An 8-day-old male infant is brought to the emergency department via ambulance after severa… — USMLE Step 2 CK

An $8$ -day-old male infant is brought to the emergency department via ambulance after several episodes of dark green vomiting. The mother reports that the infant has been increasingly lethargic over the past $12$ hours and has not produced a wet diaper since yesterday. Vital signs include a temperature of $35.4^\circ \text{C}$ ( $95.7^\circ \text{F}$ ), heart rate of $195$ /min, respiratory rate of $65$ /min, and blood pressure of $52/28$ mm Hg. Physical examination reveals an ill-appearing, mottled infant. The abdomen is markedly distended and exquisitely tender to palpation, demonstrating involuntary guarding. A localized area of cutaneous erythema and edema is noted extending across the right hemiabdomen. The skin over the trunk shows scattered blanching erythematous macules with central yellow papules, which the mother states have been present since hospital discharge. Capillary refill is $5$ seconds. Arterial blood gas analysis on room air shows a pH of $7.20$ , $\text{pCO}_2$ of $20$ mm Hg, and $\text{HCO}_3^-$ of $8$ mEq/L. Which of the following is the most appropriate next step in the management of this patient?

Emergent exploratory laparotomyAnswer
B
Upper gastrointestinal series with water-soluble contrast
C
Nasogastric decompression, intravenous antibiotics, and serial abdominal examinations
D
Cerebrospinal fluid analysis and initiation of intravenous acyclovir
E
Endotracheal intubation for assumed hypercapnic respiratory failure

Answer

Emergent exploratory laparotomy

The correct action is emergent exploratory laparotomy. This neonate presents with classic signs of malrotation complicated by midgut volvulus: bilious emesis, severe lethargy, and shock. Crucially, the physical examination reveals a rigid abdomen with localized cutaneous erythema. In a neonate, erythema and edema of the abdominal wall in the setting of obstruction are ominous signs of transmural bowel necrosis and peritonitis. When a patient with a suspected surgical abdomen is hemodynamically unstable or exhibits signs of peritonitis, diagnostic imaging is bypassed. Following concurrent aggressive fluid resuscitation, the patient must be taken immediately to the operating room for exploratory laparotomy to resect necrotic bowel and restore perfusion.

Step-by-Step Solution

Identify the primary pathology from the clinical presentation.

The combination of a neonate with bilious emesis, lethargy, and shock is highly suggestive of malrotation with midgut volvulus.

Bilious emesis in a neonate represents a surgical emergency (distal to the ampulla of Vater obstruction) until proven otherwise.

Evaluate for complications requiring immediate intervention.

The patient exhibits hypothermia, severe hypotension, involuntary guarding, and abdominal wall erythema.

Abdominal wall erythema and rigidity in the setting of obstruction indicate transmural bowel necrosis and impending or actual perforation (peritonitis).

Differentiate significant findings from benign distractors.

The rash (erythematous macules with central yellow papules) is identified as erythema toxicum neonatorum. The acid-base status is evaluated using Winter's formula:

\text{Expected pCO}_2 = (1.5 \times 8) + 8 = 20 \pm 2

Recognizing ETN prevents unnecessary infectious workups. Confirming appropriate respiratory compensation prevents inappropriate respiratory interventions for the severe metabolic acidosis.

Determine the definitive next step in management.

Select emergent exploratory laparotomy.

Although imaging (upper GI series) is diagnostic for malrotation, hemodynamic instability and peritonitis mandate bypassing imaging and proceeding directly to the operating room for surgical exploration and resection of necrotic bowel.

Key Concept

In a neonate with suspected midgut volvulus, the presence of hemodynamic instability or peritonitis (e.g., rigid abdomen, abdominal wall erythema) mandates immediate exploratory laparotomy, superseding standard diagnostic imaging like an upper gastrointestinal series.

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