pulmonary embolism (PE) is a sudden blockage of one or more branches of the pulmonary arteries, typically caused by a blood clot (thrombus) that has traveled to the lungs from another part of the body, most often from the deep veins of the legs (deep vein thrombosis, or DVT). It is a life-threatening condition that disrupts pulmonary blood flow, impairs oxygenation, and can lead to right ventricular strain or failure.
Pathophysiology
Thrombus Formation: Most commonly originates in the deep veins of the lower extremities.
Embolization: The thrombus dislodges and travels through the venous system to the right heart and pulmonary arteries.
Vascular Obstruction:
Reduces blood flow in the pulmonary circulation.
Increases pulmonary artery pressure and right ventricular workload.
Ventilation-Perfusion (V/Q) Mismatch:
Ventilated areas of the lung are not perfused, leading to hypoxemia.
Causes
Thromboembolic (most common):
Deep vein thrombosis (DVT).
Non-thrombotic (rare):
Fat embolism (e.g., long bone fractures).
Air embolism (e.g., surgery, trauma).
Amniotic fluid embolism (e.g., during labor).
Tumor embolism (e.g., metastatic cancers).
Risk Factors
Venous Stasis:
Prolonged immobility (e.g., bed rest, long flights).
Hypercoagulable States:
Genetic (e.g., Factor V Leiden, prothrombin mutation).
Acquired (e.g., cancer, pregnancy, oral contraceptive use).
Endothelial Injury:
Trauma, surgery, or indwelling catheters.
Clinical Presentation
Symptoms:
Sudden onset of dyspnea (shortness of breath).
Chest pain, often pleuritic.
Cough, sometimes with hemoptysis.
Signs:
Tachypnea (rapid breathing).
Tachycardia.
Hypoxia.
Hypotension (in massive PE).
Signs of DVT (e.g., swollen, painful leg).
Diagnosis
Imaging:
CT Pulmonary Angiography (CTPA):
Gold standard for diagnosis.
Shows filling defects in pulmonary arteries.
Ventilation-Perfusion (V/Q) Scan:
Used in cases where CTPA is contraindicated (e.g., pregnancy, renal impairment).
Ultrasound:
For DVT detection in the lower extremities.
Laboratory Tests:
D-dimer:
Elevated in PE but non-specific; useful for ruling out PE in low-risk patients.
Arterial Blood Gas (ABG):
Hypoxemia and respiratory alkalosis.
ECG:
May show signs of right heart strain (e.g., S1Q3T3 pattern, right axis deviation).
Echocardiography:
Evaluates right heart strain in massive PE.
Treatment
Anticoagulation:
First-line therapy to prevent further clot formation.
Heparin (unfractionated or low-molecular-weight) or direct oral anticoagulants (DOACs).
Thrombolysis:
For massive or high-risk PE with hemodynamic instability.
Surgical or Catheter-Based Thrombectomy:
In cases where thrombolysis is contraindicated or ineffective.
Supportive Care:
Oxygen therapy for hypoxia.
Hemodynamic support (e.g., fluids, vasopressors).
Complications
Chronic thromboembolic pulmonary hypertension (CTEPH).
Right heart failure.
Sudden death (in untreated or massive PE).