What is a pulmonary embolism (PE)? 

A pulmonary embolism is a sudden blockage in one of the pulmonary arteries in the lungs, typically caused by a blood clot that has travelled from the deep veins in the legs. This condition is a medical emergency because the blockage can restrict blood flow to the lungs, lower oxygen levels in the blood, and put significant strain on the heart, potentially becoming life-threatening if not treated immediately. 

What We will cover in This Article 

• The definition and biological mechanism of a pulmonary embolism 

• Why a PE is often the result of deep vein thrombosis (DVT) 

• Vital symptoms to recognize, including sudden shortness of breath and chest pain 

• Key risk factors and lifestyle triggers for blood clots 

• The diagnostic process used within the NHS and emergency departments 

• Modern treatment strategies following NICE guidelines 

Understanding Pulmonary Embolism 

A pulmonary embolism occurs when a foreign object most commonly a blood clot becomes lodged in an artery in the lung. This usually happens when a piece of a clot in a deep vein, typically in the leg, breaks off and travels through the venous system, through the heart, and into the pulmonary arteries. 

According to the National Institute for Health and Care Excellence (NICE) [NG158], pulmonary embolism and deep vein thrombosis are categorized together as venous thromboembolism (VTE). In the UK, VTE is a leading cause of hospital-related mortality, which is why clinical teams prioritise rapid assessment and treatment. When the artery is blocked, the lung tissue supplied by that artery may not receive enough blood, a condition called lung infarction, which causes pain and breathing difficulties. 

Causes and Common Triggers 

The most frequent cause of a PE is a blood clot from the leg (DVT), but other substances such as fat from the marrow of a broken bone, collagen, or even air bubbles can occasionally cause an embolism. 

Trigger Category	Specific Examples	Impact on Clot Formation
Physical Stasis	Recovery from surgery or long-haul travel.	Slows blood flow, allowing clots to form in leg veins.
Trauma/Injury	Fractures of the hip or leg.	Damaged blood vessels trigger the body’s clotting response.
Hormonal Changes	Pregnancy or Combined Oral Contraceptive.	Changes the balance of clotting factors in the blood.
Underlying Health	Active cancer or heart failure.	Increases the ‘stickiness’ of blood cells (hypercoagulability).

Symptoms and Warning Signs 

The symptoms of a pulmonary embolism can vary depending on how much of the lung is involved and the size of the clot. However, certain signs are considered red flags that require immediate medical intervention. 

Primary Symptoms 

• Shortness of Breath: This typically appears suddenly and always gets worse with exertion. 

• Chest Pain: Often feels like a sharp, stabbing pain that becomes more intense when you breathe in deeply (pleuritic pain). 

• Coughing: The cough may produce bloody or blood-streaked sputum. 

• Rapid Heartbeat: A feeling of palpitations or a racing heart (tachycardia). 

Secondary Signs 

Some patients may also experience lightheadedness, dizziness, or excessive sweating. In severe cases, a person may collapse or lose consciousness if the clot is large enough to block the main pulmonary artery. 

Differentiation: PE vs. Heart Attack 

Because both conditions involve chest pain and shortness of breath, they are often confused. However, the nature of the pain and the associated symptoms can help clinicians differentiate them. 

Feature	Pulmonary Embolism (PE)	Heart Attack (Myocardial Infarction)
Pain Quality	Sharp, stabbing, worse with breathing.	Heavy, crushing, ‘elephant on chest’ feeling.
Pain Radiation	Usually stays in the chest area.	Often radiates to the jaw, neck, or left arm.
Cough	May produce blood-streaked phlegm.	Less common; may involve a dry cough.
Leg Symptoms	Often preceded by a swollen, painful leg.	Usually no preceding leg symptoms.

NHS Emergency Management and Treatment 

If a PE is suspected, the patient is assessed using the Wells Score to determine the clinical probability of a clot. The NHS follows a strict protocol to dissolve or manage the blockage. 

1. CT Pulmonary Angiogram (CTPA): The ‘gold standard’ scan where a special dye is injected to see the blood flow in the lungs clearly 

2. Anticoagulation: Patients are immediately started on medications like Enoxaparin (injections) or DOACs (pills like Apixaban) to prevent the clot from growing and allow the body to break it down. 

3. Thrombolysis: In life-threatening cases, ‘clot-busting’ drugs are used to dissolve the blockage rapidly. 

4. Oxygen Therapy: To support the body while the lungs recover and to ensure vital organs receive enough oxygen. 

‘Effective management of a pulmonary embolism requires a high index of suspicion and rapid access to diagnostic imaging to prevent long-term complications like pulmonary hypertension,’ noted a 2024 clinical update from the British Thoracic Society. 

To Summarise 

A pulmonary embolism is a critical blockage in the lung’s blood supply, usually originating from a clot in the leg. It requires urgent medical attention to prevent damage to the lungs and strain on the heart. Recognition of sudden breathlessness and sharp chest pain is essential for a positive outcome. 

If you experience severe, sudden, or worsening symptoms, call 999 immediately. This is particularly urgent if you have difficulty breathing, chest pain, or feel faint. 

Authority Snapshot 

The information provided is based on emergency care protocols from NHS England and the National Institute for Health and Care Excellence [NICE NG158]. The content focuses on the clinical identification of VTE complications and the evidence-based treatment pathways used in UK hospitals. Dr. Rebecca Fernandez is a UK-trained physician with an MBBS and experience in general surgery, cardiology, internal medicine, gynecology, intensive care, and emergency medicine. She has managed critically ill patients, stabilised acute trauma cases, and provided comprehensive inpatient and outpatient care. In psychiatry, Dr. Fernandez has worked with psychotic, mood, anxiety, and substance use disorders, applying evidence-based approaches such as CBT, ACT, and mindfulness-based therapies. Her skills span patient assessment, treatment planning, and the integration of digital health solutions to support mental well-being.