Pulmonary Embolism

• Pulmonary embolism (PE) describes a blood clot (thrombus) in the pulmonary arteries
• An embolus is a thrombus that has travelled in the blood, often from a deep vein thrombosis (DVT) in a leg
• The thrombus will block the blood flow to the lung tissue and strain the right side of the heart
• DVTs and PEs are collectively known as venous thromboembolism (VTE)
• Risk Factors for DVT or PE

  • Immobility
  • Recent surgery
  • Long-haul travel
  • Pregnancy
  • Hormone therapy with oestrogen
  • Malignancy
  • Polycythaemia
  • Systemic lupus erythematosus
  • Thrombophilia
• TOM TIP: 'In your exams, when a patient presents with possible features of a DVT or PE, ask about risk factors such as periods of immobility, surgery and long-haul flights to score extra points'
• VTE Prophylaxis


  1. Every patient admitted to hospital is assessed for their risk of venous thromboembolism (VTE)

  2. Higher-risk patients receive prophylaxis with low molecular weight heparin (e.g., enoxaparin) unless contraindicated

  3. Contraindications include active bleeding or existing anticoagulation with warfarin or a DOAC

  4. Anti-embolic compression stockings are also used unless contraindicated (e.g., peripheral arterial disease)
• Presentation of Pulmonary Embolism

  1. Pulmonary embolism can be asymptomatic (discovered incidentally), present with subtle signs and symptoms, or even cause sudden death

  2. A low threshold for suspecting a PE is required

  3. Presenting features include: Shortness of breath, Cough, Haemoptysis (coughing up blood), Pleuritic
• Pulmonary embolism


  • Can be asymptomatic, present with subtle signs and symptoms, or cause sudden death
  • Shortness of breath
  • Cough
  • Haemoptysis (coughing up blood)
  • Pleuritic chest pain (sharp pain on inspiration)
  • Hypoxia
  • Tachycardia
  • Raised respiratory rate
  • Low-grade fever
  • Haemodynamic instability causing hypotension
  • Signs and symptoms of deep vein thrombosis such as unilateral leg swelling and tenderness
• PERC Rule


  • The pulmonary embolism rule-out criteria (PERC) are recommended by the NICE guidelines (2020) when the clinician estimates less than a 15% probability of a pulmonary embolism to decide whether further investigations for a PE are needed. If all the criteria are met, further investigations for a PE are not required
• Wells Score


  • The Wells score predicts the probability of a patient having a PE. It is used when PE is suspected and accounts for risk factors and clinical findings
• Diagnosis of pulmonary embolism

  A chest x-ray is usually normal but required to rule out other pathology. The Wells score is used to decide the next step: Likely - perform a CT pulmonary angiogram (CTPA) or alternative imaging; Unlikely - perform a d-dimer, and if positive, perform a CTPA
• 1. dimer


  • A sensitive (95%) blood test for VTE that helps exclude VTE where there is low suspicion. It is almost always raised if there is a DVT. Other conditions can cause a raised d-dimer such as pneumonia, malignancy, heart failure, surgery, pregnancy
• Imaging options for pulmonary embolism diagnosis

  • CT pulmonary angiogram (CTPA), Ventilation-perfusion single photon emission computed tomography (V/Q SPECT) scan, Planar ventilation–perfusion (VQ) scan
• CT pulmonary angiogram (CTPA)

  A chest CT scan with an intravenous contrast that highlights the pulmonary arteries to demonstrate any blood clots. It is the first-line imaging for pulmonary embolism, readily available, provides a more definitive assessment, and gives information about alternative diagnoses
• Ventilation-perfusion (VQ) scan


  Involves using radioactive isotopes and a gamma camera to compare ventilation with perfusion of the lungs. Used in patients with contraindications to CTPA
• Planar V/Q scan


  Produces 2D images
• V/Q SPECT scan


  Produces 3D images, making them more accurate
• TOM TIP: 'Patients with a pulmonary embolism often have respiratory alkalosis on an ABG. Hypoxia causes a raised respiratory rate. Breathing fast means they “blow off” extra CO2. A low CO2 means the blood becomes alkalotic. The other main cause of respiratory alkalosis is hyperventilation syndrome. Patients with PE will have a low pO2, whereas patients with hyperventilation syndrome will have a high pO2'
• Management of pulmonary embolism

  Depends on the severity of symptoms and the clinical presentation
• Main causes of respiratory alkalosis

  1. Hyperventilation syndrome

  2. Pulmonary embolism (PE)
• Patients with PE will have a low pO2
• Patients with hyperventilation syndrome will have a high pO2
• Supportive management for respiratory alkalosis

  1. Depends on the severity of symptoms and clinical presentation

  2. Includes: Admission to hospital if required, Oxygen as required, Analgesia if required, Monitoring for any deterioration, Anticoagulation as the mainstay of management
• Anticoagulation management for PE

  1. NICE (2020) recommend treatment-dose apixaban or rivaroxaban as first-line

  2. Low molecular weight heparin (LMWH) is the main alternative

  3. Immediate start of LMWH in suspected PE with delayed diagnosis confirmation
• Management of Massive PE with haemodynamic compromise

  Continuous infusion of unfractionated heparin and considering thrombolysis
• Thrombolysis


  1. Injecting a fibrinolytic medication that rapidly dissolves clots

  2. Significant risk of bleeding, used in massive PE where benefits outweigh risks

  3. Examples of thrombolytic agents: streptokinase, alteplase, tenecteplase

  4. Can be performed intravenously or via catheter-directed thrombolysis
• Options for long-term anticoagulation in VTE

  • Direct-acting oral anticoagulants (DOACs): apixaban, rivaroxaban, edoxaban, dabigatran
  • Warfarin
  • Low molecular weight heparin (LMWH)
• Target INR for warfarin when treating DVTs and PEs is between 2 and 3
• Warfarin is the first-line in patients with antiphospholipid syndrome
• LMWH is the first-line anticoagulant in pregnancy
• Continue anticoagulation for specific durations based on the cause and condition