Small/Large Bowel Obstruction

Question 1

What causes it?

Answer 1

Small bowel
-	Adhesions
-	Hernias
Large bowel
-	Colon ca
-	Constipation
-	Diverticular stricture
-	Volvulus – sigmoid/caecal
Rarer causes 
-	Crohn’s stricture
-	Gallstone ileus
-	Intussusception
-	TB (developing world)
-	Foreign body

Question 2

How does it present?

Answer 2

CARDINAL FEATURES = Vomiting, colicky pain, constipation, distension.

• Vomiting, nausea, anorexia.
• Fermentation of intestinal contents in established obstruction causes ‘faeculent’ vomiting.
• Colic occurs early.
• Constipation need not be absolute (i.e. no faeces or flatus passed) if obstruction is high, though in distal obstruction nothing will be passed.
• Abdominal distension is marked as the obstruction progresses.
• Active, tinkling bowel sounds.

Difference between small and large bowel obstruction
- SBO – vomiting occurs earlier, distension is less, pain higher in the abdomen.
- LBO – pain is more constant.
- AXR
 In SBO, AXR shows central gas shadows with valvulae conniventes that completely cross the lumen and no gas in the large bowel.
 In LBO, AXR shows peripheral gas shadows proximal to the blockage (eg. In caecum) but not in the rectum, unless PR has been done. Large bowel haustra do not cross all the lumen’s width.

Ileus or mechanical obstruction?
- Ileus is functional obstruction from reduced peristalsis – no pain and bowel sounds absent.

Question 3

Investigations?

Answer 3

PR, AXR, CXR, bloods, CT

Question 4

Treatments?

Answer 4

General
- Cause, site, speed of onset and completeness of obstruction determine definitive therapy: strangulation and LBO require surgery; ileus and incomplete SBO can be managed conservatively.

Immediate Action

• NGT and IV fluids to rehydrate and correct electrolyte imbalance.
• Also: analgesia, blood tests (inc. amylase, FBC, U&E), AXR, erect CXR, catheterize to monitor fluid status.

Further Imaging

• CT finds the cause and level of obstruction.
• Maybe colonoscopy in some instances of suspected mechanical obstruction.

Surgery

• Strangulation needs emergency surgery, as does ‘closed loop obstruction’.
• Stents may be used for obstructing large bowel malignancies either in palliation or as a bridge to surgery in acute obstruction.
• Small bowel obstruction secondary to adhesions should rarely lead to surgery.