A 48-year-old woman arrives at the emergency department reporting sudden-onset pleuritic c… — USMLE Step 2 CK

A $48$ -year-old woman arrives at the emergency department reporting sudden-onset pleuritic chest pain and breathlessness that began two hours ago. She has a history of type 2 diabetes mellitus and chronic kidney disease. She underwent a hysterectomy for uterine fibroids three weeks ago. Her temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure is $130/85$ mm Hg, pulse is $118$ /min, and respirations are $26$ /min. Pulse oximetry shows $91\%$ on room air. Examination demonstrates a swollen, tender left calf. Lungs are clear to auscultation bilaterally. Cardiac examination reveals a regular tachycardia but no murmurs or gallops.

Laboratory results are as follows:

Laboratory Test	Result	Reference Range
Serum creatinine	$2.8$ mg/dL	$0.6 - 1.1$ mg/dL
Arterial Blood Gas (Room Air)
pH	$7.50$	$7.35 - 7.45$
PaCO $_2$	$28$ mm Hg	$35 - 45$ mm Hg
PaO $_2$	$62$ mm Hg	$75 - 105$ mm Hg
HCO $_3^-$	$22$ mEq/L	$22 - 28$ mEq/L

Which of the following is the most appropriate next step in the management of this patient?

A
Order a pelvic ultrasound and obtain blood cultures to evaluate for a postoperative source
B
Administer intravenous furosemide and initiate noninvasive positive pressure ventilation
Perform a ventilation-perfusion lung scanAnswer
D
Calculate the Winter formula to determine the adequacy of respiratory compensation
E
Initiate empiric broad-spectrum antimicrobial therapy for healthcare-associated pneumonia

Answer

Perform a ventilation-perfusion lung scan

The patient's clinical presentation of sudden-onset pleuritic chest pain, dyspnea, tachycardia, and a swollen, tender calf three weeks after a major abdominal surgery is highly suspicious for an acute pulmonary embolism (PE). According to the Wells criteria, she has a high pretest probability for a PE. The preferred initial diagnostic imaging modality for patients with suspected PE is computed tomography pulmonary angiography (CTPA). However, CTPA utilizes intravenous iodinated contrast, which carries a significant risk of contrast-induced nephropathy and is generally contraindicated in patients with severe chronic kidney disease (such as this patient with a serum creatinine of 2.8 mg/dL). In patients with a high clinical suspicion of PE who have contraindications to CTPA and a normal chest radiograph (supported by clear lungs on auscultation), a ventilation-perfusion (V/Q) lung scan is the most appropriate next step to safely establish the diagnosis.

Step-by-Step Solution

Evaluate the patient's clinical presentation and establish a pretest probability for pulmonary embolism.

The patient has sudden-onset pleuritic chest pain, dyspnea, tachycardia, a recent surgery, and a unilaterally swollen leg, which indicates a high pretest probability (Wells score) for an acute pulmonary embolism.

Establishing the pretest probability guides the requirement and urgency of objective diagnostic imaging.

Identify any patient-specific contraindications to standard diagnostic imaging protocols.

The patient has a severely elevated serum creatinine of 2.8 mg/dL, indicating advanced chronic kidney disease.

The standard diagnostic test, computed tomography pulmonary angiography (CTPA), requires iodinated contrast, which carries a high risk of contrast-induced nephropathy in patients with poor renal function.

Select the most appropriate alternative diagnostic modality based on the clinical constraints.

A ventilation-perfusion (V/Q) lung scan is selected.

V/Q scanning does not utilize nephrotoxic intravenous contrast and is the preferred initial imaging choice for diagnosing a pulmonary embolism in patients with severe renal impairment and a normal chest radiograph.

Key Concept

Diagnosis of pulmonary embolism in patients with a high pretest probability but absolute contraindications to CT pulmonary angiography (e.g., severe chronic kidney disease) requires alternative objective imaging, most commonly a ventilation-perfusion (V/Q) lung scan.

Estimated Time:1m 30s

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