A 68-year-old postoperative hip replacement patient is at risk for deep vein thrombosis (DVT). Which intervention is most effective in preventing pulmonary embolism?

Early ambulation is the most effective intervention for preventing pulmonary embolism (PE) in a postoperative hip replacement patient. Prolonged immobility leads to venous stasis in the lower extremities, which is one of the three components of Virchow's triad — along with hypercoagulability and endothelial injury — that predispose patients to DVT and subsequent PE. Getting the patient moving as soon as safely possible after surgery promotes venous return, reduces stasis, and decreases clot formation risk. This is a well-established, evidence-based standard of care in orthopedic postoperative management. Fluid restriction would worsen hypercoagulability by increasing blood viscosity, making DVT more likely. A heating pad to the calves may provide comfort but does not meaningfully reduce DVT risk and could actually mask symptoms of an existing clot or cause superficial burns in a patient with compromised sensation. Strict bed rest is precisely the condition that creates venous stasis and significantly increases the risk of DVT and PE; it is the opposite of the recommended intervention. While pharmacological prophylaxis such as low-molecular-weight heparin is also critical, among the options listed, early ambulation is the single best answer because it directly addresses venous stasis through physiological means.