A 3-year-old boy is brought to the pediatric emergency department due to sudden onset of s… — USMLE Step 2 CK

A $3$ -year-old boy is brought to the pediatric emergency department due to sudden onset of severe, colicky abdominal pain that began $12$ hours ago. Initially, the pain was intermittent, but it has now become constant. He has vomited bilious material four times in the past $6$ hours. The parents report that over the last month, the child had two episodes of painless, dark red rectal bleeding, which resolved spontaneously. On physical examination, the child appears lethargic and toxic. Temperature is $39.1^\circ\text{C}$ ( $102.4^\circ\text{F}$ ), pulse is $160/\text{min}$ , respirations are $32/\text{min}$ , and blood pressure is $75/40\text{ mmHg}$ . Abdominal examination reveals a rigid, distended abdomen with diffuse guarding, rebound tenderness, and a palpable sausage-shaped mass in the right mid-abdomen. Laboratory studies show:

Test	Result
Leukocyte count	$22,000/\text{mm}^3$
Serum lactate	$5.2\text{ mmol/L}$
Serum bicarbonate	$12\text{ mEq/L}$
Arterial pH	$7.25$
Arterial pCO $_2$	$26\text{ mmHg}$

Following initial fluid resuscitation, which of the following is the most appropriate next step in management?

Immediate exploratory laparotomyAnswer
B
Air contrast enema reduction
C
Technetium-99m pertechnetate scintigraphy
D
Intravenous administration of broad-spectrum antibiotics and close observation
E
Intravenous sodium bicarbonate infusion

Answer

Immediate exploratory laparotomy

The correct answer is immediate exploratory laparotomy. This patient presents with classic signs of intussusception (colicky abdominal pain, bilious emesis, sausage-shaped mass) complicated by bowel ischemia and peritonitis (lethargy, fever, hypotension, abdominal rigidity, and lactic acidosis). Furthermore, his history of painless lower gastrointestinal bleeding suggests an underlying Meckel diverticulum acting as a pathological lead point. While an air or water contrast enema is the standard initial therapy for uncomplicated intussusception, it is absolutely contraindicated in the presence of peritonitis, free air, or profound hemodynamic instability due to the high risk of bowel perforation. In such critically ill patients, immediate surgical intervention (exploratory laparotomy) is required to reduce the intussusceptum, resect any necrotic bowel, and remove the lead point.

Step-by-Step Solution

Analyze the patient's acute presentation and physical examination findings.

The child has a palpable sausage-shaped mass, colicky pain, and bilious vomiting, which are classic for intussusception. However, he also exhibits fever, hypotension, and a rigid abdomen, indicating peritonitis and bowel ischemia.

Identifying complications is critical to determining whether medical or surgical management is indicated.

Evaluate the historical clue of painless rectal bleeding.

Previous episodes of painless lower gastrointestinal bleeding in a toddler strongly suggest a Meckel diverticulum, which is likely acting as a pathological lead point for the current intussusception.

Intussusception in children older than 2 years often involves a pathological lead point that requires surgical resection.

Assess the laboratory values and acid-base status.

The elevated lactate confirms tissue ischemia. The arterial blood gas shows a metabolic acidosis (pH 7.25, HCO3 12 mEq/L) with perfect respiratory compensation (Expected pCO2 = 1.5 * 12 + 8 = 26 mmHg).

Accurate acid-base interpretation prevents inappropriate medical interventions (like bicarbonate) and underscores the need for source control.

Determine the next best step in management based on patient stability.

While uncomplicated intussusception is managed with non-operative enema reduction, the presence of peritonitis and hemodynamic instability necessitates immediate exploratory laparotomy.

Enema reduction under pressure in an ischemic bowel will cause frank perforation.

Key Concept

Management of complicated pediatric intussusception

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