Large Bowel Obstruction

Large bowel obstruction is an emergency condition that requires urgent intervention.

Aetiology

  • 50-60% of LBO is caused by a colorectal carcinoma (most commonly in the sigmoid colon)
  • Strictures secondary to diverticular disease can also cause LBO
  • A sigmoid volvulus (often a cause of ‘closed loop’ obstruction)
    • More commonly occurs in the elderly with a history of constipation/laxative use (indeed impaction/obstipation can also be a cause of LBO)
  • Large bowel pseudo-obstruction can also occur (in a similar way to SBO- i.e. paralysis of the large bowel)
  • Rarer causes include ischaemic bowel, inflammatory bowel disease, hernia

Pathophysiology

  • Mechanical obstruction causes dilatation above the obstruction.  The build up in pressure eventually blocks lymphatic and venous return, causing bowel oedema and ischaemia.  This increases the permeability of the bowel, which causes loss of fluids into the lumen and increases the likelihood of infection.  Ischaemia can lead to perforation.
  • Closed loop obstruction
    • Caused by obstruction at 2 points
      • e.g. sigmoid volvulus; 2 points of stricture/tumour (rarer); or more commonly, a single point of obstruction with a competent ileocaecal valve
        • the latter is particularly dangerous because it allows secretions to enter the large bowel (9l/day) but does not let it exit.  This can cause rapid progression of the LBO, often with less specific symptoms.
  • Acute colonic pseudo-obstruction (Ogilvie syndrome)
    • Pathogenesis not fully understood but thought to be an imbalance of autonomic control causing paralysis of bowel movement.  It is known to be associated with many medical/surgical conditions involving the large bowel and is more commonly seen in old people.

Presentation

  • Abdominal pain (severe, crampy, diffuse, nonlocalised)
    • May be acute (volvulus) or sub-acute/slower onset (tumour) or may have had previous episodes of diverticulitis type pain (stricture)
  • Abdominal distention
  • Constipation (remember to ask about flatus too- complete obstruction will present with the absence of passing wind)
  • Nausea and vomiting (often a late sign as bowel contents backs up into the more proximal small bowel)
  • Bowel sounds may be present early on but may be reduced/absent later
  • The abdomen may be hyperresonant to percuss
  • The abdomen may be tender, and if there are any signs of peritonism (fever, severe tenderness, rigidity), perforation should be suspected and the patient taken to theatre as soon as possible.

Investigations

  • As with most patients, bloods should be taken (and IV access established)
    • FBC and U&Es are critical (blood loss and dehydration need to be investigated)
  • CXR- look for air under the diaphragm (perforation)
  • AXR- the colon can be massively distended (normally <6cm)
  • CT abdo is the gold standard and will help to identify cause.
  • Barium studies may be useful in differentiating between complete, partial and pseudo obstruction and can also help identify perforation but may not be suitable for the acute patient

Management

  • As with other acute scenarios: ABCDE
    • Oxygen therapy is usually given
    • Most, if not all, patients will require some form of volume resuscitation (either saline or Hartmann’s)
  • An NG tube with suction should be considered in vomiting patients with abdominal distention
  • Management of the obstruction
    • Often surgical, but ultimately depends on the cause.  Criteria for surgery include:
      • Any indication of perforation; closed loop obstruction; volvulus; bowel ischaemia
    • Tumours causing obstruction can be managed by inserting a colonic stent
      • NB Not to be used in low rectal lesions; right sided colonic obstruction; if there is perforation
      • Otherwise, operative management is more suitable.  This usually involves resection of the tumour and associated bowel
    • Pseudo-obstruction and impaction obstruction do not require surgical intervention.  The formed requires resuscitation and rest only (+ management of any underlying disorders).  Impaction should be treated (usually with laxatives). 
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