A 2-year-old boy with sickle cell disease (HbSS) is brought to the emergency department by… — USMLE Step 2 CK

A $2$ -year-old boy with sickle cell disease (HbSS) is brought to the emergency department by his parents due to profound weakness and a rapidly enlarging abdomen over the past $6$ hours. He has been unusually sleepy and difficult to arouse. His temperature is $37.0^\circ\text{C}$ ( $98.6^\circ\text{F}$ ), heart rate is $168/\text{min}$ , blood pressure is $70/40\text{ mm Hg}$ , and respiratory rate is $32/\text{min}$ . Physical examination reveals marked conjunctival pallor. His abdomen is distended, firm, and diffusely tender. The spleen edge is palpable $6\text{ cm}$ below the left costal margin, which is a new finding compared to his baseline. Capillary refill time is $4$ seconds. Laboratory studies reveal:

Hemoglobin: $4.2\text{ g/dL}$ (baseline $8.5\text{ g/dL}$ )
Reticulocytes: $14\%$
Platelets: $75,000/\text{mm}^3$
Leukocytes: $12,500/\text{mm}^3$

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

Intravenous isotonic fluid resuscitation and packed red blood cell transfusionAnswer
B
Immediate transport to the radiology suite for a computed tomography scan of the abdomen
C
Administration of broad-spectrum intravenous antibiotics and blood cultures
D
Emergent exploratory laparotomy and splenectomy
E
Observation with serial abdominal examinations and laboratory draws every 4 hours

Answer

The most appropriate next step is immediate intravenous isotonic fluid resuscitation and packed red blood cell transfusion to treat hypovolemic shock.

The correct answer addresses the immediate life-threatening issue: hypovolemic shock secondary to acute splenic sequestration. In this condition, sickled red blood cells obstruct the splenic venous outflow, causing rapid, massive pooling of blood within the spleen. This depletes the systemic circulation of volume and red blood cells, resulting in the classic triad of an acutely enlarging spleen, a sharp drop in hemoglobin (with compensatory reticulocytosis), and hypovolemic shock. The immediate life-saving intervention is rapid administration of intravenous isotonic fluids and packed red blood cell (pRBC) transfusion to restore intravascular volume and prevent cardiovascular collapse.

Step-by-Step Solution

Analyze the patient's clinical presentation and vital signs.

The patient has marked tachycardia (

168/\text{min}

), hypotension (

70/40\text{ mm Hg}

), and prolonged capillary refill, indicating acute hypovolemic shock.

Recognizing shock is the first step in prioritizing emergency management.

Evaluate the physical exam and laboratory findings in the context of sickle cell disease.

The acute drop in hemoglobin, compensatory high reticulocyte count, thrombocytopenia, and newly massive spleen strongly point to acute splenic sequestration crisis.

Differentiating splenic sequestration from other sickle cell emergencies (like aplastic crisis, which would have low reticulocytes) determines the specific pathophysiology.

Determine the most appropriate immediate intervention.

The acute pooling of blood in the spleen has caused severe intravascular volume depletion. This requires immediate restoration of volume and oxygen-carrying capacity.

Medical stabilization with isotonic fluids and packed red blood cells is the life-saving priority before any surgical or diagnostic considerations.

Key Concept

Acute splenic sequestration crisis is a life-threatening complication of sickle cell disease characterized by rapid pooling of blood in the spleen, leading to acute severe anemia, reticulocytosis, thrombocytopenia, rapidly enlarging spleen, and hypovolemic shock. The immediate treatment is intravascular volume expansion and blood transfusion.

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