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Small bowel obstruction

Mechanical obstruction


  • Small bowel obstruction accounts for 5% of acute surgical admissions
  • In UK the commonest causes are:
    • Adhesions (60%)
    • Strangulated hernia (20%)
    • Malignancy (5%)
    • Volvulus (5%)


  • Proximal dilatation occurs above obstructing lesion
  • Results in the accumulation of gas and fluid and reduced reabsorption
  • Dilation of the gut wall produced mucosal oedema
  • This impairs venous and then arterial blood flow
  • Intestinal ischaemia eventually results in infarction and perforation of that segment of bowel
  • Ischaemia also results in bacterial and endotoxin translocation
  • The overall effect is progressive dehydration, electrolyte imbalance and systemic toxicity

Clinical feature

  • Colicky central abdominal pain
  • Vomiting - early in high obstruction
  • Abdominal distension - extent depends on level of obstruction
  • Absolute constipation - late feature of small bowel obstruction
  • Dehydration associated with tachycardia, hypotension and oliguria
  • Features of peritonism indicate strangulation or perforation


  • Supine abdominal X-ray shows dilated small bowel
  • May be normal if no air fluid interfaces
  • Valvulae coniventes differentiate small from large intestine
  • Erect abdominal film rarely provided additional information

small bowel obstruction


  • Adequate resuscitation prior to surgery is vital
  • May require more than 5 litres of intravenous crystalloid
  • Adequacy of resuscitation should be judged by urine output or central venous pressure
  • Surgery in under resuscitated patient is associated with increased mortality
  • If obstruction presumed to be due to adhesions and there are no features of peritonism
    • Conservative management for up to 48 hours is often safe
    • Requires regular clinical review
  • If features of peritonism or systemic toxicity present
    • Need to consider early operation
    • Exact procedure will depend on underlying cause

Indications for surgery

  • Absolute
    • Generalised peritonitis
    • Localised peritonitis
    • Visceral perforation
    • Irreducible hernia
  • Relative
    • Palpable mass lesion
    • 'Virgin' abdomen
    • Failure to improve
  • Trial of conservatism
    • Incomplete obstruction
    • Previous surgery
    • Advanced malignancy
    • Diagnostic doubt - possible ileus

Paralytic ileus

  • Functional obstruction most commonly seen after abdominal surgery
  • Also associated with trauma, intestinal ischaemia, sepsis
  • Small bowel is distended throughout its length
  • Absorption of fluid, electrolytes and nutrients is impaired
  • Significant amounts of fluid may be lost from the extracellular compartment

Clinical features

  • Usually history of recent operation or trauma
  • Abdominal distension is often apparent
  • Pain is often not a prominent feature
  • If no nasogastric tube in-situ vomiting may occur
  • Large volume aspirates my occur via nasogastric tube
  • Flatus will not be passed until resolution of the ileus
  • Auscultation will reveal absence of bowel sounds


  • Plain abdominal x-ray may show dilated loops of small bowel
  • Gas may be present in the colon
  • If doubt as to whether there is a mechanical or functional obstruction
  • Water soluble contrast study may be helpful


  • Prevention is better than cure
  • Bowel should be handled as little as possible
  • Fluid and electrolyte derangements should be corrected
  • Sources of sepsis should be eradicated
  • For an established ileus the following will be required
    • Nasogastric tube
    • Fluid and electrolyte replacement
    • No drugs are available to reverse the condition
  • Usually resolves spontaneously after 4 or 5 days


Coleman M G, Moran B J.  Small bowel obstruction. In: Johnson C D, Taylor I eds. Recent advances in surgery 22. Churchill Livingstone, Edinburgh ,1999; 87-98.

Burke M.  Acute intestinal obstruction:  diagnosis and management.  Hosp Med 2002;  63:  104-107.

Luckey A,  Livingstone E,  Tache Y.  Mechanisms and treatment of postoperative ileus.  Arch Surg 2003;  138:  206-214.



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