Pulmonary embolism

Overview

•Dyspnoea - sudden onset, most common symptom; V/Q mismatch + reflex hyperventilation
•Pleuritic chest pain - sharp, worse on inspiration; peripheral emboli causing pulmonary infarction
•Tachycardia - most reliable sign; >90% of cases
•Tachypnoea - ~95% of cases
•Hypoxia - with clear chest on auscultation (ventilated but not perfused)
•Low-grade fever - underappreciated; can mimic pneumonia
•Hypotension/syncope - massive PE; obstructive shock
•Signs of DVT - unilateral calf swelling, erythema, tenderness; ~30% of cases
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Classic ABG in PE: ↓pO2 + ↓pCO2 + ↑pH = type 1 respiratory failure with respiratory alkalosis (hyperventilation). Classic exam picture: post-surgery or COCP patient, sudden dyspnoea + pleuritic pain, clear chest, sinus tachycardia on ECG, normal CXR.

Investigations

•Calculate two-level PE Wells score first - determines whether to proceed to imaging or D-dimer
•Wells >4 (PE likely): arrange immediate imaging
•Wells ≤4 (PE unlikely): D-dimer first - negative excludes PE; positive → proceed to imaging
•Chest X-ray - required before CTPA or V/Q to exclude other diagnoses (pneumothorax, pneumonia); classically normal in PE
•CTPA - gold standard; first-line imaging when Wells >4 and renal function adequate
•V/Q scan - preferred over CTPA if creatinine clearance <30 mL/min (contrast nephrotoxicity), pregnancy, or contrast allergy
•ECG - sinus tachycardia most common (44%); right bundle branch block (18%); right axis deviation (16%); S1Q3T3 classically quoted but rarely seen, not sensitive or specific
•Proximal leg vein ultrasound - consider if CTPA negative but DVT still suspected
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D-dimer is highly sensitive but not specific. In post-operative patients, active cancer, sepsis, or pregnancy, a positive D-dimer adds almost no value - go straight to imaging if Wells >4.
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Sinus tachycardia is the most common ECG finding in PE. S1Q3T3 is classically quoted but rarely seen in practice.

Management

Haemodynamically UNSTABLE (hypotensive - massive PE)
Thrombolysis with alteplase (recombinant tPA) - first-line. If thrombolysis contraindicated → surgical embolectomy (last resort). If alteplase given during CPR → continue CPR for 60-90 minutes to allow drug effect.
Haemodynamically STABLE
First-line: apixaban (DOAC) - start immediately if imaging delayed (Wells >4). Rivaroxaban is an alternative DOAC. If DOAC unsuitable (severe renal impairment, antiphospholipid syndrome): LMWH then warfarin or LMWH then dabigatran/edoxaban.
Duration of anticoagulation
  1. 1Provoked PE (surgery, immobility, pregnancy, COCP within 3 months): 3 months
  2. 2Unprovoked PE (no identifiable trigger): 6 months
  3. 3Cancer-associated PE: minimum 6 months
  4. 4Recurrent VTE / persistent risk: consider lifelong anticoagulation
Outpatient vs inpatient
  1. 1Use PESI score to determine if low-risk patient can be managed as outpatient
IVC filter
  1. 1Reserved for patients where anticoagulation is absolutely contraindicated or fails to prevent recurrent PE; 5% recurrence risk even with filter in situ
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Thrombolysis indication: hypotension (systolic BP <90 mmHg or drop ≥40 mmHg for >15 min) = haemodynamic instability = massive PE. Hypoxia alone, RV strain on ECG alone, or extensive DVT alone do NOT meet the threshold.
•Absolute contraindications to thrombolysis: prior intracranial haemorrhage or structural intracranial disease; ischaemic stroke within 3 months; active internal bleeding; recent brain/spinal surgery or significant head trauma; bleeding diathesis (haemophilia, antiphospholipid syndrome with bleeding)

Complications

•Pulmonary infarction - peripheral emboli; pleuritic pain, haemoptysis, exudative pleural effusion (PE is a key cause of exudative effusion, not transudate)
•Obstructive shock / cardiac arrest - acute right heart failure from massive PE
•Chronic thromboembolic pulmonary hypertension (CTEPH) - failure of clot resolution → fixed pulmonary hypertension months-years later
•Recurrent VTE - higher risk after unprovoked PE and in persistent risk states (cancer, thrombophilia)