Edema involving the right lower extremity may be caused by:

• A. Increased intravenous pressure
• B. Decreased intravenous pressure
• C. Decreased venous hypervolemia
• D. Increased extravascular pressure

Answer: (A)

Edema in a dependent leg typically comes from increased capillary hydrostatic pressure due to higher venous pressure. When venous pressure in the leg rises, the pressure pushing fluid out of capillaries into the surrounding tissue increases. Fluid filters into the interstitial space faster than it can be cleared by lymphatics, leading to accumulation and swelling. Gravity makes the lower extremities especially susceptible, so the right leg can swell when venous pressure is elevated.

If venous pressure were reduced, or venous blood volume were decreased, the force driving fluid into the interstitial space would be diminished, making edema less likely. Increasing the pressure outside the vessels (extravascular pressure) would oppose filtration, not promote it, so it wouldn’t cause edema.