Pulmonary Embolism(PE) is when an emboli lodges in the pumonary arterial tree.

  • Pulmonary: Lung
  • Embolism: An occlusion in the blood vessel due to a blood clot, air, fat, etc.


Pulmonary Embolism is one element of Venous Thromboembolism (VTE). VTE also includes deep vein thrombosis (DVT). Studies show that annually, there are 60-70 cases / 100 000 of PE. PE is an emergency where there is a high chance of mortality. Therefore, PE has to be always suspected if patients with any of the risk factors and symptoms. It should be managed very quickly to prevent further complications.


    Thrombus formation in the veins (e.g.DVT) is caused by three main factors known as Virchow's triad (diagram on the right).

    The most common cause of PE is from a deep vein thrombosis (DVT). This is mostly formed in the deep veins of the legs which travels through the veins up the right heart. The thrombus then lodges in the pulmonary arteries, causing a PE. Post-myocardial infarction is another cause of PE where thrombosis is formed. Therefore patients have to be carefully monitored after an MI. In addition, right sided endocarditis could cause a septic emboli.

     The reason is not clearly known but long bone fractures may also lead to fat emboli. Also, there are cases where air emboli could form from any invasive procedures such as cannulation. Intravenous drug users also occasionally present with cases of a foreign body emboli.



    Virchow's Triad


    Clinical Scenario

    A 42-year old women comes in to the A&E with shortness of breath. On questioning, she reports a sharp pleuritic chest pain. She has recently had a surgery for resection of the colon cancer. On chest examination, there was no obvious changes.

    What could it be ? (Differential Diagnosis)

    Conditions that present with chest pain or progressive shortness of breath

    • Pulmonary Embolism
    • Pneumonia
    • Myocardial Infarction
    • Pneumothorax
    • Pericarditis
    • Rib fracture
    • Dissecting Aortic Aneurysm
    • Lung Cancer
    • Tietze's Syndrome


    Consider PE when patient presents with:

    • Collapse
    • New onset atrial fibrillation
    • Unexplained breathlessness
    • Signs of right heart failure
    • Pleural effusion


      When questioning the patient, find out about risk factors.



      • Previous DVT/ PE
      • Recent surgery (Hip/knee replacement,pelvic/major abdominal surgery)
      • Recent fracture
      • Active malignancy
      • Reduced mobility(Hospitalisation)
      • Late pregnancy/ Caesarian section
      • Varicose veins


      • Thrombophilia
      • Hormone replacement therapy/ Oral contraceptive
      • Cardiovascular problems (Congestive cardiac failure, hypertension, congenital heart disease)
      • COPD
      • Obesity

        Symptoms and signs of PE

        In addition, check for signs of DVT (table below).


        The British Thoracic Society recommends to set the clinical probability for each patient who is suspected with a PE. The patient must have

        • Breathlessness/tachypnoea (+/- pleuritic chest pain and +/- haemoptysis) AND
        • Two other factors:
        1. Absence of another clinical explanation
        2. Presence of a major risk factor


        If 1. and 2. true = Clinical probability is high

        If 1. or 2. true=Clinical probabilty is intermediate

        If 1. and 2. false= Clinical probability is low



        Blood test

         Infarction causes:

        • Polymorphonuclear leucocytosis
        • Raised erythrocyte sedimentation rate (ESR)
        • Increased lactate dehydrogenase

        Arterial Blood Gases

        • Normal in healthy individuals
        • Hyperventilation - Hypoxia, hypercapnia
        • Increased A-a gradient

        Check for thrombophilia screen before commencing anticoagulant treatment.


        Chest X-Ray

        Often normal, but can cause:

        • Linear atelectasis
        • Loss of costrophrenic angle (pleural effusion) in 40% of patients
        • Raised hemidiaphragm
        • Focal infiltrates
        • Segmental collapse
        • Wedge-shaped infarct
        • Opaque linear scars (from previous infarcts )



        Usually normal with sinus tachycardia. Other features can occur.

