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Difficulty: Very hardCardiothoracic and Vascular Surgery

A vascular surgery team is evaluating a 74-year-old man on his second day of recovery following an open repair of a 6.8 cm infrarenal abdominal aortic aneurysm. During the procedure, the inferior mesenteric artery was ligated to allow for adequate exposure and graft placement. Today, the patient abruptly develops severe left-sided abdominal pain accompanied by the passage of dark, bloody stool. Current vital signs include a temperature of 38.6°C (101.5°F), blood pressure of 94/58 mmHg, heart rate of 118/min, and respiratory rate of 22/min. Abdominal examination demonstrates exquisite tenderness over the left lower quadrant, accompanied by muscle rigidity, involuntary guarding, and rebound tenderness. Laboratory analysis reveals a leukocyte count of 19,200/mm³ and a serum lactate concentration of 4.5 mmol/L (Normal: 0.5-2.2 mmol/L). Based on these clinical findings, which of the following is the most appropriate next step in management?

  1. A
    Computed tomography angiography of the abdomen and pelvis
  2. Emergent exploratory laparotomyAnswer
  3. C
    Flexible sigmoidoscopy with minimal air insufflation
  4. D
    Initiation of intravenous broad-spectrum antibiotics and bowel rest
  5. E
    Stool assay for Clostridioides difficile toxin and oral vancomycin

Answer

Emergent exploratory laparotomy is required due to signs of transmural colonic necrosis.
The correct approach is an emergent exploratory laparotomy. This patient is presenting with acute colonic ischemia (ischemic colitis), a well-known complication of open abdominal aortic aneurysm (AAA) repair resulting from the ligation of the inferior mesenteric artery (IMA). The left colon relies on collateral circulation from the superior mesenteric artery (via the marginal artery of Drummond) and the internal iliac arteries; if these collaterals are inadequate, ischemia ensues. The presence of left lower quadrant pain and bloody diarrhea post-AAA repair strongly suggests this diagnosis. Crucially, the presence of peritoneal signs (muscle rigidity, involuntary guarding, rebound tenderness) combined with systemic toxicity (high fever, tachycardia, marked leukocytosis, and elevated serum lactate) indicates that the ischemia has progressed to transmural bowel necrosis. When transmural infarction is suspected, conservative management and diagnostic imaging or endoscopy are contraindicated. The patient must be taken immediately to the operating room for an exploratory laparotomy, which typically involves resection of the necrotic bowel and creation of a proximal colostomy.

Step-by-Step Solution

1
Analyze the patient's postoperative timeline and surgical history.
The patient had an open AAA repair with inferior mesenteric artery (IMA) ligation 2 days ago.
IMA ligation disrupts the primary blood supply to the descending and sigmoid colon, establishing a high risk for ischemic colitis if collateral circulation from the superior mesenteric artery is insufficient.
2
Evaluate the presenting symptoms and physical examination findings.
The patient developed sudden left lower quadrant pain, bloody diarrhea, and clear peritoneal signs (guarding, rebound tenderness).
These physical findings differentiate mild mucosal ischemia (pain and bleeding without peritonitis) from severe transmural necrosis (frank peritonitis).
3
Interpret the laboratory results.
Marked leukocytosis (19,200/mm³) and elevated lactate (4.5 mmol/L) are present.
Elevated serum lactate in the setting of acute abdominal pain and peritonitis is a classic metabolic marker for dead or dying bowel (transmural infarction).
4
Determine the most appropriate management based on the clinical severity.
Select emergent exploratory laparotomy.
Transmural bowel necrosis is a surgical emergency. Imaging or endoscopy is contraindicated because they delay life-saving care and increase the risk of bowel perforation.

Key Concept

Diagnosis and management of acute colonic ischemia (ischemic colitis) following abdominal aortic aneurysm repair, specifically recognizing indications for emergent surgery.
Estimated Time:1m 30s
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Topics

Cardiothoracic and Vascular Surgery

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