Acute pulmonary embolism refers to a sudden obstruction in one or more arteries of the lungs,
by a lump of material, called an embolus, originated elsewhere in the body. Typically,
it is caused by a blood clot, or thrombus, that forms, most often,
in a deep vein of a lower limb. Pulmonary embolism occurs when part of this thrombus breaks off,
passes via the bloodstream to the lungs, gets stuck and blocks pulmonary arteries. Rarely,
an embolism can be caused by air bubbles, cancer cells, or fat tissue from a broken bone.
Risk factors include disorders that promote blood clotting, heart diseases,
cancers, recent surgeries, extended periods of inactivity, smoking, obesity, and pregnancy.
Common warning signs include sudden shortness of breath,
sharp chest pain that intensifies when breathing in, coughing – possibly with blood, and fainting.
Pulmonary embolism often occurs at multiple sites, and involves both lungs at once. The lower lobes
of the lungs are more commonly affected. Large emboli can block the main pulmonary
artery that branches to the 2 lungs, causing the so-called saddle embolism – the most fatal form.
Small emboli block small arteries, resulting in death of the downstream lung tissue,
known as pulmonary infarction. Impaired lung function leads to low oxygen levels in the blood.
Obstruction can also increase pulmonary resistance, making it harder for the
right ventricle of the heart to pump blood to the lungs. As a result, the right ventricle dilates,
bulging into the left ventricle, reducing left ventricular filling and subsequently
lowering cardiac output, which may lead to arterial hypotension and cardiogenic shock.
Prompt diagnosis and treatment are critical to reduce the high mortality
rate associated with pulmonary embolism. Diagnosis is based on symptoms, assessment
of risk factors, and a number of tests. Blood tests usually include:
- Arterial blood gas, which measures blood oxygen and carbon
dioxide level – for presence of hypoxemia. - And D-dimer test, which measures the level
of a byproduct of blood clot dissolution. A normal D-dimer value signifies a very low possibility of
pulmonary embolism, but an abnormally high D-dimer level is not enough to confirm the condition.
Imaging options include: - Chest X-ray, which is usually
normal in pulmonary embolism. A chest X-ray is performed to rule out other lung conditions that
may produce similar symptoms. A sudden low blood oxygen with a normal chest X-ray indicates a high
possibility of pulmonary embolism. - CT Pulmonary Angiography,
which allows visualization of pulmonary arteries; and Ventilation-Perfusion Scan,
which maps blood flow against air flow, are the tests of choice for diagnosis.
- MRI and compression ultrasonography are less sensitive and typically
used when radiation must be avoided. - Pulmonary angiogram, which involves
insertion of a catheter into pulmonary arteries, is the most accurate way to diagnose pulmonary
embolism, but it is a high-risk procedure and usually done only as a last resort.
Treatment typically includes prompt supportive measures and anticoagulation,
to prevent new blood clotting. Anticoagulation may be initiated even before definitive diagnosis in
patients with a high clinical suspicion. Patients with contraindication to
anticoagulants may need a filter placed in the body’s major vein – the vena cava, to
prevent clots from reaching the lungs. Hemodynamically unstable patients may
require reperfusion treatment to dissolve the existing blood clots quickly. This is
typically done with clot-busting medications given intravenously, a procedure known as thrombolysis.
Patients with contraindication to thrombolysis may require surgical removal of blood clots.