Topic overview

Start with the big picture

Edema is excess interstitial fluid arising from changes in hydrostatic or oncotic pressure, sodium and water retention, lymphatic obstruction, or increased vascular permeability. Its distribution may be localized or generalized, and the fluid may be a low-protein transudate or an inflammation-associated, protein-rich exudate. Assessment includes features such as pitting and non-pitting swelling. Hyperemia is an active increase in blood flow from arteriolar dilation, whereas congestion is passive accumulation caused by impaired venous outflow. Persistent congestion can produce characteristic tissue changes, including pulmonary hemosiderin-laden cells and fibrosis, a nutmeg appearance of the liver, or congestive splenomegaly. The lesson connects these mechanisms with their clinical consequences and organ-specific patterns.