A 65-year-old man with a 15-year history of structuring Crohn's disease, chronic obstructi… — USMLE Step 2 CK

A $65$ -year-old man with a $15$ -year history of structuring Crohn's disease, chronic obstructive pulmonary disease (COPD), and heart failure with preserved ejection fraction is currently hospitalized. He was admitted two days ago with colicky abdominal pain, obstipation, and bilious vomiting due to a mechanical small bowel obstruction. Initial management included bowel rest, intravenous fluids, and nasogastric decompression.

Over the past four hours, the patient reports a sudden transition from intermittent colicky pain to severe, unremitting diffuse abdominal pain. His temperature is $39.2^\circ\text{C}$ ( $102.6^\circ\text{F}$ ), blood pressure is $88/54\text{ mm Hg}$ , heart rate is $128/\text{min}$ , and respiratory rate is $28/\text{min}$ . Physical examination reveals a rigid, silent abdomen with exquisite diffuse rebound tenderness and involuntary guarding.

Blood cultures drawn upon admission are currently growing *Escherichia coli* that is susceptible to ceftriaxone, ciprofloxacin, and metronidazole, but resistant to ampicillin.

Laboratory Study	Result
Leukocyte count	$18,500/\text{mm}^3$ (with $15\%$ bands)
Arterial pH	$7.27$
pCO $_2$	$29\text{ mm Hg}$
pO $_2$	$70\text{ mm Hg}$
HCO $_3^-$	$13\text{ mEq/L}$

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

Emergent exploratory laparotomy and initiation of intravenous ceftriaxone and metronidazoleAnswer
B
Continue nasogastric decompression and initiate high-dose intravenous hydrocortisone
C
Emergent exploratory laparotomy and initiation of intravenous meropenem and vancomycin
D
Intravenous sodium bicarbonate infusion followed by surgical consultation
E
Noninvasive positive pressure ventilation and intravenous furosemide

Answer

The most appropriate next step is emergent exploratory laparotomy combined with targeted antimicrobial therapy using intravenous ceftriaxone and metronidazole.

The correct course of action involves emergent exploratory laparotomy and targeted intravenous antibiotics. The patient's clinical picture has acutely worsened to include peritonitis (rigid abdomen, rebound tenderness) and hemodynamic instability. These are classic signs that a mechanical small bowel obstruction has progressed to bowel strangulation, ischemia, or perforation. Uncomplicated small bowel obstruction is managed conservatively, but strangulation is an absolute indication for immediate surgery. Furthermore, since blood cultures have already identified an *Escherichia coli* strain susceptible to ceftriaxone, and intra-abdominal infections are typically polymicrobial involving anaerobes, the combination of ceftriaxone and metronidazole provides optimal, targeted antimicrobial stewardship without unnecessarily utilizing ultra-broad-spectrum agents.

Step-by-Step Solution

Analyze the change in the patient's clinical presentation.

The transition from intermittent colicky pain to severe unremitting pain, along with new-onset fever, hypotension, tachycardia, and a rigid abdomen, strongly indicates bowel strangulation or perforation.

Recognizing the progression from uncomplicated small bowel obstruction to complicated obstruction (ischemia/infarction) is critical, as it changes the management from conservative to operative.

Evaluate the patient's acid-base status using Winter's formula.

Expected pCO2 = (1.5 × 13) + 8 = 27.5 ± 2 (range: 25.5 to 29.5). The measured pCO2 of 29 mm Hg falls within this range, indicating a fully compensated metabolic acidosis.

This confirms that the respiratory response is appropriate for the metabolic (lactic) acidosis secondary to bowel ischemia, meaning primary buffering interventions like sodium bicarbonate are not indicated.

Determine the appropriate antimicrobial regimen based on culture results and stewardship principles.

Targeted therapy with ceftriaxone plus metronidazole is selected.

Blood cultures identify an organism susceptible to ceftriaxone, allowing for targeted treatment. De-escalating from broader agents (like meropenem) prevents resistance, while adding metronidazole ensures necessary anaerobic coverage for a gastrointestinal source.

Formulate the definitive next step in management.

Immediate surgical intervention with appropriate targeted antibiotics.

Definitive source control via exploratory laparotomy is life-saving for strangulated bowel.

Key Concept

Patients with a small bowel obstruction who develop peritoneal signs (rigidity, rebound tenderness), fever, and hemodynamic instability must undergo immediate surgical exploration for suspected strangulation, alongside targeted antimicrobial therapy based on available culture susceptibilities.

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