pulmonary embolism

• PE - blood clot (thrombus) in the pulmonary arteries
• an embolus is a thrombus that has travelled in the blood, often from a deep vein thrombosis in the 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
• risk factors of DVT or PE:

  • Immobility
  • Recent surgery
  • Long-haul travel
  • Pregnancy
  • Hormone therapy with oestrogen (e.g., combined oral contraceptive pill or hormone replacement therapy)
  • Malignancy
  • Polycythaemia (raised haemoglobin)
  • Systemic lupus erythematosus
  • Thrombophilia
• 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
• every patient admitted to hospital is assessed for risk of venous thromboembolism

  higher risk patients will receive prophylaxis with low molecular weight heparin unless contraindicated

  contraindications include active bleeding or existing anticoagulation with warfarin or a DOAC
• anti embolic compression stockings are used unless contraindicated eg peripheral arterial disease
• PE can be asymptomatic, present with subtle signs and symptoms or even cause sudden death

  a low threshold for suspecting a PE is required
• presenting features of a PE include:

  • 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
• there may be signs and symptoms of a deep vein thrombosis, such as unilateral leg swelling and tenderness
• wells score predicts the probability of a patient having a PE

  it is used when PE is suspected

  it accounts for risk factors eg. recent surgery and clinical findings eg. heart rate above 100 and haemoptysis
• a chest x ray is usually normal in a PE but is required to rule out other pathology
• wells score is used when considering PE - outcome decides the next step:

  • Likely: perform a CT pulmonary angiogram (CTPA) or alternative imaging (see below)
  • Unlikely: perform a d-dimer, and if positive, perform a CTPA
• D-dimer is sensitive (95%) but not a specific blood test for VTE

  it helps exclude VTE where there is a low suspicion

  it is almost always raised if there is a DVT
• other conditions that raise D-dimer:

  • Pneumonia
  • Malignancy
  • Heart failure
  • Surgery
  • Pregnancy
• there are three imaging options for establishing a diagnosis of a PE:

  • CT pulmonary angiogram (the usual first-line)
  • Ventilation-perfusion single photon emission computed tomography (V/Q SPECT) scan
  • Planar ventilation–perfusion (VQ) scan
• CT pulmonary angiogram (CTPA) is a chest CT scan with an intravenous contrast that highlights the pulmonary arteries to demonstrate any blood clots

  first line imaging for PE- readily available, provides a more definitive assessment and gives information about alternative diagnoses sucha s pneumonia
• ventilation perfusion VQ scan - uses radioactive isotopes and a gamma camera to compare ventilation with the perfusion of the lungs

  they are used in patients with renal impairment, contrast allergy or at risk from radiation, where a CTPA is unsuitable
• VQ scan - isotopes are inhaled to fill the lungs and a picture is taken to demonstrate ventilation

  a contrast containing isotopes is injected and a picture is taken to illustrate perfusion

  the two images are compared

  With a PE - there will be a deficit in perfusion as the thrombus blocks blood flow to the lung tissue - the lung tissue will be ventilated but not perfused
• planar V/Q scans produce 2D images

  V/Q SPECT scans produce 3D images - more accurate
• patients with a PE often have respiratory alkalosis on an ABAG

  Hypoxia causes a raised respiratory rate

  breathing fast means they blow off extra CO2

  a low CO2 means the blood become alkalotic

  the other main cause of respiratory alkalosis is hyperventilation syndrome

  patients with PE will have a low pO2, patients with hyperventilation syndrome will have a high pO2
• Supportive management depends on the severity of symptoms and the clinical presentation, including:

  • Admission to hospital if required
  • Oxygen as required
  • Analgesia if required
  • Monitoring for any deterioration
• Anticoagulation is the mainstay of management. In most patients, NICE (2020) recommend treatment-dose apixaban or rivaroxaban as first-line. Low molecular weight heparin (LMWH) is the main alternative. This should be started immediately in patients where PE is suspected and there is a delay in getting a scan to confirm the diagnosis
• Massive PE with haemodynamic compromise is treated with a continuous infusion of unfractionated heparin and considering thrombolysis. Thrombolysis - injecting a fibrinolytic (breaks down fibrin) medication that rapidly dissolves clots. There is a significant risk of bleeding with thrombolysis. It is only used in patients with a massive PE where the benefits outweigh the risks. Some examples of thrombolytic agents are streptokinase, alteplase and tenecteplase.
• two ways thrombolysis can be performed:

  • Intravenously using a peripheral cannula
  • Catheter-directed thrombolysis (directly into the pulmonary arteries using a central catheter)
• The options for long-term anticoagulation in VTE are a DOAC, warfarin or LMWH
• Direct-acting oral anticoagulants (DOACs) are oral anticoagulants that do not require monitoring. Options are apixaban, rivaroxaban, edoxaban and dabigatran. They are suitable for most patients. Exceptions include severe renal impairment (creatinine clearance less than 15 ml/min), antiphospholipid syndrome and pregnancy
• Warfarin is a vitamin K antagonist. The target INR for warfarin is between 2 and 3 when treating DVTs and PEs. It is the first-line in patients with antiphospholipid syndrome (who also require initial concurrent treatment with LMWH)
• Low molecular weight heparin (LMWH) is the first-line anticoagulant in pregnancy.

  Continue anticoagulation for:

  • 3 months with a reversible cause (then review)
  • Beyond 3 months with unprovoked PE, recurrent VTE or an irreversible underlying cause (e.g., thrombophilia)
  • 3-6 months in active cancer (then review)