathophysiology, 4e

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Integrative Body Functions

U N I T 2

capillary permeability are burn injury, inflammation, and immune responses.

Obstruction of Lymphatic Flow. Osmotically active plasma proteins and other large particles that cannot be reabsorbed through the pores in the capillary membrane rely on the lymphatic system for movement back into the circulatory system. Edema due to impaired lymph flow is commonly referred to as lymphedema . Malignant involvement of lymph structures and removal of lymph nodes during cancer surgery are common causes of lymphedema. Another cause of lymphedema is infection and trauma involving the lymphatic channels and lymph nodes. Manifestations. The effects of edema are determined largely by its location. Edema of the brain, larynx, and lungs are acute, life-threatening conditions. Non–life- threatening edema may interfere with movement, limit- ing joint motion. Swelling of the ankles and feet often is insidious in onset and may or may not be associated with disease. At the tissue level, edema increases the distance for diffusion of oxygen, nutrients, and wastes. Thus, edematous tissues usually are more susceptible to injury and development of ischemic tissue damage, including pressure ulcers. Edema can also compress blood vessels. For example, the skin of a severely swol- len finger can act as a tourniquet, shutting off the blood flow. Edema can also be disfiguring, causing psycho- logical effects and disturbances in self-concept, as well as making it difficult to obtain proper-fitting clothing and shoes. Pitting edema occurs when the accumulation of inter- stitial fluid exceeds the absorptive capacity of the tis- sue gel. In this form of edema, the tissue water becomes mobile and can be translocated with pressure exerted by a finger. Nonpitting edema in which the swollen area becomes firm and discolored, occurs when plasma pro- teins have accumulated in the tissue spaces and coag- ulated. It is most commonly seen in areas of localized infection or trauma. Assessment and Treatment. Methods for assessing edema include daily weight (1 L of water weighs 2.2 pounds), visual assessment, measurement of the affected part, and application of finger pressure to assess for pit- ting edema. Daily weight measurements taken at the same time each day with the same amount of cloth- ing provide a useful index of water gain due to edema. Visual inspection and measurement of the circumference of an extremity can also be used to assess the degree of swelling. This is particularly useful when swelling is due to thrombophlebitis. Finger pressure can be used to assess the degree of pitting edema. If an indentation remains after the finger has been removed, pitting edema is identified. It is evaluated on a scale of +1 (minimal) to +4 (severe) (Fig. 8-5). Distinguishing lymphedema from other forms of edema can be challenging, especially early in its course. Papillomatosis, a characteristic honeycomb appearance

FIGURE 8-5. 3+ pitting edema of the left foot. (Used with permission from Bates B. Bates’ Guide to Physical Examination and HistoryTaking. 6th ed. Philadelphia, PA: J.B. Lippincott; 1995:438.)

of the skin due to dilated lymph vessels that are envel- oped in fibrotic tissue, distinguishes lymphedema from other forms of edema. Computed tomography (CT) or magnetic resonance imaging (MRI) may be used to con- firm the diagnosis. 6 Treatment of edema usually is directed toward main- taining life when the swelling involves vital structures, correcting or controlling the cause, and preventing tissue injury. Edema of the lower extremities may respond to simple measures such as elevating the feet. Diuretic ther- apy commonly is used to treat edema associated with an increase in ECF volume. Serum albumin levels can be measured, and albumin administered intravenously to raise the plasma colloidal osmotic pressure when edema is caused by hypoalbuminemia. Elastic support stockings and sleeves increase intersti- tial fluid pressure and resistance to outward movement of fluid from the capillary into the tissue spaces. These support devices typically are prescribed for patients with conditions such as venous or lymphatic obstruc- tion and are most efficient if applied before the tissue spaces have filled with fluid—for example, in the morn- ing before the effects of gravity have caused fluid to move into the ankles. Moderate to severe lymphedema is usually treated with light-pressure massage designed to increase lymph flow by encouraging opening and closing of lymph vessel valves; compression garments or pneumatic compression pumps; range-of-motion exer- cises; and scrupulous skin care to prevent infection. 6 Third-Space Accumulation Third spacing represents the loss or movement and trap- ping of ECF in a transcompartmental space. The serous cavities are part of the transcompartmental compart- ment (i.e., third space) located in strategic body areas where there is continual movement of body structures— the pericardial sac, the peritoneal cavity, and the pleural cavity. The serous cavities, which are closely linked with