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Colorectal Surgery

Acute Mesenteric Ischaemia

Sudden loss of blood supply to the small bowel, most often an embolus from the heart lodging in the superior mesenteric artery, causes rapidly progressive transmural infarction; the hallmark is severe pain out of proportion to a soft abdomen, and survival depends on revascularising the gut before it dies.

In a nutshell

Acute mesenteric ischaemia is sudden loss of small-bowel blood supply, most often an SMA embolus from atrial fibrillation, causing rapid transmural infarction. The hallmark is pain out of proportion to a soft abdomen. Diagnosis is urgent CT angiography (do not wait for lactate), and treatment is urgent revascularisation and resection of dead bowel. Mortality is high.

Classic presentation

An older patient with atrial fibrillation develops sudden severe central abdominal pain out of proportion to a soft, barely tender abdomen, later becoming peritonitic and acidotic.

Key points

  • Pain out of proportion to a soft abdomen is the early hallmark; peritonism and a rising lactate are late.
  • Embolism from atrial fibrillation is the commonest cause; other mechanisms are thrombosis, non-occlusive low-flow and venous thrombosis.
  • CT angiography is the diagnostic test and must not be delayed; a normal early lactate does not exclude it.
  • Treatment is urgent revascularisation (surgical or endovascular) plus resection of non-viable bowel, often with a second-look laparotomy.
  • Mortality is high and rises steeply with delay to revascularisation.

First-line investigation

Urgent CT angiography of the mesenteric vessels; serum lactate helps but rises late.

Management

Resuscitate and activate the pathway

  • Treat suspected acute mesenteric ischaemia as a time-critical emergency: resuscitate, give early broad-spectrum antibiotics, and involve senior surgery, vascular, interventional radiology and critical care.1,2

Image without delay

  • Obtain urgent biphasic CT angiography with arterial and portal-venous phases; do not wait for lactate or renal-function reassurance when suspicion is high.1,2

Restore flow and preserve bowel

  • Use endovascular or open revascularisation according to anatomy and expertise, resect only non-viable bowel, and consider a planned second look when viability is uncertain.1,2

Operate for infarction

  • Peritonism, perforation, shock with suspected necrosis or irreversible CT features require immediate operative assessment without further diagnostic delay.1,2

Treat cause and support recovery

  • Treat the embolic, thrombotic, low-flow or venous mechanism with specialist guidance, and plan critical-care, nutritional and intestinal-failure follow-up after resection.1,2,3

Exam traps

  • A normal lactate early does not exclude acute mesenteric ischaemia.
  • A soft abdomen with severe pain is the classic early picture; waiting for peritonism means waiting for infarction.
  • Do not confuse it with ischaemic colitis, which is a low-flow colonic injury that is usually self-limiting.
  • New atrial fibrillation with sudden severe abdominal pain is an embolic SMA occlusion until proven otherwise.

Illustrations

Ischaemic small bowel on CTAxial contrast CT showing multiple dilated fluid-filled small-bowel loops with wall thickening, an imaging appearance of acute mesenteric ischaemia.James Heilman, MD, Wikimedia Commons · CC-BY-SA-3.0

Key sources

  1. ESVS 2025 Guidelines on Diseases of the Mesenteric and Renal Arteries and Veins (Current specialist vascular guideline covering chronic and acute arterial mesenteric ischaemia, non-occlusive disease and mesenteric venous thrombosis; includes urgent biphasic CT angiography, specialist-centre care, revascularisation strategy, antibiotics, anticoagulation and surgery.)
  2. World Society of Emergency Surgery: Acute mesenteric ischaemia updated guidelines (International emergency-surgery guideline used because there is no dedicated NICE or UK national acute-mesenteric-ischaemia guideline; covers diagnosis, resuscitation, antibiotics, urgent surgery, revascularisation and second-look assessment.)
  3. BNF online: current anticoagulant, analgesic and antimicrobial prescribing (Use the current BNF and local surgical, vascular and antimicrobial protocols for drug selection, dosing, renal adjustment, contraindications, interactions, duration and monitoring; no fixed regimen is reproduced here.)
  4. NICE NG89: Venous thromboembolism in over 16s (NICE VTE-prevention guidance relevant to peri-operative risk assessment and prophylaxis when safe; it is not a disease-specific treatment guideline for acute mesenteric ischaemia.)

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.