Pulmonary embolism: Meaning (information, definition, explanation, facts)

A pulmonary embolism occurs when a blood clot, generally a venous thrombus, becomes dislodged from its site of formation and embolizes to the arterial blood supply of one of the lungs, causing vascular obstruction and impaired gas exchange.

Signs and symptoms

Signs of PE are (sudden) shortness of breath (dyspnea), rapid breathing rate (tachypnea), pleuritic chest pain, cough, hemoptysis (coughing up blood), and in severe cases, hypotension, loss of consciousness, and death.

The most common sources of embolism are pelvic vein thromboses or proximal leg deep venous thrombosis (DVTs).

Generally PE's are caused by a synergism of several predisposing factors, roughly to be divided into genetic, acquired and circumstantial causes:

• Genetic
  • Factor V, Leiden type (3% of the population are heterozygous for FVL (G1691A).
  • Prothrombin mutation (G20210A).
  • Protein C deficiency.
  • Protein S deficiency.
  • Antithrombin III deficiency.
  • High homocysteine levels due to MTHFR mutation.
  • Plasminogen and fibrinolysis disorders.
• Acquired
  • antiphospholipid antibodies
    • anticardiolipin antibodies and/or
    • lupus anticoagulants
  • Renal disease (renal loss of antithrombin)
  • Paroxysmal nocturnal hemoglobinuria
  • Use of the oral contraceptive pill
• 'Circumstantial'
  • Immobilisation, e.g. after-
  • Surgery
  • Trauma
  • Obesity
  • Pregnancy
  • Cancer (Trousseau's syndrome)

The diagnosis of pulmonary embolism (PE), suspected on the basis of shortness of breath and chest pain, with or without an abnormal x-ray, can be confirmed by a medical test called a "ventilation-perfusion scan" (or V/Q scan), which shows that some areas of the lung are being ventilated but not perfused with blood (due to obstruction by a clot).

Recent research has shown that in low suspicion of PE, a blood test (D dimer) might be enough to exclude the possibility of PE as cause of someone's symptoms.

Instead of the V/Q scan spiral computed tomography (spiral CT) is increasingly being used, especially when other lung disorders are part of the differential diagnosis.

When a PE is being suspected, a number of blood tests are also done, in order to exclude important secondary causes of PE. This includes a full blood count, clotting status (PT, APTT, TT), and some screening tests (Erythrocyte sedimentation rate, renal function, liver enzymes, electrolytes). If one of these is abnormal, further investigations might be warranted.

Treatment is via infusion of thrombolytic drugs (only in submassive PE) and anticoagulation (heparin or low-molecular weight heparin, later warfarin or coumadins - generally for 6 months).

Prognosis depends on the amount of lung that is affected and on the co-existence of other debilitating conditions. Chronic embolisation to the lung can lead to pulmonary hypertension.

After a first PE, the search for secondary causes is usually brief. Only when a second PE occurs, and especially when this happens while still under anticoagulant therapy, a further search for underlying conditions is undertaken. This will include testing (see above for full list) for Factor V Leiden mutation, antiphospholipid antibodies, protein C and S and antithrombin levels, and later prothrombin mutation, MTHFR mutation, Factor VIII concentration and rarer inherited coagulation abnormalities.