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

    Luminal:

    • 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

    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 (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

    4 cardinal symptoms:

    • 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.

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

  • 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

    Modalities:

    • 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

    For suspected malignancy and for therapeutic relief of sigmoid volvulus.

  • Management

    Supportive and preoperative measures:

    • '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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