A pulmonary thromboembolus, or pulmonary embolus (PE), begins as a thrombus, typically forming in a large leg or pelvic vein. It dislodges and travels up the inferior vena cava, through the right side of the heart, and into the main pulmonary arteries as they branch. Thrombi may form with stasis and/or inflammation or coagulopathy in the large veins in the legs and pelvis.

In health care settings with low prevalence of PE, unnecessary testing can be avoided by applying the pulmonary embolism rule-out criteria (PERC) that include:
  • age <50 years

  • pulse rate <100/min

  • SpO2 >94% (peripheral capillary oxygen saturation)

  • no unilateral leg swelling

  • no hemoptysis

  • no surgery or trauma within 4 weeks

  • no prior deep vein thrombosis or PE

  • no oral hormone use