Pulmonary Embolism
A life-threatening blood clot in the lungs that blocks blood flow, causing sudden shortness of breath and chest pain.
Emergency Management: Cardiac arrest due to PE (often presenting as Pulseless Electrical Activity - PEA). Requires immediate CPR and administration of IV tPA push (Alteplase 50mg IV bolus) during resuscitation efforts, often extending CPR for >20 minutes to allow the drug to work.
A pulmonary embolism is the sudden obstruction of a pulmonary artery or one of its branches, typically by a thrombus that has traveled from the deep veins of the lower extremities. It affects the pulmonary vasculature, causing V/Q mismatch, increased dead space, and right ventricular strain.
Detailed Overview
PE is a life-threatening manifestation of venous thromboembolism (VTE). The clot blocks blood flow to a segment of the lung, preventing gas exchange and severely increasing pulmonary vascular resistance. If the clot burden is large enough, the rapid increase in right ventricular afterload causes acute right heart failure, decreased left ventricular filling, cardiogenic shock, and sudden death. It is a leading cause of preventable hospital mortality.
Epidemiology & Demographics
Incidence is roughly 60-70 per 100,000 population annually. Risk increases exponentially with age, particularly after 60 years. Slight male predominance in older age, but female predominance in childbearing years (due to pregnancy and oral contraceptives).
Etiological Mechanism
The majority (>90%) of pulmonary emboli originate as Deep Vein Thromboses (DVT) in the popliteal, femoral, or iliac veins. Emboli can also consist of fat (post long-bone fracture), air (central line placement), or amniotic fluid, though these are rare.
Primary Causes
Provoked PE is caused by transient risk factors: surgery, trauma, immobility, pregnancy, or estrogen use. Unprovoked PE occurs in the absence of transient risks and is often linked to active malignancy or undiagnosed inherited thrombophilias.
Pathogenesis follows Virchow's Triad: endothelial injury, venous stasis, and hypercoagulability. A thrombus forms in a deep vein, fragments, and embolizes through the right heart into the pulmonary arterial tree. Obstruction of the artery causes a ventilation-perfusion (V/Q) mismatch (ventilated alveoli are not perfused - alveolar dead space), leading to hypoxemia. The body releases serotonin and thromboxane A2 from platelets, causing further pulmonary vasoconstriction. The sudden rise in pulmonary vascular resistance forces the right ventricle to generate higher pressures. A massive PE causes acute RV dilation and failure; the interventricular septum bows into the left ventricle, reducing left ventricular end-diastolic volume, dropping cardiac output, and causing obstructive shock.
Diagnostic Criteria & Guidelines
Clinical probability assessed via Wells Score or Geneva Score. Low probability: normal D-dimer rules out PE. High probability or positive D-dimer: CT Pulmonary Angiography (CTPA) is the gold standard diagnostic test, demonstrating a filling defect in the pulmonary arteries.
For hemodynamically stable PE: Immediate anticoagulation. Direct Oral Anticoagulants (DOACs) are preferred: Apixaban 10 mg PO BID for 7 days, then 5 mg PO BID; OR Rivaroxaban 15 mg PO BID for 21 days, then 20 mg PO daily. Alternatively, Low Molecular Weight Heparin (Enoxaparin 1 mg/kg SC BID) overlapping with Warfarin.
Second-Line & Adjunctive Therapy
For Massive PE (hemodynamically unstable): Systemic thrombolysis with Alteplase (tPA) 100 mg IV over 2 hours. If thrombolysis is contraindicated (e.g., recent surgery, bleeding risk), catheter-directed thrombectomy or surgical pulmonary embolectomy is indicated.
Surgical & Procedural Management
Inferior Vena Cava (IVC) Filter placement if anticoagulation is strictly contraindicated (e.g., active GI bleed) or if recurrent PE occurs despite therapeutic anticoagulation.
Patient Counseling & Advice
Educate on the signs of bleeding while on anticoagulation (melena, hematuria, severe headaches). Advise avoiding contact sports. Counsel women of childbearing age to stop estrogen-containing oral contraceptives immediately.
Follow-Up & Monitoring Schedule
Outpatient follow-up within 2-4 weeks to assess bleeding compliance. Minimum anticoagulation duration is 3 months for provoked PE; lifetime therapy may be needed for unprovoked PE or recurrent VTE. Follow-up echocardiogram at 3-6 months to screen for CTEPH.
Preventive Strategies
VTE prophylaxis in hospitalized patients using Enoxaparin 40 mg SC daily or Heparin 5000 U SC TID. Mechanical prophylaxis (SCDs) if bleeding risk is high.
Untreated PE has a mortality rate up to 30%. With timely anticoagulation, mortality drops to 2-8%. Massive PE presenting with shock carries a 30-50% short-term mortality.