How do you manage a patient suspected of having a pulmonary embolism?

Ruling Out Pulmonary Embolism: A Practical Approach

To rule out PE, you need the absence of all three key clinical features: tachypnea (>20/min), pleuritic chest pain, and arterial hypoxemia—if all three are absent, PE can be excluded. 1

Clinical Assessment and Risk Stratification

Record the respiratory rate in every patient with suspected PE, as this is a critical discriminating feature that is often overlooked. 1 The presence of unexplained acute dyspnea, hypoxemia, and a normal chest radiograph should trigger immediate investigation for PE. 1

Key Risk Factors to Identify

Predisposing factors are present in 80-90% of PE cases. 1 The most common include:

• Recent immobilization >1 week 1
• Previous DVT or PE 1
• Recent major surgery 1
• Lower limb fractures or surgery 1
• Active malignancy 1
• Pregnancy or postpartum state 1

Important caveat: Young women whose only risk factor is oral contraception who present with isolated pleuritic chest pain are very unlikely to have PE if respiratory rate is <20/min and chest radiograph is normal. 1

Initial Diagnostic Workup

Perform these tests immediately in all patients with suspected PE:

• Chest radiography 1
• ECG 1
• Arterial blood gas measurements 1
• Respiratory rate documentation 1

D-Dimer Testing

Normal D-dimer levels exclude PE in patients with low to intermediate clinical probability. 1, 2 However, the laboratory must offer a reliable D-dimer assay for this exclusion strategy to be valid. 1

Imaging Strategy

CT Pulmonary Angiography (CTPA)

Proceed to CTPA for patients with high clinical probability or elevated D-dimer. 2 This should be performed within 24 hours of clinical suspicion. 1

Critical pitfall: If CTPA reports single subsegmental PE, consider false-positive findings and discuss with radiology for a second opinion before committing to anticoagulation. 2 Subsegmental emboli are often missed and their clinical significance remains debated. 1

Lung Scanning Considerations

Isotope lung scanning is not recommended if: 1

• Unavailable on-site
• Patient has chronic cardiac or respiratory disease
• Chest radiograph is abnormal

When lung scanning is performed, ventilation should be assessed by technetium-labeled aerosol rather than 133Xe. 1 Requests must be accompanied by an estimate of clinical probability. 1

Interpreting Scan Results:

• Normal scan = no PE 1
• Scan + clinical probability both low = no PE 1
• Scan + clinical probability both high = PE present 1
• Any other combination = needs CTPA 1

Alternative: Leg Vein Imaging

Leg ultrasound is an alternative to lung imaging in patients with clinical DVT. 1 This should be the first-line investigation for suspected PE in patients with previous PE, clinical DVT, or chronic cardiorespiratory disease. 1

When PE Cannot Be Excluded

For patients with indeterminate results, further imaging is required rather than management based on clinical features alone. 1 In high clinical probability cases with negative CTPA, valid alternatives include: 1

• Concluding PE has been excluded and stopping heparin
• Considering further imaging for VTE (leg ultrasound, conventional pulmonary angiography)
• Seeking specialist advice

Pulmonary angiography should be considered when other investigations fail to confirm the diagnosis. 1

Immediate Anticoagulation Decision

Start anticoagulation immediately when PE is suspected based on clinical probability, even before diagnostic confirmation is complete, unless active bleeding or absolute contraindications exist. 2 Heparin should be initiated on the basis of high or intermediate clinical suspicion before the diagnosis is clarified. 1

Heparin Dosing

Weight-adjusted heparin: Initial bolus of 80 IU/kg IV, followed by continuous infusion of 18 IU/kg/hour, targeting aPTT 1.5-2.5 times control (45-75 seconds). 2, 1 3

Monitor aPTT: 1

• 4-6 hours after initial bolus
• 6-10 hours after any dose change
• Daily once in therapeutic range