11. Pulmonary embolism

Definition

• Entity of peripheral vein thrombosis followed by embolisation of the thrombus into a branch of the pulmonary artery leading to hypertension and necrosis of pulmonary parenchyme!

Etiology

• Most often appears as a result of acute PTE
• Sources of thrombi include:
• Pelvic and abdominal veins
• DVT
• Hypercoagulable states
• Amniotic emboli
• Fat emboli from long bones
• ARDS

Risk factors of PTE

• Acquired- age, immobilization, traumas, estrogens, weight, COPD, HF, sepsis, neoplasms, polychemotherapy, nephrotic syndrome
• Genetic- deficiency of antithrombine, protein C and S, hyperhomocysteinemia, high conc of factors VIII, IX, XI

Pathophysiology

• The deep venous thrombi of legs and pelvis are the most usual origin of pulmonary thromboemboli
• They embolise into the pulmonary arteries and cause hemodynamic and gas exchange disturbances
• Sudden increase of RV afterload can cause RV dilation and hypokinesia, tricuspid regurgitation and then RV failure
• The decreased RV output and septal shift to left in diastole impedes LV filling
• Changes of coronary circulation are due to a reduced transcoronary pressure gradient (which is due to aortic hypotension and increased RA pressure)
• This reduces myocardial blood flow and hypoperfusion of RV endocardium
• Lung perfusion is decreased but perfusion is the same
• Increased dead space and impaired gaseous exchange
• After some hours, the non-perfused lung no longer produces surfactant so alveolar collapse occurs