What is a pulmonary embolism?

Pulmonary embolism occurs when a clot that has travelled from another part of the body blocks the blood supply to the lung. It commonly arises from a deep vein thrombosis (DVT).

Pulmonary embolism ultimately damages areas of the lung, causing reduced oxygen levels in the blood that can potentially lead to death. Therefore, it is a serious medical condition that needs prompt medical treatment.

What is an embolism?

Blood clotting is a normal bodily function that helps to prevent bleeding. Normally, blood clots form and then break down in a continuous process. Under certain conditions, the body cannot break them down, which can lead to potentially serious consequences.

A thrombus is a blood clot that partially blocks a blood vessel. An embolus occurs when this thrombus becomes dislodged from where it has formed and travels through the bloodstream until it becomes lodged in a narrower blood vessel.

Clots most commonly occur in the deep veins of the leg, causing deep vein thrombosis (DVT). Once a clot has formed in the deep veins of the leg, it has the potential to break off and travel through the bloodstream to another area of the body, commonly the lungs.


The flow of blood within the blood vessels of the circulatory system.


The process by which blood changes from a liquid to a semi-solid state, usually to seal off any sites of bleeding. This is also known as coagulation.


Pulmonary embolism is not a disease in itself, but is rather a complication from an underlying thrombosis.

Deep vein thrombosis is the most common cause of pulmonary embolism, in which a thrombus that has formed in the legs becomes dislodged and travels through the bloodstream, lodging in the lung.

How a pulmonary embolism occurs. 

Less common causes of pulmonary embolism include:

  • An air bubble in a vein;
  • A bone fracture, which can allows fragments of bone and fat to break free into the bloodstream;
  • A cancerous tumor that has broken away from a larger tumor, or;
  • Amniotic fluid from pregnancy.

Amniotic fluid

The fluid surrounding and protecting the fetus inside the uterus during pregnancy.


The flow of blood within the blood vessels of the circulatory system.


A complete or incomplete break in a bone.


A growth caused by an abnormal and uncontrolled reproduction of cells.

Risk factors

  • Smoking;
  • Older age;
  • Being inactive for long periods, especially being confined to bed due to illness;
  • Having surgery, especially abdominal surgery;
  • A family history of the condition;
  • Being overweight;
  • Having deep vein thrombosis;
  • Pregnancy;
  • Pelvic fractures and fractures of the legs, and;
  • Certain medications, such as the oral contraceptive pill.

Abdominal surgery

Any surgical procedure that involves an incision to the abdomen.

Signs and symptoms

Pulmonary embolism may not necessarily cause any symptoms. When symptoms do occur, they may vary depending on the size, number and location of the clots and the underlying health of the person's lungs.

Some more typical signs and symptoms may include:

  • Breathlessness;
  • Chest pain;
  • Coughing up blood;
  • Mild fever;
  • Fast heart rate;
  • Low blood pressure, and;
  • Loss of consciousness.

Signs and symptoms of a deep vein thrombosis include:

  • Leg pain or tenderness;
  • Warm skin on the leg;
  • Red or blue discoloration of the skin, and;
  • Swelling in one leg.

Blood pressure

The pressure the blood places on the walls of the arteries, largely mirroring the contraction of the heart, and consisting of two readings. The higher reading is systolic blood pressure, when the heart contracts, and the lower is diastolic blood pressure, when the heart is relaxed.

Methods for diagnosis

Diagnosis of pulmonary embolism is based on a person's symptoms, medical history and a range of scans and tests, including:

  • Ventilation-perfusion scan (V/Q) scan - this test uses a very small amount of a radioactive substance to examine the lungs for a pulmonary embolism. The test involves two scans - the ventilation and perfusion scans. The ventilation scan assesses the flow of air in and out of the lungs, while the perfusion scan assesses the blood flow within the lungs. A difference between the scans may be suggestive of a pulmonary embolism. The main benefit of this test is that there is no risk of radiation exposure;
  • Computerized tomography (CT) scan - to assess the blood vessels of the lungs. This test can accurately diagnose pulmonary embolism; however, there is the small risk of radiation exposure;
  • Ultrasound of leg veins - to check for the presence of deep vein thrombosis;
  • Echocardiography - a useful diagnostic tool to assess the strain on the heart from pulmonary embolism, and;
  • D-dimer - this is a blood test that detects the by-products of a blood clot. A negative test can help rule out both deep vein thrombosis and pulmonary embolism.

Computerized tomography

A scan that uses X-rays to create a 3D image of the body. This can detect abnormalities more effectively than a simple X-ray can.


The procedure in which ultrasound waves are used to create an image of the heart, to allow assessment of the heart's function as it beats.


Energy that is emitted, such as heat, light, or energy in electromagnetic waves. Different types of radiation can be used to diagnose and treat disease.

Types of treatment

Anticoagulant therapy

The main treatment for pulmonary embolism is anticoagulant therapy - medication to stop further blood clots from developing. This type of medication does not break down existing clots, but it does stop an existing clot from getting bigger. The body can then eventually break down the clot.

Anticoagulant therapy is usually prescribed for several months, although some people may need to stay on it permanently. Anticoagulant therapy can be taken as an injection (known as clexane), or as oral medication such as warfarin.

Thrombolytic therapy

In some cases, treatment may also involve thrombolytic therapy, which is the removal of the clot, usually using a type of medication. Thrombolytic medication breaks up the blood clot, but has a risk of unwanted bleeding, especially into the brain that could cause a hemorrhagic stroke. Therefore, it is generally given only when the person is seriously unwell from pulmonary embolism.

Vena cava filter

Another form of treatment may involve the insertion of a filter, via a thin tube, into a large blood vessel that returns blood from the body to the heart, referred to as the inferior vena cava. These filters stop further blood clots from reaching the lungs and are useful when anticoagulant therapy is not suitable. It is removed once there is no longer the risk of further clots.


Some more serious cases of pulmonary embolism may require surgical removal of the embolus from the lung. This is generally reserved for very large clots, or where the person is seriously unwell.

Potential complications

Complications from pulmonary embolism can include:

  • Heart failure;
  • Pulmonary hypertension - where the blood pressure in your lungs and right side of the heart is too high, which means the heart has to work harder to push blood through these vessels;
  • Recurrent pulmonary embolisms, and;
  • Death from cardiac arrest, in which the heart stops working.

Blood pressure

The pressure the blood places on the walls of the arteries, largely mirroring the contraction of the heart, and consisting of two readings. The higher reading is systolic blood pressure, when the heart contracts, and the lower is diastolic blood pressure, when the heart is relaxed.


If pulmonary embolism is treated quickly, most people will make a full recovery. But when there is a large embolus, it may be life-threatening.


Given the link between deep vein thrombosis and pulmonary embolism, prevention needs to focus on ways to prevent deep vein thrombosis, including the following:

  • When travelling, exercising the calf and foot muscles regularly, avoiding alcohol and drinking plenty of water to avoid dehydration;
  • Maintaining a healthy weight;
  • Stopping smoking;
  • Getting regular exercise;
  • Wearing special compression stockings, if at risk of developing deep vein thrombosis, and;
  • For people having surgery or being confined to bed for long periods, being assessed for their risk of developing a deep vein thrombosis and, if necessary, taking preventative anticoagulant therapy after surgery.

FAQ Frequently asked questions