What is a common mechanism leading to pedal edema?

Pedal edema, which refers to swelling in the feet and ankles, often occurs due to the accumulation of fluid in the interstitial spaces of the tissues. One common mechanism leading to this condition is lymph obstruction. The lymphatic system is responsible for draining excess fluid from the tissues back into the circulatory system. When there is an obstruction in the lymphatic vessels, either due to conditions such as lymphedema, tumors, or infections, fluid cannot be properly drained, resulting in swelling in the affected areas, including the feet.

Increased oncotic pressure typically draws fluid back into the vessels, helping to prevent edema, while decreased capillary permeability would also counteract fluid escaping from the capillaries into the tissues. Increased blood viscosity is not a direct mechanism that leads to pedal edema; rather, it may affect circulation but does not typically cause fluid accumulation in the tissues. Thus, lymph obstruction is the most relevant mechanism for leading to pedal edema as it directly disrupts normal fluid return from the interstitial spaces.