Pulmonary Embolism

A pulmonary embolism occurs when a blood clot travels to the blood vessels in the lungs and becomes lodged inside a vessel.

Causes
Blood clots can occur anywhere in the body, but most commonly they occur in the in the deep veins of the legs. Any areas in the vein that have slowed blood flow (such as around the valves) are prone to the formation of blood clots. If the clot dislodges, then it is carried along in the bloodstream through the veins to the inferior vena cava.

The blood in the inferior vena cava then empties into the right atrium, and then into the right ventricle, and is then pumped into the pulmonary arteries. Inside the lungs the pulmonary arteries branch into smaller arteries. The blood clot then becomes lodged inside one of the pulmonary arteries.

This blocks the flow of blood through it. If blood does not flow through the artery to the capillaries, then gas exchange is prevented at the alveoli.

Risk Factors
Risk factors for a deep vein thrombosis include prolonged immobilization, recent surgery, malignancy, smoking and obesity. Women who are pregnant are also at a higher risk, as are women who take certain birth control medications. 

Signs and Symptoms
There will usually be a sudden onset of shortness of breath, and also tachycardia. There may be chest discomfort. Diagnosis is difficult as the signs and symptoms are similar to many other diseases.

A massive pulmonary embolism will cause hypotension and distended jugular veins. There will be respiratory distress and a decrease in oxygen saturations.

Investigations
Oxygen saturations should be monitored.

Chest x-ray is not usually helpful to diagnose pulmonary embolism. However it may be required to investigate for other potential respiratory diseases that have similar symptoms.

The electrocardiogram (ECG) usually shows tachycardia, sometimes with various other abnormalities. The ECG does not usually help diagnosis of pulmonary embolism, but is often ordered as it enables examination of other potential diseases that have similar symptoms.

Echocardiography (ECHO) may occasionally have abnormalities that are suggestive of pulmonary embolism.

A blood test that identifies the D-dimer level can sometimes be useful, if the laboratory is able to perform it.

Accurate diagnosis of pulmonary embolism requires advanced equipment, such as CT pulmonary angiogram (CT PA).

Treatment
Oxygen should be administered to any patient that is short of breath.

Anticoagulation is the main treatment for pulmonary embolism. The aim is to prevent recurrent clots forming.