A 72-year-old woman is evaluated in the hospital for sudden-onset shortness of breath and … — USMLE Step 2 CK

A $72$ -year-old woman is evaluated in the hospital for sudden-onset shortness of breath and right-sided pleuritic chest pain. She was admitted $3$ days ago for an elective left total hip arthroplasty. Her past medical history is significant for ischemic cardiomyopathy (baseline left ventricular ejection fraction $45\%$ ), mild chronic obstructive pulmonary disease, and a pituitary macroadenoma treated with transsphenoidal resection $5$ years ago resulting in panhypopituitarism. Her current medications include aspirin, lisinopril, metoprolol succinate, tiotropium, hydrocortisone, and levothyroxine.

Temperature is $37.6^\circ C$ ( $99.7^\circ F$ ), pulse is $118/min$ , blood pressure is $132/84$ mm Hg, and respirations are $26/min$ . Pulse oximetry shows $88\%$ on room air. Physical examination reveals clear lungs to auscultation bilaterally. The jugular venous pressure is $9$ cm $H_2O$ . The right calf is swollen, erythematous, and tender to palpation.

Laboratory results are as follows:
Leukocyte count: $9,500/mm^3$
Thyroid-stimulating hormone (TSH): $1.1 \mu U/mL$ (Normal: $0.4-4.0 \mu U/mL$ )
Free thyroxine (T4): $0.6 ng/dL$ (Normal: $0.9-1.7 ng/dL$ )

Arterial blood gas on room air:
pH: $7.50$
$PaCO_2$ : $28$ mm Hg
$PaO_2$ : $56$ mm Hg
$HCO_3^-$ : $22 mEq/L$

An electrocardiogram shows sinus tachycardia with a prominent S wave in lead I, a Q wave in lead III, and an inverted T wave in lead III.

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

Computed tomography angiography of the chestAnswer
B
Administration of intravenous furosemide
C
Initiation of empiric vancomycin and piperacillin-tazobactam
D
Evaluation of expected PaCO2 compensation using Winter's formula
E
Increase in levothyroxine dosage for primary hypothyroidism

Answer

Computed tomography angiography of the chest

The correct answer is computed tomography angiography of the chest because this patient presents with classic signs of an acute pulmonary embolism (PE). Her presentation includes sudden-onset dyspnea, pleuritic chest pain, tachycardia, hypoxia, and evidence of a deep vein thrombosis (DVT) in the setting of recent major orthopedic surgery (total hip arthroplasty). Her arterial blood gas demonstrates acute respiratory alkalosis secondary to hyperventilation, and the electrocardiogram shows the S1Q3T3 pattern, which reflects acute right ventricular strain. For hemodynamically stable patients with a high clinical probability of PE, the definitive diagnostic imaging modality is CT pulmonary angiography.

Step-by-Step Solution

Analyze the patient's clinical presentation and risk factors.

The patient has sudden-onset dyspnea, pleuritic chest pain, hypoxia, and unilateral calf swelling

3

days after major orthopedic surgery.

This combination is highly suspicious for a deep vein thrombosis (DVT) that has embolized, causing an acute pulmonary embolism (PE).

Interpret the diagnostic data provided in the stem.

The ABG reveals a primary respiratory alkalosis (pH

7.50

, low

PaCO_2

) driven by tachypnea. The ECG demonstrates the classic S1Q3T3 pattern.

Respiratory alkalosis and the S1Q3T3 pattern (indicating acute right ventricular strain) further support the diagnosis of acute PE.

Determine the next best step in management.

Computed tomography (CT) angiography of the chest is the most appropriate next step.

In a hemodynamically stable patient with a high pretest probability for PE (elevated Wells score), CT pulmonary angiography is the definitive diagnostic imaging modality before initiating long-term anticoagulation.

Key Concept

The diagnosis of pulmonary embolism in a hemodynamically stable patient with high clinical suspicion relies on computed tomography (CT) pulmonary angiography.

Estimated Time:1m 30s

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