Acute Intestinal Pseudo-Obstruction and Ileus
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Direct answer
Acute intestinal pseudo-obstruction, also called Ogilvie syndrome, is massive colonic dilatation with no mechanical blockage, usually in hospitalised or post-operative patients. The most important fact is the perforation risk once the caecum exceeds about 12 cm in diameter. Management starts with correcting electrolytes and stopping offending drugs, then intravenous neostigmine, with colonoscopic decompression or caecostomy when these fail.
What you must remember
- Definition: dilatation of the colon, mainly the caecum and right colon, with no transition point, lesion or volvulus on imaging.
- Predisposing factors: hypokalaemia and hypomagnesaemia, opioids, anticholinergic drugs, sepsis, spinal injury and major surgery, especially orthopaedic and obstetric.
- Perforation threshold: a caecal diameter of about 12 cm is the commonly cited level above which perforation risk rises sharply.
- First step: correct potassium, magnesium and calcium, and stop opioids and anticholinergic drugs.
- Drug of choice: intravenous neostigmine, given with cardiac monitoring and atropine kept at the bedside.
- Neostigmine contraindications: mechanical obstruction, asthma and bradycardia.
- Endoscopic option: colonoscopic decompression with a rectal tube for refractory cases, since it is usually effective when medical therapy has failed.
- Surgical indication: caecal perforation, bowel ischaemia or peritonitis, where caecostomy or resection is needed.
A distended abdomen after hip surgery
A 71-year-old man on morphine after a hip replacement has had no faeces or flatus for four days. Abdominal radiograph shows a dilated caecum, and the small bowel is not obviously distended.
- Exclude mechanical obstruction: CT abdomen confirms colonic dilatation without a transition point, mass or volvulus, which makes the diagnosis one of pseudo-obstruction.
- Measure the caecum: Serial radiographs or CT track the caecal diameter, since a size of about 12 cm or more threatens perforation.
- Correct the cause: Potassium, magnesium and calcium are replaced, opioids and anticholinergic drugs are stopped, and any sepsis or hypoperfusion is treated.
- Give neostigmine: Intravenous neostigmine is given slowly with heart rate monitored, and atropine is kept at the bedside in case of bradycardia.
- Decompress endoscopically: If neostigmine fails or is contraindicated, colonoscopy with a rectal tube is attempted to empty the colon.
- Operate when perforation looms: Caecostomy is done for a caecum that threatens to rupture, while peritonitis or ischaemia calls for resection.
Where the examiner tests the caecum
Most errors come from treating a dilated colon as either a mechanical blockage or as harmless.
- Trap: taking an enlarged caecum as harmless because the patient looks comfortable Correct: the caecum can perforate without warning, so a diameter of about 12 cm needs urgent review.
- Trap: relying on metoclopramide or erythromycin to clear the colon Correct: neostigmine is the agent with the best support in colonic pseudo-obstruction, and prokinetics are not reliable substitutes.
- Trap: confusing Ogilvie syndrome with paralytic ileus Correct: paralytic ileus usually involves the whole intestine, whereas Ogilvie is confined mainly to the colon.
Frequently asked questions
What caecal diameter threatens perforation in Ogilvie syndrome?
A caecal diameter of about 12 cm is the commonly cited threshold above which perforation risk rises sharply in acute colonic pseudo-obstruction. Serial radiographs or CT are used to track it, and a caecum at or above this size needs urgent surgical and endoscopic review.
Which drug is used to treat acute colonic pseudo-obstruction?
Intravenous neostigmine is the drug of choice for acute colonic pseudo-obstruction, because it reverses the cholinergic deficit that causes colonic atony. It is given with cardiac monitoring, and it is contraindicated in mechanical obstruction, asthma and bradycardia.
How does Ogilvie syndrome differ from paralytic ileus?
Ogilvie syndrome is acute colonic pseudo-obstruction with predominantly colonic dilatation, whereas paralytic ileus usually involves the whole intestine. Both are functional, so a mechanical cause must be excluded before treatment is chosen.
When is surgery needed in pseudo-obstruction?
Surgery is needed for caecal perforation, bowel ischaemia or peritonitis, and a caecostomy may be done for a caecum that threatens to rupture. Most patients with acute colonic pseudo-obstruction recover with correction of electrolytes, neostigmine and endoscopic decompression.
Which electrolyte abnormalities predispose to acute pseudo-obstruction?
Hypokalaemia and hypomagnesaemia are the best recognised electrolyte disturbances that predispose to acute colonic pseudo-obstruction, by impairing smooth muscle function. Correcting them is the first step in management, alongside stopping opioid and anticholinergic drugs.