Edema is defined as a palpable swelling produced by expansion of the interstitial fluid volume. A variety of clinical conditions are associated with the development of edema, including heart failure, cirrhosis, and the nephrotic syndrome (table 1).
Some patients have localized edema. This can be caused by a variety of conditions, including venous obstruction, as occurs with deep vein thrombosis or venous stasis, and allergic reactions (such as laryngeal edema).
This topic will review the pathophysiology and etiology of generalized edematous states. The clinical manifestations, diagnosis, and therapy of edema are discussed separately. (See "Clinical manifestations and diagnosis of edema in adults" and "General principles of the treatment of edema in adults" and "Treatment of refractory edema in adults".)
PATHOPHYSIOLOGY OF EDEMA FORMATION
There are two basic steps involved in edema formation:
- An alteration in capillary hemodynamics that favors the movement of fluid from the vascular space into the interstitium.
- The retention of dietary or intravenously administered sodium and water by the kidneys.