Southern Cross Medical Library

Southern Cross Medical Library

Pulmonary embolism occurs when an artery in the lungs becomes blocked, in most cases by blood clots that travel to the lungs from elsewhere in the body.

Prompt diagnosis and treatment reduces the risk of serious medical complications and death.

It has been estimated that each year approximately one in every 3,500 New Zealanders will develop a pulmonary embolism. Of the people who develop a pulmonary embolism, 10% die within the first hour and 33% die subsequently from recurrent embolism.


Pulmonary embolism is usually caused by a blood clot (a solid clump of blood) becoming lodged in an artery that supplies blood to the lungs. Those blood clots typically come from the deep veins of the legs, especially the calves, but may less commonly originate in other parts of the body.

The formation of a clot in a deep vein is known as deep vein thrombosis (DVT). Sometimes, substances other than a blood clot are responsible for pulmonary embolism. Examples include a bubble of air, part of a tumour, or fat from the marrow of a broken bone which can travel in the bloodstream to the lungs.

Risk factors

Blood clots, and a subsequent pulmonary embolism, can develop in anyone. However, a person’s risk of pulmonary embolism can be increased by various factors, including:

Personal and family history

  • Previously having a blood clot
  • Having a family member who has had a blood clot in the past.
  • Certain inherited disorders make the blood more prone to clotting.

General factors

  • Being aged 60 years or older
  • Smoking
  • Being overweight, especially women who smoke and/or have high blood pressure
  • Pregnancy (during pregnancy, the weight of the baby pressing on veins in the pelvis can slow blood return from the legs, which leads to blood pooling in the legs).

Prolonged immobility

  • Bed rest, ie: being confined to bed after a serious illness (eg: stroke), serious injury, or after surgery
  • Long journeys, i.e.: sitting for several hours or more in a plane, train, bus, or car.
  • Lying horizontal or sitting for long periods of time causes the flow of blood to slow and to pool in the legs.

Medical conditions and treatments

  • Cardiovascular disease, mainly heart failure
  • Cancer, especially pancreatic, ovarian, lung cancer, and cancers that have spread to other parts of the body
  • Women with a personal or family history of breast cancer taking tamoxifen or raloxifene
  • Surgery, which is one of the most common causes of blood clots
  • Chemotherapy and radiotherapy
  • Thrombophilia
  • Antiphospholipid syndrome
  • Vasculitis.


Pulmonary embolism is a condition that can lead to serious complications and even death, especially if a blood clot is large or if there is more than one clot. Left undiagnosed and untreated, about one-third of cases of pulmonary embolism result in death.

Reduced blood flow to the lung tissue can lead to partial lung damage. The loss of a portion of healthy lung may make it more difficult for the lungs to supply oxygen to the rest of the body, which in turn can result in damage in other organs. The damage to lung tissue may also lead to pulmonary hypertension, which is increased pressure in the pulmonary arteries and the heart.

Blockages of the pulmonary arteries requires the heart to work harder to pump blood through the affected vessels. This causes an increase of blood pressure within the pulmonary arteries and the right side of the heart, which can weaken the heart.

Signs and symptoms

The most common signs and symptoms of pulmonary embolism are:

  • Shortness of breath that occurs suddenly and worsens with physical effort
  • Chest pain, which worsens with physical effort but does not improve with rest
  • Cough that may produce blood.

Less common signs and symptoms include:

  • Leg pain or swelling, usually in the calf
  • Clammy or discoloured skin
  • Excessive sweating
  • Fever
  • Rapid or irregular heartbeat
  • Light-headedness or dizziness.

Immediate medical attention should be sought if unexplained shortness of breath, chest pain, or a cough that produces blood are experienced.


Pulmonary embolism can be difficult to diagnose because some people have no obvious symptoms. Diagnosis is also difficult in people with underlying heart or lung disease. Pulmonary embolism is usually diagnosed by one or more of the following tests.

Blood tests

A blood test can reveal a low level of oxygen in the blood, which can be caused by a clot in a lung blood vessel, or high levels of D dimer (a natural clot-dissolving substance produced by the body) that may be increased in the presence of blood clots. A blood test can also determine whether someone has an inherited clotting disorder.

Chest x-ray

An x-ray produces film images of the heart and lungs. It cannot diagnose pulmonary embolism but can be used to exclude other causes of chest pain in patients with suspected pulmonary embolism.

Duplex ultrasound

Duplex ultrasonography is a type of ultrasound scan that measures how blood flows through arteries and veins. It is used to check for the presence of blood clots in leg veins.

