Pulmonary embolus - blood clot to the lung - causes

[UPDATED NOVEMBER 2022]

What is a pulcomary embolus?

A pulmonary embolus occurs when blood inadvertently clots in the deep veins (not the arteries) of the leg or pelvis, the clot then becomes detached and passes up the inferior vena cava, passes through the heart and lodges in the lung. This means that one part of the lung loses its blood supply and one gets sudden onset of pain, shortness of breath and sometimes haemoptysis (coughing blood). Depending on the size of the embolus the symptoms may be very mild, or so severe as to cause death. Any patient suspected of having a pulmonary embolus must be admitted to hospital as an emergency for proper investigation by ventilation perfusion scan, and urgent anti-coagulation.

Many minor pulmonary emboli go undiagnosed, which is of course a dangerous situation because having one pulmonary embolism is obviously a risk factor for further ones.

Causes of pulmonary embolus

Pulmonary emboli start with blood clots in the veins of the leg which may result from

• Pro-thrombotic tendency see Blood clotting problems and Veins, lymphatics, swollen ankles, phlebitis and venous thrombosis
• Smoking
• Pill and HRT - see The serious complications of taking the Pill and HRT
• Lack of mobility,
• Enforced bed rest for any reason for example following a general anaesthetic, hospital inpatient stay.
• Enforced rest for any reason such as air travel
• Hip, or pelvic surgery
• Dehydration
• Possibly allergies
• Pregnancy
• Cancer - a so called non-metastatic effect of cancer may be a deep vein thrombosis

Symptoms of a deep vein thrombosis (DVT)

Typically the lower leg (and it's one leg not two) is hot, red, painful and swollen with pitting oedema (leaves a thumbprint). Stretching the calf muscle causes pain. The blockage of the vein is not serious - the problem arises if the clot becomes dislodged and travels in the blood stream to the lungs where it gets stuck to cause a pulmonary embolus.

What clinically looks exactly like a DVT is a ruptured Baker's cyst. This is a ganglion at the back of the knee which bursts and its irritant contents track down into the muscle of the lower leg causing it to become acutely inflammed.

A thrombosis in an artery cuts off the blood supply to the leg so it becomes painful, white and cold with no pulses in the foot. Usually teh lge is not swollen.

Related Articles

• Blood clotting problems
• Veins, lymphatics, swollen ankles, phlebitis and venous thrombosis
• The serious complications of taking the Pill and HRT

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