Large Bowel Obstruction

Question 1

Aetiology of LBO

Answer 1

1. Colorectal cancer (90%)
2. Colonic volvulus (sigmoid most commonly, also caecam)
3. Diverticulitis
4. Non-surgical causes: constipation, Olgivie syndrome (acute pseudo-obstruction)

Question 2

Pathophysiology of LBO

Answer 2

Obstruction -> proximal colon dilatation -> increased colonic P
-> decreased mesenteric BF -> mucosal oedema -> fluid and electrolytes pushed into colonic lumen

= dehydration and electrolyte imbalance

Question 3

How does perforation eventuate in LBO ?

Answer 3

Arterial blood supply decreases due to mucosal ulceration -> full thickness wall necrosis -> perforation

Sepsis can occur as bacterial has opportunity to translocate

Question 4

Common site of perforation in LBO

Answer 4

Caecum as it has the largest diameter, resulting in faecal soilage of peritoneal cavity and sepsis

Question 5

How does colonic volvulus lead to ischaemia, necrosis and perforation?

Answer 5

Once volvulus has 360 degree twist, then a closed loop obstruction is produced. Fluid and electrolyte shifts result from fluid secretion into the closed loop producing an increase in P and tension on the colonic wall that will eventually impair colonic blood supply
-> ischaemia, necrosis and perforation

Question 6

Clinical features of LBO

Answer 6

• Sudden onset colicky pain
• Each spasm lasts less than 1 minute
• Hypogastric midline pain
• Vomiting may be absent
• Constipation, no flatus (obstipation)

Question 7

Px of LBO

Answer 7

• Increased bowel sounds, especially during pain
• Distension early and marked
• Local tenderness and rigidity

Question 8

Findings of PR in LBO

Answer 8

Empty rectum, may be rectosigmoid cancer or blood

Check for faecal impaction (solid, immobile bulk of faeces)

Question 9

Findings of X-ray in LBO

Answer 9

1. Colonic distension proximal to the obstruction
2. distal collapse
3. Small bowel dilatation depending on:
   a. duration of obstruction
   b. competence of ileocaecal valve

with separation of haustral markings, especially caecal distension

Question 10

What does a sigmoid volvulus on xray show?

Answer 10

Distended loop

Question 11

What confirms Dx?

Answer 11

Gastrografin enema (contrast enema) shows obstruction site
"bird beak" in volvulus

Question 12

Rx of LBO

Answer 12

Drip and suction

Surgical referral

Question 13

Faecal occult blood test is usually ___?

Answer 13

Positive

Question 14

If unclear with xray, we should order a ___?

Answer 14

CT

Question 15

Rx of LBO

Answer 15

In all cases resuscitation and electrolyte balance.

In perforation or peritonitis, emergency laparotomy is required to prevent sepsis that involves
Hartmann’s procedure + reanastamoses of bowel 2-3 weeks later

Question 16

What is the Hartmann’s procedure?

Answer 16

resection of the affected bowel and causative lesion, bring out the remaining proximal large bowel or small bowel (if caecum resected) as a colostomy/enterostomy and oversewing the rectal stump

Question 17

Why is LBO pain hypogastric (below umbilicus)?

Answer 17

large bowl is hind gut origin

Question 18

What is the difference between bowel obstruction and ileus?

Answer 18

Bowel obstruction - pain is colicky, waxes and wanes, increased bowel sounds (tinkling)

Ileus (sleeping bowels) - pain is from distension (more consistent), absent bowel sounds