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Difficulty: MediumOrdering Imaging Studies

A 68-year-old man presents to the emergency department complaining of sudden-onset shortness of breath and right-sided pleuritic chest pain that began 2 hours ago. He underwent a right total hip arthroplasty 10 days ago. His medical history includes type 2 diabetes mellitus and hypertension. Temperature is 37.1°C (98.8°F), blood pressure is 138/86 mmHg, pulse is 112/min, and respirations are 24/min. Oxygen saturation is 91% on room air. Physical examination reveals clear lungs bilaterally and a normal cardiovascular examination. His right thigh is slightly swollen consistent with recent surgery, but there is no calf tenderness or erythema. Laboratory results show a serum creatinine level of 2.6 mg/dL (baseline 1.2 mg/dL). A bedside chest radiograph is unremarkable. Which of the following is the most appropriate next imaging study to establish the diagnosis?

  1. Ventilation-perfusion lung scanAnswer
  2. B
    Computed tomography pulmonary angiography
  3. C
    Lower extremity compression ultrasonography
  4. D
    Magnetic resonance angiography of the chest
  5. E
    Fluoroscopic pulmonary angiography

Answer

Ventilation-perfusion lung scan
This patient presents with a high clinical probability of a pulmonary embolism (PE) given his recent orthopedic surgery, tachycardia, acute dyspnea, and pleuritic chest pain. The standard initial diagnostic imaging test for a PE is computed tomography pulmonary angiography (CTPA). However, this patient presents with an acute kidney injury (AKI), as evidenced by a significantly elevated serum creatinine. The iodinated contrast required for CTPA is nephrotoxic and contraindicated in AKI. In a patient with a normal bedside chest radiograph and a contraindication to CTPA, a ventilation-perfusion (V/Q) lung scan is the most appropriate, definitive diagnostic imaging study.

Step-by-Step Solution

1
Determine the patient's pretest probability for a pulmonary embolism.
The patient has a high clinical probability based on recent major orthopedic surgery, tachycardia, dyspnea, and pleuritic pain.
Establishing a high pretest probability dictates that definitive diagnostic imaging should be ordered immediately, rather than starting with a screening D-dimer test.
2
Identify patient-specific contraindications to standard imaging modalities.
The patient has an acute kidney injury (creatinine 2.6 mg/dL), which is a contraindication to iodinated contrast.
Computed tomography pulmonary angiography (CTPA) requires iodinated contrast, which risks severe contrast-induced nephropathy in this setting.
3
Select the most appropriate alternative imaging study given the patient's baseline workup.
A ventilation-perfusion (V/Q) lung scan should be ordered.
A V/Q scan is highly sensitive and specific for pulmonary embolism when the patient has a normal chest radiograph, making it the ideal alternative to CTPA in patients with renal failure.

Key Concept

In patients with a high clinical suspicion for pulmonary embolism and a strict contraindication to iodinated contrast (such as acute kidney injury), a ventilation-perfusion (V/Q) lung scan is the imaging modality of choice, provided the baseline chest radiograph is normal.
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Ordering Imaging Studies

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