Small Bowel Obstruction
This is a mechanical or functional obstruction of the small bowel, preventing normal bowel transit, and is a surgical emergency
Epidemiology
Accounts for about 5% of all surgical emergencies.
Causes
- Adhesions
- Hernia
- Tumour
- Intussusception
- IBD
- Volvulus
- Foreign bodies – e.g. a gallstone in gallstone ileus
Pathophysiology
The bowel becomes obstructed for one of the above reasons, and becomes proximally distended. Initially this can cause increased peristalsis on either side of the obstruction and so cause diarrhoea. The intraluminal pressure will continue to rise due to the accumulation of secretions and swallowed air. Increased hydrostatic pressure in the capillary beds will cause third spacing into the intestinal lumen and contribute to dehydration. The degree of vomiting will depend on how proximal the obstruction is.
Presentation
- Pain – usually colicky pain, though if due to strangulation, the progressive ischaemia may give rise to constant pain
- Nausea
- Vomiting – if there is bilious vomiting, and a shorter history of pain, the obstruction is more likely to be proximal
- Diarrhoea – an early finding
- Absolute constipation – a later finding
- Fever
- Ask about previous abdominal surgery
- Ask about a history of malignancy elsewhere – primary small bowel neoplasm is not common
On examination
- Abdominal distension – more pronounced with distal obstruction
- Increased bowel sounds initially – high-pitched tinking BS, and then later, absent bowel sounds
- Look for hernias; stoma if present
- Check for signs of bowel ischaemia – fever, tachycardia, signs of peritonitis
Differentials
- SBO
- Gastroenteritis
- Small bowel ischaemia
- Perforation
- Pancreatitis
- Rule out MI
Investigations
- FBC – raised WCC
- U&E
- Group and cross-match
- PFA – show the valvulae conniventes extending the full width of the lumen; loops of small bowel central on film
- Erect CXR – air under diaphragm?
- Barium studies may be useful
- CT is useful especially if the diagnosis isn’t clear and to assess the exact level of the obstruction
Treatment
- NPO
- NG
- IV Fluids
- Antibiotics to cover gram negative and anaerobes
- May need an anti-emetic
- Analgesia
- Adhesive obstructions often resolve without surgery
- Surgery may be required