Pulmonary embolism (PE)

Overview

Pulmonary embolism (PE) is a medical emergency caused by obstruction of pulmonary arterial blood flow, usually by thrombotic material originating from the deep venous system.

PE is a major manifestation of venous thromboembolism (VTE), which includes:

• Deep vein thrombosis (DVT).

• Pulmonary embolism (PE).

Approximately 90% of clinically significant PE originates from proximal DVT involving the popliteal, femoral, or iliac veins.

PE causes:

• Ventilation–perfusion mismatch.

• Hypoxaemia.

• Increased pulmonary vascular resistance.

• Right ventricular strain.

• Possible cardiovascular collapse.

Severity ranges from incidental/asymptomatic PE to massive PE with haemodynamic instability.

Risk factors

Risk factors are related to Virchow’s triad.

Venous stasis

• Prolonged immobilization.

• Bed rest.

• Long-haul travel.

• Recent surgery, especially orthopaedic surgery.

• Stroke with paralysis.

• Heart failure.

Endothelial injury

• Major trauma.

• Surgery.

• Central venous catheters.

Hypercoagulability

• Malignancy.

• Pregnancy and postpartum state.

• Oral contraceptives or hormone therapy.

• Inherited thrombophilia:

  • Factor V Leiden.

  • Protein C deficiency.

  • Protein S deficiency.

• Antiphospholipid syndrome.

• Obesity.

• Smoking.

Previous VTE is the strongest predictor of recurrence.

Clinical presentation

Presentation depends on clot size and cardiopulmonary reserve.

Common features include:

• Transient dyspnoea and tachypnoea without other clinical features.

• Sudden onset dyspnoea.

• Pleuritic chest pain.

• Cough.

• Haemoptysis.

• Pleural effusion.

• Pulmonary infiltrates.

• Tachycardia.

• Arrhythmia.

Severe presentations include:

• Severe dyspnoea and tachypnoea.

• Right-sided heart failure.

• Cardiovascular collapse.

• Hypotension.

• Syncope.

• Coma.

Other non-specific presentations:

• Resistant cardiac failure.

• Wheezing.

• Fever.

• Apprehension.

• Confusion.

Classification of PE severity

Massive PE

• Sustained hypotension.

• Shock.

• Haemodynamic collapse.

Submassive PE

• Right ventricular dysfunction without hypotension.

Low-risk PE

• Haemodynamically stable.

• No evidence of right ventricular strain.

Investigations

Diagnosis requires clinical assessment and objective confirmation.

Laboratory investigations

• D-dimer.

• PT.

• INR.

• aPTT.

• Full blood count.

• Renal function tests.

• Arterial blood gases where indicated.

• Cardiac biomarkers in suspected right ventricular strain.

Imaging

• CT pulmonary angiography (CTPA):

  • Gold standard imaging test.

Other investigations:

• Chest X-ray.

• Compression ultrasonography of lower limbs.

• Ventilation–perfusion scan if CTPA is contraindicated.

• Echocardiography for right ventricular dysfunction.

Management

PE is a medical emergency.

Management aims to:

• Prevent clot extension.

• Prevent recurrence.

• Prevent complications.

Non-pharmacological management

• Oxygen therapy for hypoxia.

• Haemodynamic support.

• Cautious IV fluids where required.

• Vasopressors if hypotensive.

• Intensive care monitoring in massive PE.

Inferior vena cava (IVC) filter may be considered if:

• Anticoagulation is contraindicated.

Pharmacological treatment

Treat as Deep Vein Thrombosis (DVT) section.

Long-term anticoagulation is required to prevent:

• Recurrent VTE.

• Thrombus extension.

Warfarin-based regimen

• Warfarin PO 5 mg 24 hourly.

AND

• Initial unfractionated heparin or low molecular weight heparin therapy overlapping for 5 days.

Continue warfarin according to INR monitoring.

Therapeutic INR range:

• 2–3 for VTE.

• 2.5–3.5 for patients with mechanical heart valves.

Monitoring:

• Monitor INR after 5–7 days of treatment.

• Continue monitoring as needed throughout treatment duration.

Low molecular weight heparin regimen

• Low molecular weight heparin SC 1 mg/kg 24 hourly.

Alternative regimen:

• Enoxaparin SC 1 mg/kg 12 hourly.

Unfractionated heparin regimen

• Unfractionated heparin IV 75 units/kg loading dose.

AND

• Continuous infusion 18 units/kg/hour.

Monitoring:

• Monitor aPTT before and during treatment.

Rivaroxaban regimen

• Rivaroxaban PO 15 mg 12 hourly for 21 days.

THEN

• Rivaroxaban PO 20 mg 24 hourly for the remaining duration of treatment.

Adolescents and children

Options include:

• Unfractionated heparin loading dose 75 units/kg.

THEN

• 15–25 units/kg/hour by IV infusion.

OR

• 250 units/kg SC 12 hourly.

Pregnant women

Warfarin is teratogenic and should not be used during pregnancy.

Use:

• Low molecular weight heparin SC 1 mg/kg 12 hourly for the whole duration of treatment.

Thrombolysis

Consider in:

• Massive PE with shock.

• Persistent hypotension.

Example:

• Alteplase IV 100 mg over 2 hours.

Duration of treatment

For venous thromboembolism:

• Acquired thromboembolism:

  • Treatment usually lasts 3–6 months.

• Inherited thrombophilia:

  • Lifelong anticoagulation may be required.

Additional guidance:

• Provoked PE: 3–6 months.

• Unprovoked PE: ≥6 months or extended therapy.

• Recurrent VTE: long-term anticoagulation.

Warfarin precautions

Warfarin interacts with many medicines.

Precautions should be taken when administering warfarin with other drugs.

If warfarin overdose or toxicity occurs:

• Stop warfarin.

AND

• Give fresh frozen plasma (FFP) 10–15 ml/kg.

AND

• Give vitamin K IV 5 mg stat.

Restart warfarin after:

• Bleeding has stopped.

• INR is within therapeutic range.

Use a lower dosage when restarting.

VTE prophylaxis in bedridden patients

Options:

• Enoxaparin SC 40 mg once daily.

OR

• Rivaroxaban PO 10 mg once daily.

Continue until ambulation resumes.

Complications

• Recurrent PE.

• Chronic thromboembolic pulmonary hypertension (CTEPH).

• Right heart failure.

• Sudden cardiac death.

Prevention

Primary prevention

• Early mobilization after surgery.

• Mechanical prophylaxis using compression devices.

• Prophylactic LMWH in high-risk hospitalized patients.

Secondary prevention

• Appropriate duration of anticoagulation.

• Risk factor modification:

  • Weight reduction.

  • Smoking cessation.