Spiral computed tomography (CT) scan

Spiral CT can detect abnormalities within lung arteries with high precision. Contrast material may be injected into a vein during the CT scan to enhance the quality of the images.

Ventilation – perfusion (VQ) Scan

During a VQ scan the patient inhales a special aerosol and a special dye is injected into a vein. The aerosol and dye can be seen on x-ray as they move through the lungs. A series of x-ray images are then taken to assess the flow of blood and air through the lungs.

Pulmonary angiogram

A pulmonary angiogram is the most accurate way to diagnose pulmonary embolism. A thin flexible tube called a catheter is inserted into a large vein (usually one in the groin) and threaded through into the heart and then into the pulmonary arteries. A special dye is injected and x-rays are taken as the dye travels through the lung arteries, providing a clear picture of the blood flow. Pulmonary angiogram is usually used when other tests fail to provide a clear diagnosis. It requires a high level of skill and has potentially serious risks, eg: the dye may cause kidney damage in people with reduced kidney function.

Magnetic resonance imaging (MRI)

MRI is usually used for pregnant women (to avoid the baby being exposed to radiation) or people whose kidneys may be harmed by dyes or contrast materials that are used in other tests.


The aim of treatment for pulmonary embolism is to prevent the blood clot from getting bigger and new clots from forming. Prompt treatment is essential to prevent serious complications or death.


Anticoagulants (‘blood thinners’): These drugs stop new clots from forming. Heparin, which is given by injection, is a quick acting anticoagulant.It is usually used at the same time as an oral anticoagulant in tablet form, such as warfarin, which can be slower to take effect. All anticoagulants have side effects, including causing bleeding.

Thrombolytics (’clot dissolvers’): Clots usually dissolve on their own but this process can take time. Thrombolytic drugs, which are administered by injection, can dissolve clots quickly. However, as they can cause sudden and severe bleeding, thrombolytic drugs are usually reserved for life-threatening situations.

Surgical and other procedures

Clot removal: Large clots can be removed using a catheter tube that is threaded through blood vessels to the site of the clot.

Vein filter: A small filter that traps clots and prevents them from reaching the lungs is positioned using a catheter in the main vein leading to the heart. This procedure is usually used for people unable to take anticoagulant drugs or when the action of anticoagulant drugs is inadequate or not fast enough.


Preventing deep vein thrombosis will help to prevent pulmonary embolism. Measures to prevent blood clots forming in the legs include:

  • Giving anticoagulants to people at risk of clots before and after surgery and to people who have had a heart attack, stroke, or complications of cancer
  • Wearing elasticated compression stockings, which squeeze the legs helping the veins and leg muscles move blood more efficiently and reduce the pooling of blood in the lower legs
  • Elevating the legs when possible and during the night to help reduce blood pooling
  • Physical activity, which promotes blood circulation

Intermittent pneumatic compression, which involves using a device that massages and squeezes the veins in the legs to improve blood flow.

Prevention while traveling

The risk of blood clots developing while traveling is generally low, but the risk increases with longer duration of travel, and if you have other risk factors. The following activities can help to prevent blood clots during travel:

  • Avoid sitting for too long. If flying, move around the airplane cabin every hour and do some deep knee bends. If driving, stop every hour and walk around
  • While sitting, flex your ankles every half hour or so
  • Wear compression stockings to help promote circulation and fluid movement in the lower legs
  • Drink plenty of water to prevent dehydration, which can contribute to the formation of blood clots.


Liao, S. et al. Incidence of venous thromboembolism in different ethnic groups: a regional direct comparison study. J Thromb Haemost 2014;12:214-9.
Mayo Clinic (2020). Pulmonary embolism (Web Page). Rochester, MN: Mayo Foundation for Medical Education and Research. [Accessed: 21/01/20]
Ourellette, D.R. (2019). Pulmonary embolism (Web Page). Medscape Drugs and Diseases. New York, NY: WebMD LLC. [Accessed: 21/01/20].
O’Toole, M.T. (Ed.) (2017). Pulmonary embolism (PE). Mosby’s Dictionary of Medicine, Nursing & Health Professions (10th ed.). St Louis, MI: Elsevier.

Reviewed: February 2020


Go to our Medical Library Index Page to find information on other medical conditions.

The purpose of the Southern Cross Medical Library is to provide information of a general nature to help you better understand certain medical conditions. Always seek specific medical advice for treatment appropriate to you. This information is not intended to relate specifically to insurance or healthcare services provided by Southern Cross.