Pulmonary Embolism in pregnancy

Venous thromboembolism Risk approximately 10x more common vs non pregnant women Affects 1 in 1000 pregnant women Hypercoagulable state begins with conception and returns to normal approximately 8 weeks post partum

What are we worried about? Does the patient have a pulmonary embolism? How is the fetus affected? How is the mother affected?

Fetal/maternal dose Literature is confusing. Confusion likely due to variation in values reported arising from multiple factors, including patient body habits, stage of pregnancy, radionuclide dose, CT parameters or number of detectors, and method of dose calculation.

Fetal/Maternal dose An Official American Thoracic Society/Society of Thoracic Radiology Clinical Practice Guideline: Evaluation of Suspected Pulmonary Embolism In Pregnancy Ann N. Leung, An Official American Thoracic Society/Society of Thoracic Radiology Clinical Practice Guideline: Evaluation of Suspected Pulmonary Embolism In Pregnancy Ann, N. LeungAmerican Thoracic Society Am J Respir Crit Care Med Vol 184. pp 1200–1208, 2011

Maternal risk Estimated radiation dose to the breasts with CTPA is 10- 70 mSv vs V/Q 1.5 mSv. BEIR VII: Lifetime attributable risk of breast cancer from a breast dose of 20 mGy is approx. 1/1200 age 20, 1/200 age 30, and1/3500 age 40. A single 10 mGy dose increases lifetime risk in a 30-35 yo by up to14%. Risk during pregnancy likely increased due to increased glandular tissue.

Fetal risk CDC

Fetal risk

Fetal risk

V/Q Advantage: Low maternal dose. Disadvantage: Intermediate/Non-diagnostic study may require additional imaging. Indeterminate studies are reported to be less common during pregnancy.

CTPA Advantage: Ability to diagnose other pulmonary pathology. Better interobserver agreement Disadvantage: Maternal radiation dose, inadequate bolus or patient motion decreases sensitivity and may require further imaging. Indeterminate study is reported to be more common during pregnancy due to maternal physiologic changes.

Iodinated contrast Maternal risk same as general population, allergic reaction and nephrotoxicity. Fetal risk: Contrast passes to fetus via placenta or from aspirated amniotic fluid. Theoretical risk of fetal thyroid dysfunction. However, no convincing evidence of IV contrast induced thyroid dysfunction and neonatal thyroid screening is routinely performed.

Recommendation in the literature The American Congress of Obstetricians and Gynecologists (ACOG) and the Fleischner Society recommend pulmonary CT angiography. 2/3 of the PIOPED investigators and the American Thoracic Society/Society of Thoracic Radiology ( group included cardio-thoracic radiologists, NM physicians, pulmonologists, and OB/gyns) recommend V/Q.

ACR appropriateness criteria

What should the ER do? 1. D-dimer: Nonspecific but a normal has a negative predictive value of >95%. 2. CXR and Lower Ext Venous USG 3. If LEU is positive, no further imaging may be needed. 4. If LEU is negative, consider CTPA or V/Q.

What do WE do? ALARA: Reduce rad dose for both CT and V/Q CT: Use the pregnancy protocols already in place. This will significantly reduce the breast/lung dose. V/Q: 1/2 or less dose MAA for perfusion and no Ventilation study. If ventilation is performed, xenon only, NO aerosolized DTPA

Recommendation If we exclude cost of exam, time to acquire, and fetal dose (as both studies produce a low dose and literature varies as to which is greater), then we consider maternal radiation dose and diagnostic capabilities of the exams. V/Q: If CXR negative. Significantly reduced maternal dose compared to CTPA is the primary consideration. CTPA: Although maternal dose is higher, it is significantly reduced using pregnancy protocol CT. Ability to diagnose other pathology and high interobserver agreement being primary considerations.

Suspected PE in pregnancy D-Dimer: Normal, >95% negative predictive value. Probably should not be used by itself, but gives confidence with a negative LEU. LEU positive for DVT —> stop. CXR positive, LEU negative—>CTPA CXR negative, LEU negative —> V/Q V/Q indeterminate/nondiagnostic—>CTPA