Pulmonary Embolism I: Introduction

A pulmonary embolism occurs when a thrombus, fat, air, amniotic fluid, or tumor tissue travels through the venous system and blocks pulmonary arteries. It commonly arises from dislodged deep vein thrombosis, hypercoagulable states like inherited thrombophilias, and venous stasis in obesity. Risk factors include prolonged immobility, recent surgery, cancer, oral contraceptives, and pregnancy.

When a thrombus dislodges, it travels through the venous system, passing through the right atrium and ventricle before lodging in the pulmonary arteries. Small emboli may block terminal pulmonary arterioles, causing multiple small lung infarctions. Larger thrombi obstruct major pulmonary arteries, disrupting blood flow and causing ventilation-perfusion mismatch.

Pulmonary artery obstruction increases vascular resistance and elevates pressures in the pulmonary arteries and right ventricle, potentially causing right ventricular failure. The blockage triggers an inflammatory response, causing local vasoconstriction and increased vascular permeability. This creates a ventilation-perfusion mismatch where lung areas receive ventilation but lack perfusion, impairing gas exchange and leading to hypoxemia.

Small emboli may cause vague and transient symptoms including dyspnea, mild to moderate hypoxemia, tachypnea, cough, chest pain, hemoptysis, wheezing or crackles, fever, tachycardia, accentuation of the pulmonic heart sound, and syncope. Symptoms begin gradually or appear suddenly depending on the degree of pulmonary arterial blockage.

Massive pulmonary emboli may result in sudden changes in mental status, feelings of impending doom, hypotension, and cardiorespiratory arrest. These severe manifestations reflect the degree of pulmonary arterial blockage and the severity of hemodynamic and respiratory compromise. Prompt recognition and intervention are critical to manage massive PE and mitigate the risk of fatal outcomes.

Risk factors for pulmonary embolism include prolonged immobility, recent pelvic or lower extremity surgery, history of venous thromboembolism, cancer, obesity, oral contraceptives or hormone therapy, smoking, prolonged air travel over four hours, heart failure, and pregnancy. Endothelial injury from surgery and trauma also increases PE risk.

Obesity promotes pulmonary embolism through venous stasis, a condition where blood flow slows in the veins, increasing the risk of thrombus formation. Venous stasis combined with hypercoagulable states and endothelial injury creates an environment favoring clot development and dislodgement. This mechanism makes obesity a significant etiological factor in PE pathogenesis.