Mechanical obstruction
Aetiology
- 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%)
Pathophysiology
- 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
Investigation
- 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
Management
- 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
Investigation
- 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
Management
- 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
Bibliography
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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