Bowel Obstruction

Small bowel obstruction (SBO)

Demographics: occurs in 1 in 11 people at some point after abdominal surgery.

Murtagh’s triad: colicky central pain + vomiting + distension suggests small bowel obstruction.

History: common causes are post-operative adhesions, tumours, hernias, and inflammatory bowel disease. Abdominal pain; nausea and bilious vomiting; constipation and reduced/absent flatus; abdominal distension; no oral intake/anorexia.

Examination: check BP, pulse, temperature. Signs of complication (bowel perforation or necrosis) may include fever, tachypnoea, tachycardia, hypotension, decreased urine output, and severe or rebound tenderness. Abdominal distension; sharp, tinkling bowel sounds; generalised tenderness; abnormal abdominal movement (visible peristalsis); abdominal mass.

Investigations: supine and erect abdominal X-ray are often done initially — useful for diagnosing perforation needing immediate surgery (step-ladder fluid levels). CT abdomen/pelvis to diagnose SBO — use IV contrast if feasible, avoid oral contrast if complete SBO is suspected (water-soluble oral contrast has a role in diagnosis/management if the patient isn’t vomiting); CT identifies the level of obstruction (transition point) and the aetiology. Bloods: FBC, UEC and CMP, blood gas (lactic acid as an ischaemia marker).

Management: admit to hospital or transfer for ED assessment. Partial obstructions often resolve without surgery (within 2–5 days); complete obstruction may also resolve without surgery. IV fluids and nil by mouth; replace electrolytes as required; IV analgesia and antiemetics; decompression with a nasogastric tube; may require surgical intervention. Monitor for complications — bowel necrosis, perforation, peritonitis.

Large bowel obstruction (LBO)

Demographics: far less common than SBO — likely due to neoplasia in 50–60% of cases.

Murtagh’s triad: colicky pain + distension ± vomiting suggests large bowel obstruction.

History: colicky abdominal pain, distension, failure to pass flatus and stool.

Causes: malignancy (colorectal carcinoma 50–60%; pelvic tumours, direct spread, or metastatic disease); colonic diverticulitis; volvulus (caecal 1–3%, sigmoid 3–8%); ischaemic stricture; faecal impaction/faecaloma (the most common cause in debilitated elderly patients); hernias (uncommon).

Examination: signs of peritonism, sepsis, and shock develop if perforation occurs. Abdominal distension, tympanic abdomen, generalised pain; reduced bowel sounds.

Investigations: abdominal X-ray — colonic distension with a collapsed distal colon, free intra-abdominal gas (pneumoperitoneum). CT confirms the diagnosis, localises the obstruction, and in most cases identifies the cause.

Management: hospital admission — IV fluids, IV antibiotics if required, decompression and surgery. Management largely depends on the underlying cause.