Topic overview

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Edema can develop through increased capillary hydrostatic pressure, reduced plasma oncotic pressure, increased capillary permeability, lymphatic obstruction, or renal sodium and water retention. These mechanisms are associated with conditions such as heart failure, low plasma protein states, inflammation, venous blockage, and renal dysfunction. Edema may be generalized or localized, dependent or non-dependent, and pitting or non-pitting. Comparing transudates with exudates can also help guide consideration of the underlying process. Special forms include pulmonary edema, which impairs gas exchange, and cerebral edema, classified by its underlying mechanism. Diagnostic evaluation draws on fluid-balance principles and supporting findings such as serum albumin, BNP, and urinary sodium.