Along with anticoagulation, strict bed rest has long been standard therapy for patients with acute deep vein thrombosis (DVT). Activity restriction is based on the assumption that restricting movement reduces the risk that a thrombus will break away from the deep vein and cause pulmonary embolism (PE).

Testing this assumption, Spanish researchers made a surprising discovery: Bed rest had no effect on the risk of developing symptomatic PE among over 2,000 patients with acute DVT or submassive PE.

The 15-day study involved 2,650 patients, 2,038 with DVT and 612 with PE. Fifty-two percent of patients with DVT and 63% of patients with PE were put on strict bed rest.

New, symptomatic PE events were experienced by 0.5% of patients with DVT and 0.7% of patients with PE-11 and 4 patients, respectively. Five of these patients died of PE. But when researchers compared bedridden and ambulatory patients, they found no significant differences in new PE events, fatal PE, or bleeding complications.

The study was based on analysis of data from a registry of consecutively enrolled patients with symptomatic, acute DVT or PE. Initiated in Spain, the registry is currently open to other countries, making it an international registry. The researchers note several study characteristics that could have introduced bias: The registry isn't a prospective, randomized, controlled trial; ambulation may have been prescribed to healthier patients; and not all patients were evaluated for both symptomatic and asymptomatic recurrences.

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