How to rule out pulmonary embolism (PE) in a pregnant patient with normal vitals?

Diagnostic Algorithm for Pulmonary Embolism in Pregnant Patients with Normal Vitals

For pregnant patients with suspected pulmonary embolism (PE) and normal vital signs, a structured diagnostic approach starting with bilateral compression ultrasound of the lower extremities is recommended when signs or symptoms of deep vein thrombosis (DVT) are present.

Initial Assessment

• Despite normal vital signs, PE remains a leading cause of pregnancy-related mortality in developed countries, accounting for 20% of maternal deaths in the United States 1
• Common presenting symptoms in pregnant women with confirmed PE include:
  • Dyspnea (62%)
  • Pleuritic chest pain (55%)
  • Cough (24%)
  • Sweating (18%) 1
• Normal vital signs do not exclude PE in pregnancy, as physiologic changes of pregnancy may mask typical signs 1

Diagnostic Algorithm

Step 1: Evaluate for DVT Symptoms

• If signs or symptoms of DVT are present:
  • Perform bilateral compression ultrasound (CUS) of lower extremities 1
  • If CUS is positive: Begin anticoagulation treatment without further imaging 1
  • If CUS is negative: Proceed to chest imaging 1

Step 2: D-dimer Testing

• D-dimer testing is not recommended to exclude PE in pregnancy 1
• Studies show D-dimer has poor sensitivity (73%) and very low specificity (15%) for PE in pregnancy 1, 2
• False negative D-dimer results have been documented in pregnant women with confirmed PE 1

Step 3: Chest Radiograph

• Perform chest radiograph (CXR) as the first radiation-associated procedure 1
• CXR helps determine the next appropriate imaging test 1

Step 4: Advanced Imaging Based on CXR Results

• If CXR is normal:
  • Perform lung scintigraphy (V/Q scan) as the next imaging test 1
  • V/Q scans have a high diagnostic yield (75-94%) in pregnant women 1
• If CXR is abnormal:
  • Perform CT pulmonary angiography (CTPA) 1
• If V/Q scan is nondiagnostic:
  • Proceed to CTPA rather than digital subtraction angiography 1

Radiation Considerations

• Fetal radiation doses from properly performed diagnostic tests present no measurably increased risk of prenatal death, malformation, or impairment of mental development 1
• When performing V/Q scans in pregnant women:
  • Reduce administered dose of radiopharmaceuticals by a factor of 2 or more 1
  • If perfusion scan is performed first and is normal, ventilation scan can be avoided 1

Special Considerations

• Magnetic resonance pulmonary angiography (MRPA) is not recommended due to:
  • Lack of validation studies in pregnancy 1
  • Concerns about gadolinium effects on the fetus 1
• Digital subtraction angiography is rarely needed and should be reserved for cases where catheter-directed therapy is being considered 1

Common Pitfalls to Avoid

• Do not rely on normal vital signs to exclude PE in pregnant patients 1
• Do not use D-dimer to rule out PE in pregnancy due to high false-negative rates 1, 2
• Do not proceed directly to CTPA without first performing CXR in pregnant patients with normal vital signs 1
• Do not overlook signs and symptoms of DVT, as a positive lower extremity ultrasound can establish the need for treatment without exposing the fetus to radiation 1