A 23-year-old man with sickle cell disease (HbSS) arrives at the emergency department acco… — USMLE Step 2 CK

A 23-year-old man with sickle cell disease (HbSS) arrives at the emergency department accompanied by his roommate, reporting severe chest pain, a productive cough, and rapidly worsening shortness of breath over the past day. He was evaluated two days prior for a mild vaso-occlusive crisis and discharged with oral analgesics. Vital signs show a temperature of $39.2^\circ\text{C}$ ( $102.6^\circ\text{F}$ ), blood pressure of $110/70\text{ mmHg}$ , pulse of $122/\text{min}$ , and respiratory rate of $28/\text{min}$ . Pulse oximetry reveals an oxygen saturation of $85\%$ on room air. Examination shows scleral icterus and decreased breath sounds with dullness to percussion over the left lower lung field.

Laboratory studies reveal:

Laboratory Test	Result
Hemoglobin	$6.8\text{ g/dL}$ (Baseline: $9.2\text{ g/dL}$ )
Leukocyte count	$18,500/\text{mm}^3$
Platelet count	$190,000/\text{mm}^3$
Reticulocyte count	$14\%$

A chest radiograph demonstrates a new, dense left lower lobe consolidation. Immediate interventions including intravenous fluids, supplemental oxygen, and pain management are initiated.

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

A
Administer a simple packed red blood cell transfusion and observe closely
B
Administer intravenous furosemide and initiate noninvasive positive pressure ventilation
C
Withhold broad-spectrum antibiotics pending the results of sputum culture and sensitivity
Perform an automated red blood cell exchange transfusionAnswer
E
Obtain an arterial blood gas to calculate the expected respiratory compensation for metabolic acidosis

Answer

Perform an automated red blood cell exchange transfusion.

The correct answer is to perform an automated red blood cell exchange transfusion. Acute chest syndrome is a life-threatening complication of sickle cell disease defined by a new radiodense pulmonary infiltrate accompanied by fever, respiratory distress, or chest pain. The primary pathophysiology involves vaso-occlusion in the pulmonary microvasculature. Management depends on severity. This patient exhibits severe features, specifically a rapidly dropping hemoglobin and severe hypoxemia (oxygen saturation of 85% on room air). In such severe cases, exchange transfusion is urgently indicated to rapidly remove sickled erythrocytes, lower the hemoglobin S percentage, and improve oxygen delivery without causing hyperviscosity. Simple transfusions are reserved for milder cases without severe hypoxemia.

Step-by-Step Solution

Identify the primary diagnosis based on the clinical presentation and diagnostic findings.

The patient has a fever, new pulmonary infiltrate, chest pain, and severe hypoxemia in the setting of sickle cell disease, which establishes the diagnosis of acute chest syndrome (ACS).

Recognizing ACS is critical because it is a leading cause of mortality in sickle cell patients and requires specific, rapid intervention.

Assess the severity of the acute chest syndrome to determine the appropriate transfusion strategy.

The patient has severe hypoxemia (oxygen saturation of 85% on room air) and a rapidly declining hemoglobin level.

Severity dictates the intervention; severe disease requires more aggressive red blood cell replacement (exchange) than mild disease (simple transfusion).

Determine the definitive treatment indicated for severe acute chest syndrome.

Automated red blood cell exchange transfusion is selected as the next step.

Exchange transfusion rapidly decreases the percentage of hemoglobin S and improves oxygenation without precipitating dangerous hyperviscosity, which is necessary when severe features are present.

Key Concept

Severe acute chest syndrome in sickle cell disease, characterized by marked hypoxemia or rapidly progressive respiratory failure, requires emergent automated red blood cell exchange transfusion.

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