Edema represents fluid leakage from the blood and lymphatic vessels into the soft tissues. Increased total body water, reduced flow through the vessels, changes in blood chemistry, inflammation and positional factors may contribute to fluid leakage into the tissues. The feet and ankles prove particularly susceptible to edema because gravity promotes fluid pooling in these areas of the body.
Prolonged Sitting or Standing
Muscle activity in the legs helps propel blood and lymphatic fluid upward and out of the legs. Prolonged standing or sitting may cause a buildup of fluid within the lower legs due to gravity and diminished propulsive action of the leg muscles. Extended sitting during air, train or automobile travel may cause significant bilateral ankle edema. Similarly, people required to stand in a largely stationary position during their workday may experience repeated episodes of ankle edema. Positional edema often resolves after a night of sleep. Lying down enhances reabsorption of fluid from the tissues back into the circulation.
The total volume of fluid in the circulation increases by approximately 50 percent during pregnancy. The increased fluid causes mild edema throughout the body. Gravitational forces augment this natural pregnancy adaptation, often causing noticeable swelling in the feet and ankles. Lower extremity edema is particularly pronounced late in pregnancy when the enlarged womb compresses the venous and lymphatic vessels in the pelvis and abdomen. While bilateral ankle edema proves common during pregnancy, the sudden onset of marked edema may signal the onset of pre-eclampsia, a dangerous complication of pregnancy.
Obesity commonly causes marked bilateral foot and ankle edema. In a 2006 article published in "Circulation", Dr. Paul Poirier and colleagues report that lymphatic fluid overload, inactivity and heart-related changes associated with obesity contribute to the accumulation of fluid in the soft tissues of the lower extremities.
Heart failure commonly causes bilateral foot and ankle swelling. In a 2005 article published in "American Family Physician", Dr. James O’Brien and colleagues explain that the heart’s decreased pumping capacity seen with heart failure often causes increased water retention by the kidneys. The increased total body water precipitates edema. Treatment with diuretic medications can control this symptom in many heart failure patients.
Acute and chronic kidney failure may cause lower extremity swelling. Loss of protein through the damaged kidneys and total body water overload trigger fluid leakage into the soft tissues. Although gravitational forces typically cause the most marked swelling in the lower extremities, kidney failure can cause edema throughout the body.