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Why can prolonged surgery or bed rest increase the chance of a venous blood clot?

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Fibrin in blood clotting — bleeding and blood clotting Red blood cells (erythrocytes) trapped in a mesh of fibrin threads. Fibrin, a tough, insoluble protein formed after injury to the blood vessels, is an essential component of blood clots.

Prolonged surgery and bed rest increase the risk of a venous blood clot primarily by causing reduced blood flow, a condition known as stasis.1

Under normal circumstances, the movement of blood through veins relies on the contraction of muscles. During periods of prolonged inactivity—such as recovery from major surgery or being bedridden due to illness—these muscles do not contract sufficiently to facilitate normal circulation. This lack of movement leads to blood pooling in the veins, which significantly increases the likelihood of thrombosis, or the formation of a blood clot.21

Additionally, major surgery can cause direct injury to a vein, which further elevates the risk of developing deep vein thrombosis (DVT). Because DVT can lead to life-threatening complications like pulmonary embolism, medical professionals emphasize the importance of resuming movement as soon as possible following surgery or illness to encourage healthy blood flow.12