How to manage a pregnant woman with sudden onset dyspnea (shortness of breath), oxygen saturation of 96% on room air, and a non-diagnostic Ventilation/Perfusion (V/Q) scan?

Management of Pregnant Woman with Sudden Onset Shortness of Breath and Non-Diagnostic V/Q Scan

For pregnant women with suspected pulmonary embolism (PE) and a non-diagnostic V/Q scan, anticoagulant therapy should be initiated while awaiting further diagnostic results if clinical suspicion is high and bleeding risk is low. 1, 2

Initial Assessment

• Evaluate vital signs immediately, with particular attention to:

  • Oxygen saturation (currently 96% on room air)
  • Heart rate (tachycardia >100 bpm suggests PE)
  • Blood pressure (hypotension may indicate massive PE)
  • Respiratory rate (tachypnea is common in PE)

• Check for risk factors for PE:

  • Prior history of venous thromboembolism
  • Immobility
  • Thrombophilia
  • Family history of thrombosis
  • Obesity
  • Advanced maternal age

Diagnostic Algorithm After Non-Diagnostic V/Q Scan

1. Obtain chest X-ray if not already done (strong recommendation) 1

   • This should be the first radiation-associated procedure

2. Perform bedside echocardiography to assess for right ventricular dysfunction 2

   • If positive for acute RV dysfunction in a hemodynamically unstable patient, consider immediate reperfusion therapy without further testing

3. Consider CT pulmonary angiography (CTPA) as the next step after a non-diagnostic V/Q scan 1, 2

   • CTPA is preferred over digital subtraction angiography (strong recommendation) 3
   • Optimize CTPA protocol for pregnancy:
     • Use automated bolus triggering
     • High iodine flux (flow rate 4.5-6 ml/s)
     • High iodine concentration (350-400 mg I/ml)
     • Clear breathing instructions to minimize Valsalva effects 1

4. Consider bilateral lower limb compression ultrasonography as a radiation-free alternative 4

   • A positive finding of proximal deep vein thrombosis confirms PE diagnosis

Treatment Approach

• Initiate therapeutic anticoagulation if clinical suspicion remains high while awaiting definitive diagnosis 1, 2

  • Low molecular weight heparin is the preferred agent in pregnancy
  • Continue until PE is definitively ruled out

• For hemodynamically stable patients with non-diagnostic V/Q scan:

  • Complete the diagnostic algorithm with CTPA
  • If CTPA is also non-diagnostic, clinical judgment based on pretest probability should guide treatment decisions

• For hemodynamically unstable patients:

  • Consider thrombolysis if massive PE is confirmed
  • Multidisciplinary approach involving maternal-fetal medicine specialists, cardiologists, and emergency physicians 2

Important Considerations

• Radiation exposure concerns:

  • V/Q scan: Maternal breast radiation 0.98-1.07 mGy; Lung tissue 5.7-13.5 mGy
  • CTPA: Maternal breast radiation 10-60 mGy; Lung tissue 39.5 mGy 2
  • Both tests have fetal radiation doses well below accepted thresholds

• When performing imaging studies:

  • Keep radiation dose as low as reasonably achievable
  • For CTPA: adjust technical factors for maternal size, limit scan length
  • For V/Q scan: use half the usual administered activity of Tc-99m macroaggregated albumin and increase scan time 1

• Clinical follow-up data suggests that withholding anticoagulation in pregnant women with normal or non-diagnostic V/Q scans who have low clinical probability may be safe 5

• The 2018 American Society of Hematology guidelines suggest V/Q lung scanning over CTPA for initial evaluation, but acknowledge that CTPA is appropriate when V/Q results are non-diagnostic 1

The key pitfall to avoid is delaying treatment in a patient with high clinical suspicion of PE. While diagnostic accuracy is important, the risk of untreated PE in pregnancy (potential maternal and fetal mortality) outweighs the risk of unnecessary anticoagulation in most cases.