It is the purpose of this paper to outline the clinical syndromes in which edema significantly appears, to discuss their differentiation, and to comment on the changes to which edema itself may give rise. The frequency with which edema occurs indicates the variety of its origins. Its physiologic bases have been reviewed in a former paper.1
Conditions in which edema commonly appears are summarized in Table 1. Although clinical edema usually involves more than one physiologic mechanism, it is not difficult to determine the predominant disturbance. Table 2 illustrates the physiologic mechanisms of clinical edema.
Physiologically, edema is an excessive accumulation of interstitial fluid. Clinically, it may be latent or manifest, and, by its nature, localized or generalizing. These terms, with the exception of generalizing, have been defined, and may be accepted. By generalizing edema is meant a condition in which edema is at first local in its appearance, but in which, as the process extends, edema will become general, causing anasarca. The degree of edema in any area is limited by tissue tension and the sites of its first appearance and later spread are partly determined by gravity.
Generalizing edema is an early manifestation of cardiac failure. It is usually considered to be evidence of inadequacy of the right ventricular musculature (back pressure theory). Peripheral edema may be accompanied by pulmonary edema in cases where there is simultaneous left ventricular failure. Actually, the genesis of cardiac edema may depend more on sodium retention2,3,4 due to “forward cardiac. . .