Pulmonary embolism (PE)

A pulmonary embolism is a blockage of an artery in the lung by a blood clot that has travelled there through the veins, almost always from the deep veins of the calf, thigh or pelvis. Part of the lung stops receiving blood, and the right side of the heart has to push blood through a narrowed channel; with a large clot it may fail within minutes. The outcome depends above all on how quickly someone reaches hospital, which is why this page starts with the warning signs rather than the causes.

Signs that mean calling an ambulance

Call an ambulance — in Spain, Italy, Portugal, Poland and Ukraine the single European number is 112 — or go straight to an emergency department if any of these come on suddenly:

• breathlessness that develops within minutes for no obvious reason;
• pain in the chest or between the shoulder blades that is worse when you breathe in and makes you breathe shallowly;
• coughing up blood;
• a very fast heartbeat that will not settle;
• fainting, or everything going dark when you stand up;
• blue lips, cold sweat, sudden weakness.

Do not drive yourself. People can lose consciousness on the way. If you can, take a list of your medicines with you: the first thing the team needs to know is whether any of them thin the blood.

The leg deserves a separate mention. Swelling in one calf only, a tight bursting ache, and skin that is warmer and redder than on the other leg are signs of deep vein thrombosis — the very source from which a clot travels to the lungs. This should not wait: see a doctor the same day, even if your breathing feels normal.

Why it is so easily missed

The textbook picture — sudden breathlessness, pain on breathing in, blood in the sputum — is complete in only a minority. Most people never cough up blood at all, and pain appears only when the blocked vessel lies near the edge of the lung and the pleura becomes irritated.

Small clots produce vague complaints: breathlessness climbing a flight of stairs that was not there before, unexplained tiredness, a dry cough, a slightly raised temperature, restlessness with no cause. These are often put down to a chest infection, anxiety or being out of condition. In older people the first and only event may be a faint or sudden confusion. In someone who already has heart or lung disease, a pulmonary embolism disguises itself as the usual flare-up — except that this time things got worse faster and the usual treatment is not helping.

All the versions share one feature: the change was abrupt. Breathlessness that has built up over six months points to other conditions. Breathlessness that started yesterday or this morning needs an answer today.

Where the clot comes from and what encourages it

The clot nearly always forms in the veins of the legs or pelvis, breaks free and passes through the right side of the heart into the pulmonary arteries. Deep vein thrombosis and pulmonary embolism are therefore not two separate illnesses but two stages of one process.

Blood clots where it pools, where the vessel wall is damaged, or where clotting itself is increased. Hence the list of circumstances:

• prolonged immobility: bed rest, a plaster cast, a flight or journey of more than four hours, work that keeps you seated for half a day;
• surgery, particularly on joints, the pelvis and the abdomen, and the first weeks afterwards;
• a fractured leg or hip, or serious injury;
• pregnancy and, above all, the first six weeks after giving birth — the period of highest risk in a woman's life;
• combined hormonal contraceptives and hormone replacement therapy;
• cancer and chemotherapy; sometimes a clot is the first sign of a tumour that has not yet been found;
• inherited thrombophilia and antiphospholipid syndrome, suspected when a clot occurs young, recurs, appears with no trigger at all, or has already happened to close relatives;
• a previous clot or pulmonary embolism;
• severe infection with bed rest, heart failure, inflammatory bowel disease;
• substantial excess weight, smoking, dehydration.

These factors add up. A flight on its own rarely causes trouble, but a flight a month after knee surgery, or while taking combined contraceptives, is a different matter.

How the diagnosis is confirmed

No single symptom either proves or rules out a pulmonary embolism, so the doctor first works out the probability from the whole picture — complaints, circumstances and examination — and the order of tests follows from that.

• D-dimer, a blood test for clot breakdown products. Its value lies the other way round: a normal result in someone at low probability allows the diagnosis to be set aside with confidence. A raised result proves nothing, since it rises with inflammation, injury, tumours, pregnancy and simply with age.
• CT pulmonary angiography with contrast — the main test, because it shows the clot directly.
• Ventilation-perfusion scanning — used where contrast is unsuitable: in pregnancy, in severe kidney failure, or with contrast allergy.
• Ultrasound of the leg veins — looks for the source; finding a clot alongside the right symptoms effectively settles the question.
• Echocardiogram — shows how strained the right side of the heart is. It shapes the treatment plan rather than the diagnosis itself.
• An ECG, a chest X-ray and blood tests are used mainly to exclude a heart attack, pneumonia or a collapsed lung.

