Pulmonary Embolism and Hemodynamics

Pulmonary Embolism

• Pulmonary embolism (PE) occurs when part or all of the pulmonary vascular tree is obstructed, typically due to a thrombus from a distant site.
• The deep venous system of the lower limbs and pelvis accounts for 75% of PE cases.
• Leg thrombi are more likely to embolize from above-the-knee clots (20% incidence) compared to below-the-knee clots.
• Paradoxical emboli can cause strokes in young individuals.
• Septic emboli may arise in endocarditis, especially with intraventricular septal defects or AV shunts.

Hemodynamic Effects

• The impact of PE on hemodynamics is influenced by:
  • The size of the clot,
  • The specific area of the pulmonary vascular tree obstructed,
  • The pre-existing condition of the myocardium.
• Large clots often lodge at the bifurcation of main pulmonary arteries, causing hemodynamic compromise.
• Small clots may travel distally, leading to infarction in regions where blood flow is greatest (commonly lower lobes).
• Mean pulmonary arterial pressure (PAP) does not increase until at least 50% of the vascular bed is occluded.
• Right ventricle (RV) failure may occur when PAP exceeds 40 mmHg, particularly in patients with pre-existing cardiopulmonary disease.
• Associated cardiovascular effects include V/Q mismatch and bronchospasm.
• Respiratory effects may consist of alveolar collapse, pulmonary edema, and systemic hypoxemia.

Resolution and Etiology

• Peripheral pulmonary infarction is more common than central.
• Resolution of PE can take days to weeks through fibrinolysis, requiring the absence of recurrence.
• The etiology of PE involves the activation of the clotting cascade due to:
  • Venous stasis,
  • Injury to the vessel wall,
  • Increased blood coagulability, leading to thrombus formation.
• Venous stasis can be exacerbated by immobility and dehydration, with alterations in coagulation factors seen in acute phase responses, malignancies, and autoimmune diseases.

Risk Factors for Venous Thromboembolism

• Major risk factors include:
  • Extensive abdominal or pelvic surgeries,
  • Orthopedic surgeries, particularly those involving the lower limbs,
  • Post-operative intensive care unit stays,
  • Pregnancy, especially with multiple births and cesarean sections, and conditions like pre-eclampsia.

Explore the critical aspects of pulmonary embolism (PE) and its hemodynamic effects. This quiz covers the causes, impact on the cardiovascular system, and the implications of different clot sizes. Deepen your understanding of how PE can lead to serious complications like strokes and pulmonary infarction.