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Difficulty: MediumDiagnostic Workup and Test Sequencing

Emergency medical services transport a primigravid patient at 26 weeks gestation to the acute care bay following the sudden onset of right-sided pleuritic chest discomfort and shortness of breath. She has no significant past medical history, and her pregnancy has been uncomplicated to date. Vital signs show a heart rate of 115/min, respiratory rate of 24/min, blood pressure of 110/70 mmHg, and oxygen saturation of 93% on room air. Physical examination reveals clear lung fields bilaterally and a normal cardiac rhythm without murmurs. Her right leg is mildly edematous compared to the left, although she denies localized calf pain. An electrocardiogram demonstrates sinus tachycardia, and a portable chest radiograph is unremarkable. Which of the following is the most appropriate next step in the diagnostic evaluation of this patient?

  1. Bilateral lower extremity compression ultrasonographyAnswer
  2. B
    Computed tomography pulmonary angiography
  3. C
    Plasma D-dimer assay
  4. D
    Ventilation-perfusion (V/Q) scan
  5. E
    Transthoracic echocardiography

Answer

Bilateral lower extremity compression ultrasonography
The most appropriate next step in the diagnostic evaluation of a pregnant patient with suspected pulmonary embolism and signs of deep vein thrombosis (such as unilateral leg edema) is bilateral lower extremity compression ultrasonography. The diagnostic algorithm in pregnancy prioritizes minimizing radiation exposure to the fetus. Since the treatment for deep vein thrombosis and pulmonary embolism is identical (therapeutic anticoagulation), finding a clot in the lower extremity secures the diagnosis of venous thromboembolism and eliminates the need for radiating chest imaging. Only if the compression ultrasound is negative should the clinician proceed to a ventilation-perfusion scan or computed tomography pulmonary angiography.

Step-by-Step Solution

1
Analyze the patient's clinical presentation.
The patient is a pregnant female presenting with acute pleuritic chest pain, dyspnea, tachycardia, hypoxia, and unilateral leg edema.
These findings strongly suggest a venous thromboembolism (VTE), specifically a pulmonary embolism originating from a deep vein thrombosis.
2
Determine the constraints of the patient's current physiological state.
The patient is pregnant, which means diagnostic modalities utilizing ionizing radiation should be avoided or deferred if alternative imaging can secure the diagnosis.
Radiation exposure poses teratogenic and oncogenic risks to the developing fetus, and maternal breast tissue is also highly radiosensitive during pregnancy.
3
Select the appropriate diagnostic sequence for suspected pulmonary embolism in pregnancy.
Bilateral lower extremity compression ultrasonography is chosen as the initial test.
Because the patient exhibits a sign of deep vein thrombosis (unilateral leg edema), identifying a clot via a non-invasive, radiation-free ultrasound establishes the diagnosis of VTE and immediately allows for the initiation of anticoagulation, bypassing the need for chest imaging entirely.

Key Concept

In pregnant patients with suspected pulmonary embolism, particularly those with signs of deep vein thrombosis, bilateral lower extremity compression ultrasonography is the preferred initial diagnostic test to secure the diagnosis without fetal radiation exposure.
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Topics

Diagnostic Workup and Test Sequencing

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