Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.
2 min synopsisUK scopeSources checked 8 Sept 2026Clinical review pending
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Toxic dilatation can perforate without warning
Fever, tachycardia, hypotension, abdominal distension and tenderness with acute colitis and non-obstructive dilatation constitute a surgical emergency; transverse-colon diameter above 5.5 cm on plain radiography is a supporting criterion. Guarding, rising lactate, free gas or worsening organ dysfunction indicates threatened or actual perforation.
Action: Start ABCDE resuscitation, keep nil by mouth, obtain large-bore access and cross-match, correct fluid and electrolyte losses, stop opioids, anticholinergics and antimotility drugs, send infection tests, begin cause-specific treatment and urgent broad-spectrum antibiotics when sepsis or perforation is suspected, and involve colorectal surgery and critical care immediately.
Synopsis
Recognise toxic megacolon as acute colitis with systemic toxicity and non-obstructive colonic dilatation, stabilise without provoking perforation, treat the inflammatory or infectious cause, and move promptly to subtotal colectomy when physiology or the abdomen deteriorates.
Toxic megacolon combines acute severe colitis and systemic toxicity with non-obstructive colonic dilatation; transverse-colon diameter above 5.5 cm on plain radiography is a practical criterion, but dilatation alone is not the diagnosis.
Examine repeatedly for distension and peritonism, obtain FBC, CRP, renal profile, electrolytes, albumin, lactate, cultures, C difficile tests and serial abdominal imaging.
Stop loperamide, codeine, other opioids and anticholinergic drugs because impaired motility can worsen dilatation; avoid bowel preparation, barium enema and full colonoscopy.
Key red flags
Generalised guarding, rebound, free intraperitoneal gas or a rapidly rising lactate suggests perforation or bowel ischaemia and requires immediate operative source control.
Increasing colonic diameter, new loss of bowel sounds, worsening pain or progressive distension despite treatment indicates failure even before laboratory markers deteriorate.
Hypotension, oliguria, confusion, hypoxaemia or escalating vasopressor need signals systemic decompensation and removes time for prolonged medical rescue.
Ongoing severe colorectal haemorrhage with transfusion requirement is an independent indication for urgent surgical control.
Investigation priorities
01
Contrast CT abdomen and pelvisFirst stepPreferred
preferred initial imaging when clinically suspected toxic megacolon can be assessed without unsafe transfer; define perforation, ischaemia, collection, mechanical obstruction and alternative pathology.
Management branches
Worked case: toxic dilatation during ASUCRecognise medical failure and reach emergency source control
A 36-year-old receiving intravenous hydrocortisone for acute severe ulcerative colitis develops increasing distension and pain. Temperature is 39.0°C, pulse 126/min, blood pressure 94/58 mmHg and lactate 2.8 mmol/L; radiography shows transverse colon 7.2 cm without free gas.
Diagnose toxic megacolon from severe colitis, toxicity and non-obstructive 7.2 cm dilatation; call colorectal surgery, anaesthesia and critical care now rather than waiting for the next routine ASUC review.
Keep nil by mouth, establish large-bore intravenous access, cross-match blood, correct potassium and volume deficits and insert urinary monitoring; stop codeine prescribed overnight and avoid colonoscopy or bowel preparation.
Key medicines
Hydrocortisone for ulcerative-colitis toxic megacolonWhen toxic megacolon complicates acute severe ulcerative colitis without perforation, give hydrocortisone 100 mg IV every 6 hours; administer each reconstituted injection over 1–10 minutes while urgent surgical assessment continues.Do not use as treatment for infectious colitis alone. Exclude untreated systemic fungal infection and avoid live vaccine at immunosuppressive doses; monitor infection, glucose, blood pressure, mental state, potassium and fluid balance. Review CYP3A4 modifiers, warfarin and potassium-depleting medicines, and do not prolong treatment because one examination is temporarily unchanged.
Oral vancomycin for life-threatening C difficile infectionUnder specialist advice give vancomycin 500 mg orally every 6 hours WITH metronidazole 500 mg IV every 8 hours, both for 10 days, for life-threatening CDI. Use two 250 mg vancomycin capsules per dose for the selected product; the 2 g/day maximum is not exceeded. This oral preparation treats the colonic lumen and must not be replaced by IV vancomycin for CDI.Severe intestinal inflammation can increase systemic absorption, especially with renal impairment. In this worked patient with creatinine twice baseline, monitor serum vancomycin concentration and serial renal function; also review nephrotoxic or ototoxic medicines and stop for a severe cutaneous reaction.
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 8 Sept 2026; clinical approval remains outstanding.