A 72-year-old man underwent surgical repair of an aneurysm of the infrarenal aorta. He received perioperative prophylaxis with a second-generation cephalosporin antibiotic. On the first postoperative day he complains of progressive abdominal pain and bloody diarrhea. His temperature is 38.5° C (101° F), blood pressure is 110/65 mm Hg, pulse is 110/min and respirations are 22/min. His abdomen is mildly distended and tender to palpation. The tenderness is mostly in the left lower quadrant without rebound. Femoral pulses are full and symmetric. His white blood cell count is 12,000/mm3. Which of the following is the most likely diagnosis?
Bowel ischemia is one known complication (1-7% incidence) of abdominal aortic aneurysm repair. It results from inadequate colonic collateral arterial perfusion to the left and sigmoid colon after loss of the inferior mesenteric artery during aortic graft placement. Patients present with abdominal pain and bloody diarrhea. Fever and leukocytosis may also be present. This adverse effect can be minimized by checking sigmoid colon perfusion following placement of the aortic graft.
(Choice A) C. difficile is the most common cause of nosocomial diarrhea. Pseudomembranous colitis occurs following antibiotic treatment and most commonly causes a voluminous watery diarrhea in addition to abdominal pain and fever. Bloody diarrhea is rare. Also, it is uncommon to develop C. difficile infection so early after the antibiotic use (typically takes 4-5 days).
(Choice B) Invasive diarrhea, such as that caused by E. coli (EIEC) or Shigella, manifests with bloody, purulent diarrhea and tenesmus. These are less likely in this setting.
(Choice C) Aortoenteric fistula is a rare and late complication where the duodenum erodes into the proximal part of the aortic graft.
(Choice E) Iatrogenic bowel perforation may be suspected after any abdominal operation. Signs of peritoneal irritation are usually present. Bloody diarrhea is usually not a feature of perforation.
Educational Objective:
Bowel ischemia and infarction are possible early complications of operation on the abdominal aorta, such as AAA repair.