Large Bowel Obstruction

Large bowel obstruction is mechanical interruption of colonic transit. Colorectal carcinoma is a major cause in adults, with diverticular stricture and volvulus also important.

Obstruction distal to a competent ileocaecal valve creates a functional closed loop between the obstruction and ileocaecal valve. Progressive colonic distension then places the caecum, the widest and thinnest segment, at particular risk of ischaemia and perforation.

Management depends on cause, anatomical level, bowel viability, perforation, physiological state and whether the disease is potentially curable.

• Distension and progressive absolute constipation are usually more prominent than vomiting.
• Vomiting tends to occur later than in small bowel obstruction unless the ileocaecal valve is incompetent and the small bowel also dilates.
• Pain is initially colicky. Continuous severe pain, focal tenderness, guarding or systemic toxicity suggests ischaemia or perforation.
• Ask about altered bowel habit, weight loss, rectal bleeding and iron deficiency symptoms because an obstructing colorectal malignancy may have been evolving for months.
• A rectal examination may detect a low rectal tumour, impacted stool or blood.

• Obtain full blood count, renal function, electrolytes and lactate. Anaemia may support underlying colorectal malignancy but is not diagnostic.
• CT abdomen and pelvis with IV contrast: defines the level and cause of obstruction and identifies impending perforation, ischaemia or metastatic malignancy.
• Endoscopy is not required before emergency treatment when complete obstruction, perforation or threatened bowel makes intervention urgent.

Correct dehydration and electrolyte abnormalities, keep fasting and provide analgesia. Nasogastric decompression is appropriate when vomiting or associated small bowel dilatation is significant.

Simple obstruction does not itself require antibiotics. Start broad spectrum therapy when ischaemia, perforation or secondary peritonitis is suspected. A practical regimen is:

Ceftriaxone 2 g IV every 24 hours plus metronidazole 500 mg IV every 12 hours.

Severe sepsis or major contamination may warrant:

Piperacillin tazobactam 4.5 g IV every 8 hours using extended infusion, with renal adjustment.

Peritonitis, perforation, bowel ischaemia or physiological deterioration requires urgent surgery.

For an obstructing right sided colon cancer, oncological right hemicolectomy with ileocolic anastomosis is usually appropriate when the patient is stable and tissue perfusion is satisfactory. In severe physiological compromise, diversion or resection without immediate anastomosis may be safer.

For left sided malignant obstruction, options include oncological resection with primary anastomosis, Hartmann procedure, diverting stoma, or self expanding metal stent in selected patients. NICE accepts either stenting or emergency surgery in potentially curable acute left sided malignant obstruction, while stenting is particularly useful for palliation.

A stent can convert an emergency obstruction into a planned elective resection, allowing resuscitation, staging and bowel preparation, but should be used by experienced teams because perforation compromises oncological and immediate outcomes.

Subtotal colectomy is useful when the proximal colon is severely dilated, ischaemic, perforated, contains synchronous lesions or when a more limited resection would leave questionable bowel.

The operative choice should be driven by oncological adequacy, bowel viability and physiology rather than an automatic preference for primary anastomosis.