Small Bowel Obstruction

Key facts

• A surgical emergency
• 5% of all surgical admission

Pathophysiology

• Obstruction → Dialation of the small bowel above the level of obstruction → causes mucosal oedema → initially causes venous followed by arterial blood flow obstruction → ischaemia ensues
• ischeamia → infarction and perforation
• Ischaemia → bacterial translocation

Aetiology

Based on the most common presentation

• Adhesions (60%)
• Strangulated hernia (20%)
• Malignancy (5%)
• Volvulus (5%)

Aetiology based on anatomy

• Luminal (inside the wall)
  • Foreign body
  • Gallstones (gallstone ileus )
  • Bezoars (clump of swallowed hair)
• Intraluminal (in the wall)
  • Crohn’s stricture
  • Small bowel tumour
  • Congenital atresia
  • Malignancy (rare in small bowel)
• Extraluminal (outside the wall)
  • Adhesion (most common)
  • Hernia (second most common)
  • Intussusception
  • Congenital adhesion band
  • External compression (neoplastic mass)

Signs and symptoms

4 cardinal features

• Colicky abdominal pain
• Distention
• Vomiting
• Absolute constipation (no faeces and flatus)

Prominence and timing of these features depends on the site of obstruction

• Gastric outlet obstruction- vomiting early and +++; virtually no distension +; late absolute constipation; pain higher in the abdomen
• Small bowel- Vomiting early ++; distension ++, pain higher in the abdomen
• Distal colon- Vomiting very late +; Distension +++; early absolute constipation +++; pain lower in the abdomen and often constant

Examination

Investigations

• All of these investigations are first line
• Bloods: FBC, U&Es, LFT, amylase/lipase, Capillary BM, CRP, Clotting, G&S, ABG/VBG
• Abdominal x-ray: >3cm dilation of small bowel which can be identified by valvulae conniventes (bands which completely traverse the bowel), and bowel position centrally on the film
• Erect CXR: to r/o perforation
• Gastrograffin follow through (consider after failed conservative management)
• CT: to identify site and cause of obstruction

Management

• Mnemonic: Drip (IV fluid) and Suck (NG tube)
• Initial management for every patients
  1. Fluid resuscitation (‘drip)
     • Can be severely dehydrated due to vomiting, third space loss and sequestration of fluid into the dilated bowel (up to 6- 8 litres)
     • Accurate fluid balance monitoring which may mean urinary catheter insertion
  2. Bowel decompression i.e. NG tube (‘suck’)
  3. Analgesia e.g. Morphine SC/IM
  4. Determine the cause of obstruction
• To surgery or not to surgery? (laparotomy + resection)
  1. Adhesional obstruction
     • usually resolves with conservative management
     • If not settled by 48 hours or evidence of ischaemia or peritonitis, then surgery
  2. All other cause
     • Absolute indication for surgery: generalised or localised peritonitis, visceral perforation, irreducible hernia
     • Relative indication for surgery: palpable mass lesion, virgin abdomen, failed conservative management,50% in 3 months and 95% in 1 year