A 27-year-old man with a 4-year history of ileocolonic Crohn disease presents to the emerg… — USMLE Step 2 CK

A 27-year-old man with a 4-year history of ileocolonic Crohn disease presents to the emergency department with a 2-day history of progressive, colicky abdominal pain, nausea, and bilious vomiting. He reports that his baseline bowel habit is 3 loose stools daily, but he has not passed stool or flatus for the past 24 hours. He admits to being nonadherent to his prescribed infliximab therapy for the last 6 months.

His temperature is 38.3°C (100.9°F), blood pressure is 112/68 mm Hg, pulse is 115/min, and respiratory rate is 22/min. Physical examination shows a distended abdomen with hypoactive bowel sounds. There is significant tenderness in the right lower quadrant with localized involuntary guarding and rebound tenderness.

Laboratory results are as follows:
Leukocyte count: 16,500/mm³
Hemoglobin: 12.1 g/dL
Platelet count: 450,000/mm³
Serum sodium: 136 mEq/L
Serum potassium: 3.2 mEq/L
Serum chloride: 102 mEq/L
Serum bicarbonate: 15 mEq/L
Blood urea nitrogen: 38 mg/dL
Serum creatinine: 1.3 mg/dL

Arterial blood gas (room air):
$pH$ : 7.32
$pCO_2$ : 30 mm Hg
$pO_2$ : 92 mm Hg
Lactate: 4.5 mmol/L (Normal: 0.5-1.5 mmol/L)

An upright abdominal radiograph shows multiple dilated loops of small bowel with air-fluid levels and a paucity of gas in the colon.

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

Emergency exploratory laparotomyAnswer
B
Placement of a nasogastric tube and administration of intravenous fluids
C
Intravenous corticosteroid therapy and bowel rest
D
Computed tomography of the abdomen and pelvis with intravenous contrast
E
Intravenous normal saline and sodium bicarbonate administration

Answer

Emergency exploratory laparotomy

The correct answer is emergency exploratory laparotomy. This patient presents with a small bowel obstruction (SBO), as evidenced by colicky abdominal pain, bilious vomiting, obstipation, and dilated small bowel loops with air-fluid levels on radiography. In a patient with Crohn disease, SBO is often due to fibrostenotic strictures or acute inflammation and is typically managed conservatively with bowel rest, nasogastric decompression, and intravenous corticosteroids if an inflammatory flare is suspected. However, this patient exhibits severe 'red flag' signs of bowel strangulation and ischemia, including fever, tachycardia, localized peritonitis (involuntary guarding and rebound tenderness), marked leukocytosis, and a high anion gap metabolic acidosis secondary to hyperlactatemia (lactate 4.5 mmol/L). When clinical or laboratory signs strongly suggest bowel ischemia or impending perforation, immediate surgical exploration is required. Delaying surgery significantly increases the risk of transmural necrosis, free perforation, sepsis, and mortality.

Step-by-Step Solution

Identify the primary clinical syndrome from the patient's history, physical examination, and radiograph.

The patient has a small bowel obstruction (SBO), indicated by colicky abdominal pain, bilious vomiting, obstipation, and dilated small bowel loops with air-fluid levels on X-ray.

Establishing the primary diagnosis is the necessary first step before determining the severity and underlying etiology.

Evaluate the patient for complications of SBO, specifically clinical signs of bowel strangulation or ischemia.

The patient exhibits 'red flag' signs: fever (38.3°C), tachycardia (115/min), localized peritonitis (involuntary guarding and rebound tenderness), marked leukocytosis (16,500/mm³), and hyperlactatemia (4.5 mmol/L).

Differentiating between simple and complicated (strangulated) SBO dictates whether management should be conservative or surgical.

Analyze the acid-base status to ensure no other acute derangements require immediate stabilization prior to surgery.

The patient has a

pH

of 7.32,

HCO_3^-

of 15 mEq/L, and

pCO_2

of 30 mm Hg. Using Winter's formula (

1.5 \times 15 + 8 = 30.5 \pm 2

), the respiratory compensation is adequate, confirming a simple high anion gap metabolic acidosis due to elevated lactate.

Accurate acid-base interpretation confirms that the acidemia is purely driven by tissue ischemia, reinforcing the need for emergent source control rather than medical correction with bicarbonate.

Determine the definitive next step in management based on the presence of a complicated SBO.

The patient requires an emergency exploratory laparotomy.

While uncomplicated SBO in Crohn disease is often managed medically (with steroids or bowel rest), the presence of bowel ischemia and peritonitis is an absolute indication for immediate surgical intervention to prevent free perforation and death.

Key Concept

Patients with a small bowel obstruction who develop signs of strangulation or ischemia (e.g., fever, tachycardia, localized peritonitis, leukocytosis, lactic acidosis) require immediate emergency exploratory laparotomy, bypassing conservative management or further imaging.

Estimated Time:2m 0s

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