#31 – Small Bowel Obstruction




Small bowel obstruction (SBO) is one of the more common surgical emergencies in US, due to the increased intraluminal pressures which can lead to intestinal ischemia and risk of spontaneous rupture.  Overall mortality increases significantly if either of these occur.  It is estimated that over 300,000 surgeries per year occur in the US for bowel obstructions, with the small bowel making up around 80%.  Although it can happen at age, there is a higher trend to older patients and thee is equal incidence with both genders.

Risk Factors

The most common cause of SBO is postoperative adhesions, but there are numerous other causes that you should keep on your differential.

Signs and Symptoms

  • Abdominal pain
    • Paroxysms of periumbilical pain (3-5 minutes)
  • Nausea
  • Vomiting
  • Obstipation

Physical Examination

  • Dehydration
    • Tachycardia, orthostasis, decreased urine output
  • +/- Distension
  • Changes in bowel sounds
    • Hyperactive à muffled à absent
  • Percussion changes
    • Tympanic with distension
    • Dullness with fluid
  • Peritoneal signs if perforation present
  • +/- hemoccult

Laboratory Studies

  • CBC with differential
    • Anemia can point to a chronic condition
  • BMP
  • ABG
    • Acidosis = bowel ischemia, volume depletion
    • Alkalosis = vomiting
  • Serum lactate

Imaging Studies

  • Plain Radiographs
    • Dilated loops of small bowel with air/fluid levels on upright film
    • May also see a paucity of gas in distal intestines
    • Small bowel dilation ≥ 2.5cm is diagnostic

  • Abdominal CT
    • Much more sensitive and can also identify the specific causes
    • Can also identify a transition point
    • Other radiological signs on CT consistent with SBO include:
      • Bowel wall thickening > 3mm
      • Submucosal edema
      • Mesenteric edema
      • Ascites
      • Target sign (intussusception)
      • Whirl sign (volvulus)
      • Venous cut-off sign (thrombosis)
  • Ultrasound
    • Not as good as CT, but better than plain radiography
  • Special Considerations on Radiography
    • Closed-Loop Obstruction
      • High risk for ischemia, perforation, and ischemic bowel
    • Ischemia and Perforation


  • Initial
    • NPO
    • Fluid resuscitation
    • Surgery consultation
    • Gastrointestinal decompression
      • Not in EVERY patient, but good for patients with significant distension, nausea, and/or vomiting
    • Surgery
      • Nonspecific signs of bowel ischemia:
        • Fever
        • Leukocytosis
        • Tachycardia
        • Continuous and/or worsening abdominal pain
        • Metabolic acidosis
        • Peritonitis
      • High likelihood of bowel resection if ≥ 3 of the following:
        • Pain > 4 days
        • Abdominal guarding on exam
        • Elevated CRP > 75 mg/dL
        • Leukocytosis > 10,000
        • > 500cc fluid of intraabdominal fluid
        • Reduced wall contrast enhancement on CT
    • Observation
      • If no high-risk surgical signs present, observation with serial examinations may be used for 12-24 hours in patients with:
        • Early postoperative obstruction
        • Inflammatory bowel disease
        • Gallstone ileus
        • Infectious small bowel disease
        • Colonic diverticular disease
      • Exploration should proceed if no improvement


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