Pulmonary Embolism I: Introduction

A blood clot, or thrombus, is a semi-solid mass composed of fibrin, platelets, and red blood cells. When it forms within a vessel, it can obstruct blood flow, known as thrombosis. If part of the clot detaches, it becomes an embolus that can travel and block distant vessels. When this occurs in the pulmonary arteries, it causes a condition known as pulmonary embolism (PE).

Origin and Impact

Most often, the embolus originates from a thrombus in the deep veins of the lower limbs, a condition called deep vein thrombosis, or DVT. Together, DVT and PE are considered part of the same disease process: venous thromboembolism, or VTE. While small emboli may be filtered by the lungs, larger or multiple clots can obstruct circulation, impair gas exchange, increase pulmonary pressure, and strain the right heart, potentially leading to failure or sudden death.

Virchow’s Triad

Pulmonary embolism development is explained by three key factors.

• Venous stasis occurs when blood flow slows or becomes stagnant with immobility in conditions such as surgery, heart failure, obesity, pregnancy, or catheter use.
• Hypercoagulability may be inherited (e.g., factor V Leiden, protein C/S deficiency) or acquired (e.g., malignancy, oral contraceptives, pregnancy, inflammatory disorders).
• Endothelial injury or damage to the inner lining of blood vessels from trauma, surgery, or prior thrombosis activates clotting pathways.

High-Risk Groups

Hospitalized and cancer patients are at increased risk due to immobility, inflammation, and procoagulant states. Understanding these mechanisms supports early detection, prevention, and management of pulmonary embolism.