A pulmonary embolism, or PE, occurs when a blood clot blocks a blood vessel in the lungs, usually after part of a venous thromboembolism has broken away and travelled through the venous circulation to the pulmonary arteries. The symptoms depend on the size and location of the clot, how much of the pulmonary circulation is obstructed, and the person's underlying cardiovascular and respiratory health. The classic symptoms are sudden difficulty breathing, chest pain that is often worse when breathing in, and sometimes coughing up blood. A PE can range from a relatively small clot producing limited symptoms to a large obstruction causing severe circulatory instability and becoming immediately life-threatening.
Sudden shortness of breath is one of the most characteristic symptoms. It may begin abruptly, occur at rest or with very little exertion, and feel different from ordinary breathlessness associated with exercise. The person may feel unable to get enough air, may breathe rapidly, or may have difficulty speaking normally because of breathlessness.
The severity does not necessarily correspond perfectly to the size of the clot because symptoms are influenced by the person's baseline lung and heart function and by how much pulmonary circulation is affected. Sudden unexplained breathlessness should therefore be taken seriously, particularly when it occurs together with chest pain, a rapid heartbeat, faintness or other features suggestive of venous thrombosis.
Chest pain associated with pulmonary embolism is commonly described as sharp or stabbing and may become worse during a deep breath or coughing because the clot can irritate tissues around the affected pulmonary circulation. This pattern is sometimes called pleuritic chest pain. Not every PE causes this type of pain, however; some people have more general chest discomfort, pressure or no prominent chest pain. Because chest pain has many possible causes, its presence cannot establish PE by itself. Cardiac disease, pneumonia, pneumothorax, pleurisy, musculoskeletal conditions and other disorders can produce overlapping symptoms, so clinical assessment is needed to distinguish them.
Cough can occur with pulmonary embolism, and some people cough up blood, a symptom called haemoptysis. Blood may appear as streaks or spots mixed with mucus, although more substantial bleeding can occur. Coughing up blood has many possible causes, including respiratory infection, bronchitis, pneumonia, bronchiectasis and lung cancer, but it can also occur with a pulmonary embolism. The combination of haemoptysis with sudden breathlessness, chest pain, a very fast heartbeat or faintness is particularly concerning. NHS guidance recommends emergency assessment when coughing up blood is accompanied by difficulty breathing, a very fast heartbeat or chest or upper-back pain.
Other symptoms can result from the effect of a PE on circulation. A person may develop a rapid heartbeat, dizziness, fainting or a feeling of impending collapse. A large pulmonary embolism can sharply increase resistance within the pulmonary circulation, placing strain on the right side of the heart and potentially reducing the amount of blood reaching the left side of the heart and the rest of the body. Severe cases can consequently produce low blood pressure, shock, loss of consciousness and cardiac arrest. Fainting or severe circulatory symptoms are therefore especially serious manifestations rather than merely more intense versions of ordinary breathlessness.
Because most pulmonary emboli originate from deep-vein thrombosis, symptoms in a leg can accompany respiratory symptoms. A DVT may cause pain, tenderness, swelling, warmth or redness in one leg, commonly affecting the calf or thigh. The absence of leg symptoms does not exclude PE, because the clot may have detached before obvious DVT symptoms developed or the remaining clot may not produce noticeable local symptoms. Conversely, isolated leg swelling does not prove that a pulmonary embolism has occurred. The significance comes from the overall clinical picture and the presence of risk factors such as recent surgery, prolonged immobility, hospitalisation, previous venous thromboembolism, certain cancers, pregnancy or use of oestrogen-containing medicines.
A pulmonary embolism can resemble several other acute illnesses, which is why diagnosis cannot safely be based solely on symptoms. Doctors may assess clinical probability and then use investigations such as D-dimer testing, computed tomography pulmonary angiography, ventilation-perfusion scanning, electrocardiography, blood tests and sometimes ultrasound of the legs. The purpose of these investigations is to establish whether a clot is present and to determine its physiological significance. Symptoms such as sudden breathlessness and chest pain are important warning signs, but neither symptom is specific enough to diagnose PE without considering alternative explanations.
Severe difficulty breathing, significant chest or upper-back pain, a very fast heartbeat or fainting require emergency medical attention because they can indicate a serious pulmonary embolism or another life-threatening condition. NHS guidance advises calling 999 or going to A&E for these severe symptoms rather than driving oneself. A suspected PE is generally assessed urgently in hospital, and anticoagulant treatment is commonly started when clinical suspicion is sufficiently high while diagnostic testing is undertaken. Early recognition and treatment are important because anticoagulants prevent existing clots from enlarging and reduce the formation of new clots.
