Pulmonary Embolism
A venous clot, usually from a deep leg or pelvic vein, lodges in the pulmonary arterial tree, obstructing perfusion and abruptly loading the right ventricle.
Definition
Pulmonary embolism is obstruction of the pulmonary arterial circulation by thrombus, usually embolised from a deep vein. It forms part of venous thromboembolism and ranges from a small peripheral embolus to high-risk PE causing obstructive shock. NICE separates provoked from unprovoked disease by whether a transient major risk factor was present, because that distinction decides treatment duration.
First principles
A venous clot becomes a pulmonary vascular obstruction
Most pulmonary emboli arise from deep venous thrombosis in the leg or pelvis. A fragment breaks off, passes through the right heart and lodges in a pulmonary artery. Stasis, endothelial injury and hypercoagulability explain the risk factors. NICE calls a clot provoked when a transient major risk factor was present within 3 months: surgery, trauma, significant immobility, pregnancy or the puerperium, or hormonal therapy. Without one it is unprovoked, and that single word sets how long treatment runs.
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