Risk Factors for Pulmonary embolism

Risk Factors for Pulmonary embolism/Pulmonary embolism (PE) is a blockage of an artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream (embolism). Symptoms of a PE may include shortness of breath, chest pain particularly upon breathing in and coughing up blood. Symptoms of a blood clot in the leg may also be present, such as a red, warm, swollen, and painful leg.  Signs of a PE include low blood oxygen levels, rapid breathing, rapid heart rate, and sometimes a mild fever. Severe cases can lead to passing out, abnormally low blood pressure, and sudden death.

Causes of pulmonary embolism

Underlying causes

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 (“thrombophilia screen”) 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.^[rx]

Probability testing

There are additional prediction rules for PE, such as the Geneva rule. More importantly, the use of any rule is associated with a reduction in recurrent thromboembolism.^[rx]

The Wells score:

• clinically suspected DVT — 3.0 points
• alternative diagnosis is less likely than PE — 3.0 points
• tachycardia (heart rate > 100) — 1.5 points
• immobilization (≥ 3d)/surgery in previous four weeks — 1.5 points
• history of DVT or PE — 1.5 points
• hemoptysis — 1.0 points
• malignancy (with treatment within six months) or palliative — 1.0 points

Traditional interpretation

• Score >6.0 — High (probability 59% based on pooled data)
• Score 2.0 to 6.0 — Moderate (probability 29% based on pooled data)
• Score <2.0 — Low (probability 15% based on pooled data)

Alternative interpretation

• Score > 4 — PE likely. Consider diagnostic imaging.
• Score 4 or less — PE unlikely. Consider D-dimer to rule out PE.

Recommendations for a diagnostic algorithm were published by the PIOPED investigators; however, these recommendations do not reflect research using 64 slice MDCT.^[36] These investigators recommended:

• Low clinical probability. If negative D-dimer, PE is excluded. If positive D-dimer, obtain MDCT and based treatment on results.
• Moderate clinical probability. If negative D-dimer, PE is excluded. However, the authors were not concerned that a negative MDCT with negative D-dimer in this setting has a 5% probability of being false. Presumably, the 5% error rate will fall as 64 slice MDCT is more commonly used. If positive D-dimer, obtain MDCT and based treatment on results.

References

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• https://www.webmd.com/lung/what-is-a-pulmonary-embolism
• https://medlineplus.gov/pulmonaryembolism.html
• https://en.wikipedia.org/wiki/Pulmonary_embolism

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