A pulmonary embolism (PE) is a blocked blood vessel in your lungs, most often due to a blood clot. It is common and can be asymptomatic but can be life-threatening if the clot is large and near the centre of the lung. With a massive PE immediate management is necessary.

Causes

A common cause of PE is deep vein thrombosis (DVT). This is a condition in which a blood clot (thrombosis) forms within a deep vein, commonly in the lower limbs. PE’s can be caused by other blockages in the lungs such as air bubbles, fatty material or other forms of emboli, however, these other causes are very rare. The blood clot from the leg can dislodge and pass up and block an artery in the lung.

Risk factors

Thromboembolic risk factors make PE’s more likely to occur. These include:

• Cancer.
• Trauma or major surgery.
• Hospitalisation or immobilisation.
• Pregnancy, oral contraceptive use or HRT.
• Family history of DVT or PE.
• Blood clotting disorders.
• Smoking.
• Obesity.

However, a PE can take place unprovoked, in the absence of any identifiable risk factors.

Symptoms

• Sudden shortness of breath.
• Chest pain that is often worse on deep inspiration.
• Anxiety.
• Dizziness.
• Tachycardia or palpitations.
• Cough.
• Haemoptysis.

Diagnoiss and investigations

1. A detailed history and full physical exam should be performed.
2. Baseline bloods including clotting, full blood count, renal function and liver function.
3. ECG.
4. CXR.

If clinical suspicion of a PE is low you should use the Pulmonary embolism rule-out criteria (the PERC rule) to determine if further investigations are needed.

If PE is suspected you can use the PE Wells score to review a patients PE risk factors.

1. PE likely (Wells score more than 4 points).

• You should offer a computed tomography pulmonary angiogram (CTPA) and anticoagulation treatment, after discussing with a senior.
• If PE is identified by CTPA you should continue anticoagulation treatment or if anticoagulation treatment is contraindicated, consider a mechanical intervention.

2. PE unlikely (Wells score 4 points or less).

• You should offer a D-dimer test (be aware there are numerous causes of a falsely raised d-dimer).
• If positive a CTPA/VQ and anticoagulation will be the next step but this should be discussed with a senior.
• If negative STOP therapeutic anticoagulation and think about an alternative diagnosis.

Differentials to consider

• Pneumothorax.
• Pneumonia.
• Acute exacerbation of asthma/COPD.
• Acute coronary syndrome.
• Acute congestive heart failure.

Management

It is recommended that anticoagulation is initiated without delay in patients with high-risk PE.

If unstable

• Review for signs of haemodynamic instability (pallor, tachycardia, hypotension, shock, and collapse).
• Keep to an ABCDE structure and escalate to your senior early if you have concerns.
• A bedside transthoracic echocardiogram should be done  to look for right ventricular dysfunction, if present, consider thrombolysis.
• Additionally norepinephrine should be considered in unstable patients with high-risk PE.

Thrombolytic therapy leads to faster improvements in pulmonary obstruction, pulmonary artery pressure, and pulmonary vascular resistance in patients with PE, compared with unfractionated heparin alone.

In normotensive patients with intermediate-risk PE, thrombolytic therapy is associated with a significant reduction in the risk of collapse, but this was paralleled by an increased risk of extracranial and intracranial bleeding.

If stable

Patients that are low risk with confirmed PE can be treated at home and the length of anticoagulation treatment will depend on whether the PE is classified as provoked or unprovoked.

Provoked and unrpovoked pulmonary embolism

Provoked:

• Provoked PE occurs in a patient with a major clinical risk factor (within 3 months of PE).
• These include surgery, trauma, significant immobility, pregnancy, oral contraception or HRT.
• Consider stopping anticoagulation treatment 3 months after a provoked PE if the provoking factor is no longer present.

Unprovoked:

• A PE is categorised as unprovoked when it occurs in a patient with no antecedent major clinical risk factor for VTE discussed above or when a PE occurs in patients with active cancer, thrombophilia or a family history of VTE, because these are underlying risks that remain constant.
• For patients with an unprovoked PE they should have baseline bloods reviewed and a full physical examination.
• They may require further investigations for cancer and should be considered for antiphospholipid antibodies and hereditary thrombophilia investigations.
• For patients with an unprovoked PE, consider continuing anticoagulation beyond 3 months or beyond 6 months for those with active cancer.

Patients should be given advice about the risk of PE recurrence.

Prevention

Continued anticoagulant therapy for secondary prevention is indicated in selected patients. For these patients, the decision to continue should be discussed with the patient and will depend on their risk of venous thromboembolism (VTE) recurrence and their risk of bleeding. You can consider their risk of bleeding with the HAS-BLED score and can consider stopping anticoagulation if the score is 4 or more.

Non-medical ways of preventing a PE:

• Regular exercise.
• Keeping hydrated.
• Stopping smoking.
• Healthy diet and weight.
• Leg exercises after surgery or on long haul flights.

Complications

If a PE is left untreated it can be associated with significant mortality. Complications include recurrent PE’s, pulmonary hypertension, right heart failure, collapse and cardiac arrest. There is also strong evidence that thrombolysis rapidly improves physiological parameters both angiographically and haemodynamically in PE. In 1971, Miller and colleagues demonstrated that thrombolysis significantly reduced pulmonary artery pressure

Useful resources and references

1. National Institute for Health and Clinical Excellence. Clinical Knowledge Summary: Pulmonary Embolism (October 2020). Available at: https://cks.nice.org.uk/topics/pulmonary-embolism/
2. Howard, Luke SGE, et al. “British Thoracic Society Guideline for the initial outpatient management of pulmonary embolism (PE).” Thorax 73.Suppl 2 (2018): ii1-ii29.
3. British Lung Foundation- What can I do to avoid getting a pulmonary embolism? (March 2018)  Available at: https://www.blf.org.uk/sites/default/files/Pulmonary%20embolism%20v4%20downloadable%20PDF.pdf
4. National Institute for Health and Clinical Excellence. Venous thromboembolic diseases: diagnosis, management and thrombophilia testing (26 March 2020) Link- https://www.nice.org.uk/guidance/ng158
5. Tarbox AK, Swaroop M. Pulmonary embolism. Int J Crit Illn Inj Sci. 2013;3(1):69-72. doi:10.4103/2229-5151.109427. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3665123/
6. MedCalc Version 19.8- https://www.mdcalc.com/perc-rule-pulmonary-embolism
7. Jenkins, Peter O., et al. “Should thrombolysis have a greater role in the management of pulmonary embolism?.” Clinical medicine 9.5 (2009): 431. Available at: https://www.rcpjournals.org/content/clinmedicine/9/5/431
8. Konstantinides, Stavros V., et al. “2019 ESC Guidelines for the diagnosis and management of acute pulmonary embolism developed in collaboration with the European Respiratory Society (ERS) The Task Force for the diagnosis and management of acute pulmonary embolism of the European Society of Cardiology (ESC).” European heart journal 41.4 (2020): 543-603. Available at: https://academic.oup.com/eurheartj/article/41/4/543/5556136

Written by: Dr Caitlin Rea (FY2)
Edited by: Mudassar Khan (Y4 Medical Student)