Bowel Obstruction
Background
Definitions
- A mechanical blockage of the GI tract.
- Strangulated obstruction is when vessel occlusion also occurs, due to intramural pressure (e.g. hernia, volvulus). If absent, known as simple obstruction.
- Closed-loop obstruction is when there is both a proximal and distal compression. Caused by incarcerated hernias and volvulus.
Causes
- Impacted faeces.
- Gallstone ileus.
- Large polyp.
- Foreign body.
Intramural:
- Tumour
- Strictures: Crohn's or diverticulitis.
- Intussusception. Suggests tumour if it occurs in adults.
- Infarction
Extramural:
- Adhesions: surgery, IBD, or congenital bands.
- Incarcerated hernia.
- Volvulus: sigmoid, caecal, or small bowel.
- Compression e.g. tumour in 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.
Ileus and pseudo-obstruction
- Results from neurohormonal factors.
- Often follows the stress of surgery (especially GI) or systemic illness.
- Conservative management usually sufficient.
Pseudo-obstruction (large bowel):
- May be due to increased sympathetic tone (and/or reduced parasympathetic tone).
- Can be decompressed with colonoscopy.
- Aka Ogilvie syndrome when acute.
Presentation
- Abdominal pain, which may be colicky. Usually the 1st symptom.
- Vomiting. 2nd symptom in high small bowel obstruction.
- Abdominal distention. 2nd symptom in low small bowel obstruction.
- Constipation. 2nd symptom in large bowel obstruction. May be absolute (obstipation), with no flatus or faeces.
Signs:
- Abdominal tenderness.
- Tympanic percussion, unlike dullness in ascites.
- Tinkling bowel sounds in obstruction, but 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.
Investigations
Bloods
- FBC (infection, anaemia), U&E (dehydration, ↓K+ from vomiting), ↑lactate (bowel ischaemia in strangulation).
- If need to exclude hepatobiliary conditions: LFT, amylase/lipase.
- Pre-op: coag and group and save.
Imaging
- Supine abdo XR. Erect AXR is optional, but may show fluid levels.
- Barium enema can confirm caecal or sigmoid volvulus. May show bird's beak sign.
- Erect CXR: air under 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.
Abdo XR findings
Large bowel obstruction:
- General findings: dilated loops of bowel >6 cm 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 the RIF, replaced there by small bowel.
Small bowel obstruction:
- Dilated, central loops of bowel >4 cm, with complete markings across surface (valvulae conniventes).
Endoscopy
Management
- 'Drip and suck': IV fluids, and NG tube to empty stomach. Fasting to reduce pressure on GI system.
- Analgesia
- Antibiotics if perforation suspected or surgery planned.
- DVT prophylaxis.
- These measures alone can be trialled (a) for simple and incomplete obstruction, (b) if there is previous surgery, or (c) in advanced malignancy. It is sufficient for 80% of adhesions.
Surgery (laparotomy):
- Absolute indications (ASAP): generalised peritonitis, perforation, imminent perforation (caecum >10 cm), irreducible hernia, caecal volvulus.
- Relative indications (<24 hrs): 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. Still 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.
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