Pulmonary Embolism

Question 1

Define embolism

Answer 1

Blockage of a vessel by a solid, liquid or gas at a site distant from its origin

Question 2

List the possible material that can be embolised

Answer 2

Thrombus, tumour, air, fat, amniotic fluid, bullet

Question 3

What are risk factors for PE

Answer 3

• Age
• Surgery > 30 minutes
• Obesity
• Cancer
• Prolonged immobilisation
• Previous thromboembolism
• Heart failure
• Contraceptive pill
• Pregnancy
• Long haul travel > 4 hours
• Thrombophilia

Question 4

Explain the pathophysiology of PE

Answer 4

1. Right ventricular over load
   
   • Pulmonary artery pressure increases if more than 30% of the total cross section of the pulmonary arterial bed is occluded
   • Leads to right ventricular dilation and strain
     
     • Right ventricle has thinner walls - more susceptible to strain
   • Inotropes are released in an attempt to maintain systemic blood pressure
     
     • Cause pulmonary artery vasoconstriction - further increase pressure in right ventricle
2. Respiratory failure
   
   • Due to areas of ventilation perfusion mismatch and low right ventricle output
3. Pulmonary infarction
   
   • Small distal emboli can create areas of alveolar haemorrhage resulting in haemoptysis (coughing out blood), pleuritis, and small pleural effusion

Question 5

Describe how embolitic strokes can occur

Answer 5

• Some patients have right to left shunting through a patent foramen ovale (hole between the atrium of the heart )
  
  • May lead to severe hypoxaemia and an increased risk of paradoxical embolization and stroke
• Embolus can move through foramen ovale into brain - stroke

Question 6

Define a saddle embolus

Answer 6

Large thrombo-emboli that straddles pulmonary trunk and blocks both sides of circulation

Question 7

State the common symptoms of PE

Answer 7

• Dyspnoea (difficult breathing)
• Pleuritic chest pain
• Cough
• Substernal chest pain
• Fever
• Haemoptysis
• Syncope
• Unilateral leg pain

Question 8

What are some physical signs of PE

Answer 8

• Pleural rub in cases of pulmonary infarction

- Raised JVP

Question 9

Outline how PE can be seen on CXR, ECG and D-dimer tests

Answer 9

• Chest x-ray - by far the commonest finding in PE is a normal CXR
  
  • CXR may be done to exclude other diagnoses - pneumonia, pneumothorax
• ECG - may show signs of right ventricular strain
  
  • T wave inversion in the right precordial leads (V1-V4 and the inferior leads)
  • Classic finding - S1, Q3, T3
• Blood gases - may show hypoxaemia and hypocapnia due to hyperventilation
• D-dimer - a normal D-dimer effectively rules out PE in those at low likelihood of having a PE
  
  • In those at high likelihood, the negative predictive value of D-dimer is too low to use
  • D-dimer is a fibrin degradation product - small protein fragment released into the blood when a thrombus is degraded by fibrinolysis
  • D-dimers not normally present in the blood except when the coagulation system has been activated

Question 10

What imaging techniques can be used to investigate PE

Answer 10

• Chest x-ray
• CT pulmonary angiography (CTPA)
  
  • Dye injected into pulmonary arteries and see where blockage occurs
• Ventilation perfusion scan
  
  • Inhalation of dye can see areas of the lung which are ventilated
  • IV injection of labelled albumin can see which areas are perfused
    
    • Determine areas of ventilation perfusion mismatch

Question 11

What immediate treatment should be given to PE patients

Answer 11

• Give oxygen
• Immediate heparinisation
  
  • Stops thrombus propagation in the pulmonary arteries and allows the body’s fibrinolytic system to lyse the thrombus
  • Stops thrombus propagation at the embolic source and reduces the frequency of further pulmonary embolism
  • Not thrombolytic!

Question 12

What further treatment can be give to high risk PE patients

Answer 12

• Haemodynamic support
• Respiratory support
• Exogenous fibrinolytics (streptokinase/tPA)
  
  • Peripheral intravenous
  • Delivered directly via a percutaneous catheter into the pulmonary arteries
• Percutaneous catheter directed thrombectomy
• Surgical pulmonary embolectomy

Question 13

What further treatment is done after initial heparinisation

Answer 13

• Patients are started on an oral anticoagulant (eg. Warfarin)
  
  • For 3 months, there is an identifiable ‘temporary’ risk factor (50%)
  • Indefinitely if cancer or no identifiable risk factor (50%)
• For patients who cannot be safely anticoagulated
  
  • Occurs for patients with oesophageal varices, previous haemorrhagic stroke, severe thrombocytopenia
  • Inferior venal cava filter inserted through jugular vein
  • Prevent clot from reaching heart by acting as an umbrella which opens in the inferior vena cava after insertion