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Large Bowel Obstruction

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Large Bowel Obstruction

Overview

Bowel obstruction describes obstruction leading to the prevention of normal movement of the contents in the small and large bowels. The obstruction may be mechanical (e.g. adhesions or tumours) or functional (e.g. where peristalsis is decreased, see Ileus).

Both small and large bowel obstructions are emergencies that require urgent diagnosis and treatment as they can lead to bowel ischaemia, perforation, peritonitis, sepsis, and death.

Large bowel obstruction (LBO) is most commonly caused by tumours, which make up 60% of cases.

Causes

Causes of LBO include:

  • Tumours – up to 60% of cases
  • Diverticular disease – around 20% of cases
  • Volvulus – around 5% of cases

Epidemiology

Presentation

  • Features of underlying causes:
    • Colorectal cancer tends to present over a longer period:
      • Changes in bowel habit (e.g. alternating constipation and diarrhoea) and eventually, only the passage of diarrhoea
      • Passing blood in stools
    • Volvulus tends to present acutely and is severe
  • Abdominal pain:
    • Tends to be intermittent and colicky, but occurs has longer intervals compared to small bowel obstruction
    • Continuous pain may suggest bowel ischaemia
    • Localised tenderness may suggest perforation is imminent in that area
  • Constipation and lack of passing flatus:
    • More prominent and severe, and occurs earlier than vomiting compared to small bowel obstruction
  • Abdominal distention:
    • Tends to be more significant compared to small bowel obstruction
  • Nausea and vomiting:
    • Late symptoms, also suggest a more proximal lesion
  • Palpable abdominal/rectal masses:
    • May suggest malignancy
  • High-pitched ‘tinkling’ bowel sounds – more common in early bowel obstruction
    • Trapped material and gas in the bowels lead to increased peristalsis in an attempt to clear the obstruction. Over time, as obstruction worsens, peristalsis decreases, resulting in reduced/absent bowel sounds.
    • The ‘tinkling’ sound is due to the rapid movement of material
  • Features of Peritonitis may be present if perforation occurs

Investigations

Overview

Key investigations include:

  • Abdominal X-ray:
    • Often performed first and may show dilation of the large bowel (around >6 cm for the colon and >9cm for the caecum) 
  • CT abdomen:
    • Confirms LBO and can identify aetiology

Other investigations are to look for the consequences of SBO, such as:

  • Full blood count (FBC):
    • May show leukocytosis suggesting inflammation or infection
  • Urea and electrolytes (U&Es) and blood gases:
    • May show metabolic derangements, such as:
      • Hypochloraemic, hypokalaemic metabolic alkalosis due to severe vomiting:
      • Elevated urea and creatinine in dehydration
      • Increased lactate, suggesting intestinal ischaemia

Differential Diagnoses

Small bowel obstruction (SBO)

  • Pain is generally centrally and higher up in SBO than in LBO and tends to be more severe and colicky with shorter intervals. It is more prominent as the small bowel contracts more than the large bowel.
  • Constipation occurs earlier in LBO and is more severe than in SBO
  • Abdominal distention is more common and prominent in LBO
  • In LBO, vomiting is less prominent of a feature compared to constipation.
    • Vomiting suggests a more proximal lesion and is more common in SBO.
  • In LBO, if vomiting is present, this tends to be feculent rather than bilious
  • See Small Bowel Obstruction

Ileus

  • Pain is less severe or may be sent, and is not colicky
  • Bowel movements are absent, constipation is present, and no passage of flatus
  • Bowel sounds are absent on auscultation (whereas in LBO, this is a late sign)
  • There may be an associated cause (e.g. postoperative ileus, see Ileus for more)

Management

Overview

The initial management of all patients with bowel obstruction includes:

  • Nil-by-mouth – to reduce the amount of material entering an obstructed bowel
  • IV fluids
  • Nasogastric tube with free drainage (‘drip and suck’) to remove stomach contents and decompress the bowel

The urgency of surgery depends on if evidence of bowel ischaemia, perforation, or peritonitis is present. If evidence suggesting these are not present, conservative methods may be trialled, however, many patients end up eventually requiring surgery.

Complications

As LBO progresses, blood flow to the bowel decreases, leading to ischaemia, necrosis, and perforation, followed by the leakage of bowel contents into the peritoneum, which can result in peritonitis, sepsis, shock, and death.

Prognosis

  • Many patients with LBO secondary to colorectal cancer have distant metastases, resulting in a poor prognosis

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