A 55-year-old woman following major abdominal surgery has had discomfort and swelling of her left leg for the past week. On physical examination, the leg is slightly difficult to move, and on palpation there is tenderness. A Doppler sonogram shows thrombosis of deep left leg veins. Which of the following mechanisms is most likely to contribute to her condition?

The most important and the most common cause of venous thrombosis is vascular stasis, which often occurs with immobilization. Calcium is a cofactor in the coagulation pathway, but an increase in calcium has minimal effect on the coagulation process. Aspirin inhibits platelet function and limits thrombosis. Nitric oxide is a vasodilator and an inhibitor of platelet aggregation. Turbulent blood flow may promote thrombosis, but this risk factor is more common in fast-flowing arterial circulation.