Bowel Obstruction

Question 1

Define bowel obstruction.

Answer 1

A mechanical blockage of the GI tract.

Strangulated obstruction is when vessel occlusion also occurs, due to intramural pressure (hernia, volvulus etc.). If this is absent, known as simple obstruction.

Closed loop obstruction is when there is both a proximal and distal compression. Can be caused by incarcerated hernias and volvulus.

Question 2

What causes bowel obstruction?

Answer 2

Luminal-
Impacted faeces
Gallstone ileus
Large polyp
Foreign body

Intramural-
Tumour
Strictures- Crohns or diverticulitis
Interssusception- suggests tumour if it occurs in adults.
Infarction

Extramural-
Adhesions- surgery, IBD or congenital bands
Incarcerated hernia
Volvulus- sigmoid, caecal or small bowel
Compression eg. tumour in a neighbouring organ

KEY CAUSES-
Adhesions and strangulated hernias are the commonest causes of small bowel obstruction. They don’t tend to affect the large bowel as it is tethered in place.

Colorectal cancer is a common cause of large bowel obstruction and must always be ruled out. Volvulus and diverticulitis are other common causes.

Question 3

Describe ileus and pseudo-obstruction.

Answer 3

Reduced bowel motility in the absence of mechanical obstruction. Similar presentation to bowel obstruction.

Paralytic ileus (small bowel)-

• Results from neurohormonal factors
• Often follows the stress of surgery (esp. GI) or systemic illness
• Conservative management usually sufficient

Pseudo-obstruction (large bowel)-

• May be due to increased sympathetic tone
• Can be decompressed with colonoscopy
• AKA Ogilvie syndrome when acute. (acute dilatation of bowel in absence of mechanical obstruction)

Question 4

How does bowel obstruction present?

Answer 4

There are 4 cardinal symptoms of bowel obstruction-

• Abdominal pain, which may be colicky.
• Vomiting
• Abdominal distention
• Constipation (may be absolute AKA obstipation with no flatus or faeces)

SIGNS
Abdominal tenderness
Tympanic percussion
Tinkling bowel sounds in obstruction, silent in ileus
Signs of cause- hernia, scars (adhesions)
Signs of perforation- fever and shock

For individuals with a competent ileocecal valve (20%), large bowel obstruction may present much sooner and there is a higher risk of perforation.

Obstructed bowel can perforate, leading to bacterial translocation and sepsis. This is commoner in large bowel obstruction usually perforating at the thin walled caecum.

Question 5

How is bowel obstruction investigated?

Answer 5

Bloods-
FBC (infection, anaemia)
U&Es (dehydration, hypokalaemia from vomiting)
Raised lactate (bowel ischaemia in strangulation)
LFTs/amylase/lipase to exclude hepatobiliary conditions
Pre-op- coag and group and save

Imaging-
Supine abdominal XR. Erect AXR is optional but may show fluid levels.
Barium enema can confirm caecal or sigmoid volvulus. May show birds beak sign.
Erect CXR- air under the diaphragm if perforated.
Abdo-pelvis CT is usually needed. May show a transition zone, beyond which there is no contrast. In strangulation, there may be bowel wall thickening or poor IV contrast uptake.

Question 6

What might be seen on abdominal XR in bowel obstruction?

Answer 6

Large bowel obstruction-

• General findings- dilated loops of bowel >6cm in diameter, with incomplete markings across surface (haustra)
• Sigmoid volvulus- coffee bean V shape pointing from LIF up towards the RUQ.
• Caecal volvulus- large bowel dilated up and out of RIF, replaced there by small bowel.

Small bowel obstruction-
-Dilated, central loops of bowel >4cm, with complete markings across surface (valvulae conniventes)

Question 7

What is the role of endoscopy in bowel obstruction?

Answer 7

For suspected malignancy and for therapeutic relief of sigmoid volvulus.

Question 8

How is bowel obstruction managed?

Answer 8

Supportive/pre-operative management-

• ‘Drip and suck’ - IV fluids and NG tube to empty stomach. Fasting to reduce pressure on GI system.
• Analgesia
• Antibiotics- for prophylaxis or sepsis
• DVT prophylaxis
• These measures alone can be trialled for a) simple and incomplete obstruction b) if there is previous surgery or c) in advanced malignancy. Sufficient for 80% of adhesions.

Surgery (laparotomy)-

• Absolute indications (ASAP)- generalised peritonitis, perforation, iminent perforation (caecum>10cm), irreducible hernia, caecal volvulus.
• Relative indications (<24hours)- failure to improve, palpable mass, virgin abdomen.

Alternatives to surgery-

• For sigmoid volvulus without peritonitis, perform rigid or flexible sigmoidoscopy, with detorsion and rectal tube insertion. Requires endoscopic or laparoscopic fixation, due to high recurrence rates (50%)
• Expanding metal stents can be used for patients unfit for surgery, or as a bridge to definitive surgery in colorectal cancer.