Pulmonary Embolism I: Introduction

A blood clot, or thrombus, forms within blood vessels and can block blood flow partially or completely. This condition is known as thrombosis.

If part of the clot breaks away and travels through the bloodstream, it becomes an embolus.

If the embolus lodges in a pulmonary artery, it can lead to a pulmonary embolism, or PE. In most cases, the embolus originates from a thrombus in the deep veins of the legs—a condition called deep vein thrombosis.

The development of PE is explained by Virchow’s triad, which includes venous stasis, hypercoagulability, and endothelial injury, three factors that contribute to thrombus formation.

Venous stasis may result from prolonged immobility, such as after orthopedic surgery or long periods of sitting, like on extended plane flights.

Hypercoagulability may result from conditions like antithrombin III deficiency, pregnancy, or the use of estrogen-containing contraceptives.

Endothelial injury may be caused by trauma or central venous catheterization.