Pulmonary Embolism (PE)

• Pulmonary embolism (PE) is a blood clot (thrombus) in the pulmonary arteries.
• An embolus is a thrombus that has traveled in the blood, often from a deep vein thrombosis (DVT) in a leg.
• The thrombus blocks blood flow to lung tissue and strains the right side of the heart.
• DVTs and PEs are collectively known as venous thromboembolism (VTE).

Risk Factors

• Immobility, recent surgery, long-haul travel, pregnancy, and hormone therapy with oestrogen increase the risk of DVT or PE.
• Malignancy, polycythaemia (raised haemoglobin), systemic lupus erythematosus, and thrombophilia are also risk factors.
• Prophylactic treatment is used in many situations (e.g., surgery) to reduce the risk of VTE.

VTE Prophylaxis

• Every patient admitted to hospital is assessed for their risk of venous thromboembolism (VTE).
• Higher-risk patients receive prophylaxis with low molecular weight heparin (e.g., enoxaparin) unless contraindicated.
• Contraindications include active bleeding or existing anticoagulation with warfarin or a DOAC.
• Anti-embolic compression stockings are also used unless contraindicated (e.g., peripheral arterial disease).

Presentation

• Pulmonary embolism can be asymptomatic or cause sudden death.
• Presenting features include shortness of breath, cough, haemoptysis (coughing up blood), and pleuritic chest pain.
• Other symptoms are hypoxia, tachycardia, raised respiratory rate, low-grade fever, and haemodynamic instability causing hypotension.
• Signs and symptoms of a DVT, such as unilateral leg swelling and tenderness, may be present.

PERC Rule

• The pulmonary embolism rule-out criteria (PERC) are used when the clinician estimates less than a 15% probability of a pulmonary embolism.
• If all PERC 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 when PE is suspected.
• It accounts for risk factors (e.g., recent surgery) and clinical findings (e.g., heart rate above 100 and haemoptysis).

Diagnosis

• A chest x-ray is usually normal in a pulmonary embolism but is required to rule out other pathology.
• If the Wells score indicates PE is likely, perform a CT pulmonary angiogram (CTPA) or alternative imaging.
• If the Wells score indicates PE is unlikely, perform a d-dimer test; if positive, perform a CTPA.
• D-dimer is a sensitive (95%) but not a specific blood test for VTE.
• D-dimer helps exclude VTE where there is a low suspicion and is almost always raised if there is a DVT.
• Conditions that can cause a raised d-dimer outside of PE include pneumonia, malignancy, heart failure, surgery, and pregnancy.

Imaging Options

• A CT pulmonary angiogram is the first-line imaging to diagnose PE.
• Ventilation-perfusion single photon emission computed tomography (V/Q SPECT) scan is the second option.
• Planar ventilation–perfusion (VQ) scan is a third option.

CT Pulmonary Angiogram (CTPA)

• CTPA consists of a chest CT scan with intravenous contrast that highlights the pulmonary arteries to demonstrate any blood clots.
• CTPA is the first-line imaging for pulmonary embolism because it is readily available and provides a more definitive assessment.
• It also gives information about alternative diagnoses, such as pneumonia or malignancy.

Ventilation-Perfusion (VQ) Scan

• VQ scan involves using radioactive isotopes and a gamma camera to compare ventilation with the perfusion of the lungs.
• VQ scans are used in patients with renal impairment, contrast allergy or risk from radiation, where a CTPA is unsuitable.
• Isotopes are inhaled to fill the lungs, and a picture is taken to demonstrate ventilation.
• Next, a contrast containing isotopes is injected, and a picture is taken to illustrate perfusion.
• A pulmonary embolism will show a deficit in perfusion, as the thrombus blocks blood flow to the lung tissue, but the lung tissue will still be ventilated.
• Planar V/Q scans produce 2D images where V/Q SPECT scans produce 3D images, making them more accurate.

Management

• Supportive management includes hospital admission (if required), oxygen, analgesia (if required), and monitoring for any deterioration.
• Anticoagulation is the mainstay of management.
• Treatment-dose apixaban or rivaroxaban is recommended as first-line.
• Low molecular weight heparin (LMWH) is the main alternative and should be started immediately if 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 is injecting a fibrinolytic medication that rapidly dissolves clots but carries a significant risk of bleeding.
• Thrombolytic agents are streptokinase, alteplase, and tenecteplase.

Thrombolysis Delivery

• Intravenously using a peripheral cannula is one method.
• Catheter-directed thrombolysis into the pulmonary arteries using a central catheter is the other method.

Long-Term Anticoagulation

• Treatment options are a DOAC, warfarin, or LMWH.
• Direct-acting oral anticoagulants (DOACs) do not require monitoring, and options are apixaban, rivaroxaban, edoxaban, and dabigatran.
• Exceptions for DOACs include severe renal impairment (creatinine clearance less than 15 ml/min), antiphospholipid syndrome and pregnancy.
• Warfarin is a vitamin K antagonist with a target INR between 2 and 3 when treating DVTs and PEs, and is first-line in patients with antiphospholipid syndrome.
• Low molecular weight heparin (LMWH) is the first-line anticoagulant in pregnancy.

Duration of Anticoagulation

• Three months with a reversible cause, then review.
• Beyond 3 months with unprovoked PE, recurrent VTE, or an irreversible underlying cause
• Three to six months in active cancer, then review.