Where suspicion is strong, treatment begins before the scan: delay is more dangerous than one unnecessary dose of anticoagulant.

What happens in hospital and afterwards

Anticoagulants are the mainstay. They do not dissolve a clot that has already formed: they stop it growing and prevent new ones, while the body gradually clears what is there. Treatment usually starts with injections or with direct-acting tablets and continues as long-term tablets.

When an embolism is massive and blood pressure drops, thrombolysis is used — a drug that dissolves the clot. Sometimes it is delivered straight into the pulmonary artery through a catheter, and in rare cases the clot is removed surgically. A vena cava filter is fitted only occasionally, mainly for people who cannot take anticoagulants.

Tablets are taken for at least three months, and whether to continue depends on the cause. If the embolism followed an operation or a fracture — a clear trigger that has now passed — the course usually has an end date. If no trigger was found, if this is a second episode, or if there is a thrombophilia or an active cancer, treatment is often continued for years.

While you are on an anticoagulant, three things matter: do not miss doses or stop on your own, because the risk returns quickly; tell every doctor and your dentist before any procedure; and seek help at once for unusual bleeding, black stools, vomiting blood, or after a blow to the head. One more point: everyday anti-inflammatory painkillers raise the risk of stomach bleeding when combined with an anticoagulant, so it is worth asking which painkiller to use.

If breathlessness lasts for months

It is often said that a pulmonary embolism treated in time leaves no trace. That is true for most people, but not all: some notice six months later that stairs are harder than before the illness, that they tire quickly, and that they cannot get back to what they used to do. This is not imagination or nerves after a frightening event. Persistent breathlessness has measurable causes, and they are worth looking for.

Most often it is general deconditioning after illness combined with an understandable fear of exertion, and gradual supervised rehabilitation helps. But in a small proportion of people the clots that never dissolved turn into scar tissue that permanently narrows the pulmonary arteries. This is chronic thromboembolic pulmonary hypertension, and the key point about it is this: it can be treated, and in some cases surgery removes it altogether and restores normal breathing.

So breathlessness that is still there three to six months after a pulmonary embolism should not simply be endured: see a doctor and ask about an echocardiogram. If suspicion remains, the next steps are a perfusion scan and right heart catheterisation at a specialist centre. The earlier this is clarified, the more surgical options stay open.

What lowers the risk

• After an operation or during an illness spent in bed, get up and walk as early as your doctor allows; hospitals usually offer preventive injections or compression stockings, and these are worth accepting.
• On long journeys, get up and walk every hour or so, and while seated flex and stretch your ankles, drink water and go easy on alcohol and coffee.
• Compression stockings on flights make sense for anyone who has had a clot before, has varicose veins or has recently had surgery.
• If you take combined contraceptives, say so before planned surgery and before any long period of immobility: the plan is sometimes changed.
• Keep moving regularly, keep your weight within a reasonable range and do not smoke.
• Know your own history: a previous clot in you or in close relatives is information to give before a procedure, not after it.

Online consultation

An online consultation is not a substitute for the emergency services: sudden breathlessness, chest pain on breathing in, coughing up blood or fainting all need an emergency call, not a message to a doctor. It is genuinely useful, though, for everything that surrounds this illness before and after.

It is worth booking one if you have noticed swelling and pain in one calf and are unsure how urgent it is; if you have a long flight or an operation coming up and there has been a clot in you or your family; if you take an anticoagulant and do not know what to do about a missed dose, a trip or a dental extraction; or if breathlessness has persisted for months after an embolism and you do not know who to turn to.

Have your discharge summary to hand, along with the names and doses of your medicines and the results of recent blood tests and scans. The doctor will explain which investigations are genuinely needed, help you make sense of the regimen you have been given, and point you towards the right specialist. If anything in your account suggests an emergency, you will be directed there straight away.

This material is for information only and does not replace medical advice.