Small bowel obstruction

From Ganfyd

Obstruction of the small bowel is a common diagnosis of acute abdominal pain. It must be distinguished from large bowel obstruction and a decision must be made on whether it has a mechanical or paralytic cause. Urgent surgery will be indicated if acute strangulation is suspected.

Clinical features

• Anorexia
• Nausea
• Vomiting with relief
• Colicky abdominal pain with distension
• Constipation
  • absolute constipation (i.e. absence of flatus) is diagnostic of obstruction but need not be present if obstruction is high
• 'Tinkling' bowel sounds

Compared to large bowel obstruction, patients with small bowel obstruction tend to vomit earlier, they have less distension and their pain is higher in the abdomen.

If the cause of the small bowel is ileus (for example in a post-operative patient) then pain tends to be less of a feature and bowel sounds may be absent.

A patient whose small bowel has become strangulated will be more ill than expected. The pain tends to be sharper and more constant and may be localised. The cardinal sign would be frank peritonism. There may also be fever and a raised white cell count.

Causes

• 50-70%
  • Adhesions - congenital or post-operative
• 25%
  • Herniae - internal or external
• 5%
  • Malignancy - consider caecal carcinoma obstructing the ileocecal valve
• 5%
  • Volvulus - may be around a congenital band adhesion

Investigations

• AXR
  • Abnormal gas patterns
  • A small bowel diameter of >3cm is considered abnormal on plain film
  • Abdominal X-ray gas shadows tend to be more central and there may not be any gas in the large bowel or rectum.
  • Absence of dilated loops on plain radiography does not exclude an obstruction as these are only seen in the presence of both air and fluid in the bowel.
  • Sensitivity may be between 60-80%.^[1][2]
• U&Es
  • Significant quantities of fluid can become sequestered in obstructed small bowel ('third space' losses).
  • Vomiting can also result in fluid and electrolyte losses.
• CT abdomen
  • A small bowel diameter of >2.5cm is considered abnormal
  • Superior sensitivity.^[3]
  • May be able to identify cause of obstruction (but not always, e.g. some types of adhesions), level of cut-off and other information which may influence surgical management.^[4][5]

Management

Several litres of fluids can be sequestered in the bowel and active resuscitation may involve administration of what may appear like excessive fluid.

• Conservative - 'Drip and suck'
  • NG tube
  • IV fluids & electrolytes
• Surgical
  • if strangulation = URGENT, as ischaemic bowel can lead to peritonitis and perforation.
• Water-soluble contrast. May be helpful in predicting need for surgery and may also be therapeutic.^[6]

Adhesive small bowel obstruction often settles with conservative management. Small bowel obstruction in a virgin abdomen is likely to require operative intervention.

References