        • Atrial fibrillation/ other types of tachyarrhythmia
        • Right bundle branch block
        • Anterior(V1-V4) T-wave inversion (Right ventricular strain)
        • Classical S1Q3T3 pattern (S wave in lead I, Q wave in lead 3 , inverted T wave in lead 3)- rare 


        Plasma D-dimer

        • Only perform it after assessing clinical probability
        • If clinical probability is high, d-dimer test should not be done.
        • If clinical probability is low and d-dimer is negative, exclude PE.


        Computed tomographic pulmonary angiography (CTPA)

        • Gold standard
        • High sensitivity (>95%)
        • Can show clots up to 5th order (branching) pulmonary arteries
        • Perform within an hour of initial event of massive PE, and within 24 hours of small/medium PE
        • Risk of nephropathy (in diabetics and renal patients) and fluid overload (in patients with heart failure). If so, a leg ultrasound and/or isotope lung scanning might be safer as a first line investigation.
        • Patients with negative CTPA to not require further treatment for PE.


        Isotope lung scan/ Ventilation Perfusion (V/Q) scan

        • Used as first line treatment when a good quality CXR is normal and no significant symptoms of cardiopulmonary disease is present.
        • Also used when patient is pregnant and has no underlying chest disease.
        • When there is no diagnostic result, do further imaging.
        • If the scan is normal, PE is excluded
        • If the scan shows low probability scan and the patient has low or intermediate clinical probability, PE is excluded.
        • If the scan shows high probability and the patient has a high clinical probability, PE is diagnosed.
        • May show areas of pulmonary infarction


          Ultrasound scan

          • Used to detect clots in veins (leg, pelvic)
          • For confirmation but not excluding PE where patients shows signs of DVT. 



            • In massive PE, it may shows dilation of right ventricle, clot in the right ventricular outflow track, and a vigorously contracting left ventricle .


            Transthoracic ultrasound

            • Not widely used
            • Used as an adjuct to identify perfipheral wedge-shaped opacities especially in patients with pleuritic pain.



            PE is an emergency which needs to be treated urgently.

              • Thrombolysis- In massive PE that cause a circulatory collapse. 50mg bolus of alteplase is given.
              • Thrombolectomy- If patient is haemodynamically very severe, perform surgical embolectomy. Catheter is placed through femoral vein to right heart and clots are mechanically removed. Some centres do surgical embolectomy
              • Give low molecular weight heparin(LMWH) and warfarin until INR >2. Continue warfarin for 3-6months. Target INR 2~3(3.5 if recurrent).



              • Low molecular weight heparin prophylaxis SC(eg dalteparin 2500u/24h)   
              • Avoid oral contraceptive pill    
              • Antithromboembolic (TED) compression stockings  
              • Inferior vena cava(IVC) filter via femoral vein for prevention of recurrent PEs . Give anticoagulation with it. Indications:(a) Patients with absolute contraindication with anticoagulationpatients who had a massive PE, (b)Recurrent VTE despite anticoagulation and (c) Post-pulmonary thromboendarterectomy
              • Do risk analysis especially for patients who are more prone to PE (Patients with MI, malignancy, fractures, pneumonia, immobility, etc)
              • Investigate for thrombophilia if patient has recurrent VTE or has a family history of VTE


              British Thoracic Society Standards of Care Committee Pulmonary Embolism Guideline Development Group (2003) 'British Thoracic Society guidelines for the management of suspected acute pulmonary embolism', Thorax, (58), pp. 470-484.

              Longmore M., Wilkinson I.B., Davidson E.H., Foulkes A., Mafi A.R. (2010) Oxford Handbook of Clinical Medicine, 8th edn., Oxford: Oxford University Press.

              Chapman S., Robinson G., Stradling J., West S. (2009) Oxford Handbook of Respiratory Medicine, 2nd edn., Oxford: Oxford University Press.

              Kumar P., Clark M. (2009) Kumar and Clark's Clinical Medicine, 7th edn., : Saunders Elsevier

              British Thoracic Society Standards of Care Committee Pulmonary Embolism Guideline Development Group (January 2010) 'Venous thromboembolism: reducing the risk', National Institute for Health and Clinical Excellence, (92)

              Le Gal G, Righini M, Roy PM, et al. Prediction of pulmonary embolism in the emergency department: the revised Geneva score. Ann Intern Med. 2006;144:165-171.


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