Amanda is an 18-year-old with anorexia nervosa. She was recently admitted to an eating disorders ...

Amanda was presenting with low serum albumin. Albumin has a low molecular weight and high concentration in the plasma, allowing it to create a strong colloidal osmotic pressure. When albumin levels are decreased, the serum osmotic gradient declines. Fluid therefore leaves the capillaries to the surrounding interstitial space.

Pitting edema is a result of an increased level of interstitial fluid that exceeds the absorptive capacity of the tissue gel. The edema is mobile and can shift with pressure. Nonpitting edema involves the migration of capillary fluid and plasma proteins into the tissue space. The protein coagulates and creates a firm edema that does not move with pressure.

Edema increases the distance between tissue cells and circulation. The diffusion of gases, nutrients, and wastes between tissue cells and capillaries is consequently decreased. Edema can also mechanically compress tissue capillaries. Both situations leave tissues prone to ischemic damage and, when the patient is immobile, pressure ulcers.