A 34-year-old woman is brought to the emergency department for severe, progressive mid-abd… — USMLE Step 2 CK

A 34-year-old woman is brought to the emergency department for severe, progressive mid-abdominal pain and bilious emesis over the past 24 hours. She has not passed flatus or stool since the pain began. Her medical history includes Crohn disease, which necessitated a terminal ileal resection 7 years ago due to fibrotic strictures. She also has a history of mild asthma and a peripartum cardiomyopathy 3 years ago that has since completely resolved. Current medications include adalimumab. Her temperature is 38.9°C (102.0°F), blood pressure is 88/54 mm Hg, and pulse is 126/min. On physical examination, the abdomen is markedly distended and tympanic. There is severe, diffuse abdominal tenderness with involuntary guarding and rebound tenderness. Bowel sounds are absent.

Laboratory studies show:

Laboratory Test	Result
Leukocyte count	19,500/mm³
Serum sodium	138 mEq/L
Serum potassium	3.9 mEq/L
Serum chloride	102 mEq/L
Serum bicarbonate	14 mEq/L
Lactic acid	4.8 mmol/L

Arterial blood gas analysis on room air:

Test	Result
pH	7.28
PaCO2	28 mm Hg
PaO2	92 mm Hg

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

A
Placement of a nasogastric tube and serial abdominal examinations
B
Computed tomography scan of the abdomen and pelvis
C
Intravenous administration of sodium bicarbonate
Urgent surgical explorationAnswer
E
Administration of intravenous furosemide

Answer

The most appropriate next step is urgent surgical exploration due to signs of a strangulated small bowel obstruction.

The correct answer is urgent surgical exploration. This patient presents with the classic triad of a small bowel obstruction (SBO): colicky abdominal pain, bilious vomiting, and obstipation, likely due to adhesions from her prior surgery or a new Crohn disease stricture. Crucially, she exhibits signs of a strangulated obstruction, including peritonitis (involuntary guarding, rebound tenderness), hemodynamic instability (hypotension, tachycardia), systemic inflammatory response (fever, marked leukocytosis), and bowel ischemia (lactic acidosis causing a high anion gap metabolic acidosis). In any patient with an acute surgical abdomen and hemodynamic instability, emergent laparotomy is the definitive and life-saving next step.

Step-by-Step Solution

Assess the patient's hemodynamic status and physical examination findings.

The patient is hypotensive and tachycardic with fever, and has diffuse abdominal rigidity and rebound tenderness indicating peritonitis.

To determine if the patient has an acute surgical abdomen requiring immediate operative intervention rather than conservative management.

Evaluate the laboratory results and calculate the anion gap and expected respiratory compensation.

The anion gap is elevated at 22 (

138 - (102 + 14)

), driven by lactic acidosis (4.8 mmol/L). Using Winter's formula (

PaCO_2 = 1.5 \times 14 + 8 = 29 \pm 2

), the patient's

PaCO_2

of 28 mm Hg indicates a perfectly compensated metabolic acidosis with no primary respiratory disorder.

To identify the presence of bowel ischemia (lactic acidosis) and to rule out any concurrent primary respiratory failure that might mandate primary airway management over immediate surgery.

Synthesize the history of Crohn disease and prior abdominal surgery with current findings.

The clinical picture confirms a strangulated small bowel obstruction (SBO) likely secondary to adhesions or stricture.

To select the definitive management pathway, which dictates that strangulated SBO in an unstable patient bypasses advanced imaging directly for surgical exploration.

Key Concept

Patients with small bowel obstruction presenting with signs of ischemia or strangulation (peritonitis, fever, lactic acidosis, hemodynamic instability) require immediate surgical exploration.

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic