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Pulmonary embolism - symptoms, diagnosis, treatment, prevention


Pulmonary embolism is a blockage of a pulmonary artery in the lungs. It is a serious medical condition. Prompt diagnosis and treatment reduces the risk of complications and death. Preventing pulmonary embolism will focus on preventing or treating blood clots formed in veins in the legs or other parts of the body (deep vein thrombosis).

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.  

Causes

Pulmonary embolism is usually caused by a blood clot becoming lodged in a pulmonary artery. A pulmonary artery is a major blood vessel that supplies blood to the lungs from the heart. Multiple clots are often involved but not always at the same time.

These 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 clots in the veins is known as deep vein thrombosis (DVT).

Sometimes, substances other than a blood clot are responsible for pulmonary embolism. A bubble of air or other gas, collagen or other type of tissue, tumour fragment, or fat globule from the marrow of a broken bone can travel in the bloodstream to the lungs where they can also cause pulmonary embolism.

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 certain factors, including:

Personal and family history

  • Having had a previous 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. Clots are more likely to form when blood slows or pools.

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 for long periods of time causes the flow of venous blood to slow and to pool in the legs. Similarly, sitting for an extended duration also results in reduced venous blood flow and the pooling of blood in the lower legs. Slow blood flow or the pooling of blood encourages clot formation.

Medical conditions and treatments

  • Cardiovascular disease, mainly heart failure
  • Cancer, especially pancreatic, ovarian, lung cancer, cancers with metastasis
  • 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
  • Supplemental oestrogen, ie: birth control pills and hormone replacement therapy
  • Chemotherapy and radiotherapy
  • Thrombophilia
  • Antiphospholipid syndrome
  • Vasculitis.

Any medical condition or treatment that increases levels of substances that cause blood to clot or that damages the inside surface of blood vessels, which also makes blood more prone to clotting, increases the risk of pulmonary embolism.

Complications

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.

As pulmonary embolism can be life-threatening, immediate medical attention should be sought if unexplained shortness of breath, chest pain, or a cough that produces blood are experienced.

Diagnosis

Pulmonary embolism can be difficult to diagnose because some people have no obvious symptoms while in others symptoms are non-specific. 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 the clot-dissolving substance, D dimer, which 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
Ultrasound uses sound waves that bounce off blood vessels, which are then converted by a computer into images. Duplex ultrasonography is a type of ultrasound 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
This type of CT scan involves a scanner rotating around the body in a spiral to create 3-D images. Spiral CT can detect abnormalities within lung arteries with high precision. Contrast material may be administered by injection into a vein (ie: intravenously) during the CT scan to enhance the outline of the pulmonary arteries.

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-rays are then taken, which assess the flow of blood and air through the lungs. Abnormalities may suggest a pulmonary embolism.

Pulmonary angiogram
A pulmonary angiogram is the most accurate way to diagnose pulmonary embolism. 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, thus providing a clear picture of the blood flow.
Pulmonary angiogram is usually performed when other tests fail to provide a definitive 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 involves the use of radio waves and a magnetic field to produce detailed images of the inside of the body. 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.

Treatment

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.

Medications

Anticoagulants (‘blood thinners’): These drugs stop new clots from forming. Heparin, which is given by injection, is a commonly used anticoagulant. Because heparin acts quickly, it is used at the same time as an oral anticoagulant (eg: warfarin), which can take several days to becomes effective. A newer class of oral anticoagulants, novel oral anticoagulants (NOACs, eg: rivaroxaban), work more quickly than warfarin and have fewer interactions with other medications. Some NOACs can be given without the need for overlap with heparin. All anticoagulants have side effects, with bleeding being the most common.

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 via a catheter that is threaded through blood vessels to the site of the clot.

Vein filter: Using a catheter, a small filter that traps any clots and prevents them from reaching the lungs is positioned in the main vein leading to the heart (the inferior vena cava). 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.

Prevention

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 use of a therapeutic device comprising inflatable thigh-high or calf-high cuffs that rhythmically 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 help 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.

References

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 (2016). Pulmonary embolism (Web Page). Rochester, MN: Mayo Foundation for Medical Education and Research. http://www.mayoclinic.org/diseases-conditions/pulmonary-embolism/home/ovc-20234736 [Accessed: 10/07/16]
Ourellette, D.R. (2016). Pulmonary embolism (Web page). Medscape Drugs and Diseases. New York, NY: WebMD LLC. http://emedicine.medscape.com/article/300901-overview [Accessed: 23/01/17].
O’Toole, M.T. (Ed.) (2013). Pulmonary embolism (PE). Mosby’s Dictionary of Medicine, Nursing & Health Professions (9th ed.). St Louis: Elsevier Mosby.

Created: March 2017

 

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