Pulmonary Thromboembolism

Introduction

• Defined as occlusion of a pulmonary artery from embolization of a thrombus from a distal site
  • size of embolism determines proximity of occlusion to pulmonary trunk
    • Saddle embolus
      • large clot that occludes central pulmonary arteries
  • most commonly due to a thromboembolism from the deep veins of the leg
    • highest number originate from femoral vein
• Risk factors
  • Virchow’s triad
    • stasis
      • immobility
      • CHF
      • obesity
      • surgery
    • hypercoagulability
      • pregnancy
      • OCP 
      • protein C/S deficiency
      • factor V Leiden
      • severe burns
      • cancer
    • endothelial damage
      • exposed collagen stimulates clotting cascade
        • trauma
        • fracture
• previous DVT

Presentation

• Dyspnea and tachycardia common presenting findings
• May see hypoxemia on pulse oximetry and ABG
  • ABG often shows ↓ P_O2, ↓ P_CO2, ↑ A-a gradient  
• Pleuritic chest pain 
• Sudden death
  • acute right heart failure from rapid increase in pulmonary artery pressure
  • more common with saddle embolism
• Pleural friction rub
• Fever
  • if pulmonary infarct
• Deep vein thrombosis
  • Homans’ sign
    • dorsiflexion of foot leads to tender calf muscle
    • not present in the majority of cases (not sensitive or specific)
• erythematous, swollen, warm, lower extremity

Imaging

• Chest CT with angiography
  • test of choice in most circumstances
  • visualize filling defect in pulmonary artery
• V/Q radionuclide scan
  • ↓ pulmonary perfusion without decreased ventilation to given area
  • used when patient cannot tolerate CT contrast (renal failure, pregnancy)
  • requires a normal chest xray to be useful
• pulmonary angiogram
  • gold-standard confirmatory test
• rarely used

Studies

• Labs
  • serum D-dimers 
    • result of clot degradation
    • only useful if low pretest probability (Wells criteria)
• high sensitivity but low specificity

Treatment

• Pharmacologic
  • anticoagulation 
    • heparin or low-molecular weight heparin (LMWH)
    • warfarin
      • begin for long term anticoagulation
  • thrombolysis
    • in cases of hemodynamic compromise
• Operative
  • inferior vena cava filter
    • indicatied if anticoagulation is contraindicated or if patient develops a PE while on  anticoagulants
  • thrombectomy
    • in cases of hemodynamic compromise and contraindication to thrombolytic therapy
• Prevention
  • Subcutaneous heparin or LMWH most effective for immobile patients or patients at high risk 
  • early ambulation as able
• Sequential compression devices when pharmacologic prophylaxis is contraindicated

• Pulmonary infarction
  • most cases do not result in infarction due to large degree of collateral circulation in the lungs
  • occur when patient has a reduction in pulmonary blood flow
    • secondary to decreased cardiac output or obstructive lung disease
• Death
  • Due to right ventricular failure