A sudden obstruction of pulmonary circulation; lodging of a blood clot in the pulmonary arterial tree with subsequent increase in pulmonary vascular resistance and possible obstruction of blood supply to the lung parenchyma.

Causes:
- blood clot embolization from deep pelvic or leg veins
- fat embolism (related to fractured femur or pelvis), air embolus

Risk factors:
- prolonged bed rest
- advanced age
- obesity
- lower limb trauma
- oral contraceptives
- recent surgery
- stroke
- pregnancy
- congestive heart failure
- malignant disease

Symptoms vary greatly in severity. Pulmonary embolus may present as three different syndromes.
- acute cor pulmonale (right-sided heart failure) due to massive embolus obstructing 60% to 75% of the pulmonary circulation
- pulmonary infarction, which occurs in patients with massive embolism and complete obstruction of a distal branch of the pulmonary circulation
- acute unexplained shortness of breath, which occurs in patients who do not have cor pulmonale or infarction
- sudden onset of shortness of breath (may be the only symptom)
- pleuritic chest pain with infarction
- cough (rare)
- hemoptysis may be present in infarction
- syncope (faintness) may be present in cor pulmonale
- leg pain (infrequent)
- anxiety
- older clients may present with increasing shortness of breath, confusion, and restlessness (which indicate hypoxia)

Physical findings are variable. The results of the examination can be deceptively normal or obviously abnormal. Consider pulmonary embolism in any person with unexplained dyspnea. Physical findings may include:
- heart rate elevated
- respiratory rate elevated
- blood pressure normal, elevated or low (cor pulmonale)
- mild-to-severe respiratory distress, oxygen saturation decreased
- anxiety
- sweating, pallor and cyanosis may be present
- distension of neck veins with cor pulmonale
- peripheral edema may be present with cor pulmonale
- swelling, redness of calf infrequently present
- calf tenderness may be present
- peripheral pitting edema may be present
- dullness to percussion may be present (with infarction and if associated with pleural effusion)
- air entry may be reduced in affected area
- crackles and wheezes may be present (with infarction)
- S3 (gallop rhythm) may be present with cor pulmonale
- loud second heart sound may be present

See more information at the reference.

Adapted from Clinical Practice Guidelines for Nurses in Primary Care. Respiratory System. Internet. Accessed on August 31, 2009.