GI bleeding and abdominal emergencies

Acute mesenteric ischaemia

Reviewed Nov 2026·1 references
New· views rounded down, updated weekly

High suspicion, immediate CT angiography, heparin, antibiotics and urgent revascularisation or laparotomy.

Definition
Acute mesenteric ischaemia (AMI): arterial embolism (~50%, often AF), arterial thrombosis (atherosclerosis), non-occlusive (NOMI, low-flow shock, vasopressors) or mesenteric venous thrombosis. Mortality 50-80%; time is bowel.

At the bedside

  1. 1

    Suspect

    Severe abdominal pain out of proportion to examination, AF, recent MI, vasculopathy, shock on vasopressors, hypercoagulable states; later peritonitis, bloody stools, rising lactate.

  2. 2

    CT angiography immediately

    < 1 h

    Biphasic CTA as soon as suspected; do not delay for creatinine. Lactate and D-dimer are not sensitive enough to exclude.

  3. 3

    Start treatment

    ASAP

    Fluid resuscitation, UFH 80 units/kg bolus then infusion (unless contraindicated), broad-spectrum antibiotics, NG decompression, analgesia.

  4. 4

    Revascularise

    Arterial occlusion: endovascular (thrombectomy, stent) or open embolectomy/bypass; laparotomy if peritonitis to resect non-viable bowel; planned second-look at 24-48 h.

  5. 5

    NOMI

    Treat cause of low flow, minimise vasoconstrictors, optimise cardiac output; intra-arterial vasodilator (papaverine) in specialist centres; laparotomy if peritonitis.

  6. 6

    Venous thrombosis

    Therapeutic anticoagulation; surgery if infarction; investigate thrombophilia/malignancy.

Anticoagulation in AMI

Unfractionated heparin

IV
Dose
80 units/kg bolus then 18 units/kg/h
Preparation
25,000 units in 50 mL = 500 units/mL
Target
aPTT 1.5-2.5x control
Worked example
70 kg: 5,600 units bolus, then 1,260 units/h = 2.5 mL/h
Open infusion calculator
Red flag · call your senior now
Unexplained metabolic acidosis/lactate rise in a ventilated patient on vasopressors with feed intolerance or distension: think NOMI.
Pitfall
A normal lactate does not exclude early AMI.
Pitfall
Delaying CTA because of AKI risk from contrast.
Pearl
Bowel viability can be underestimated at first operation; a second-look laparotomy is standard after revascularisation.

Calculators for this topic

Infusion rate from per-kg-per-hour dose

Pump rate for drugs dosed per kg per hour (insulin U/kg/h, midazolam mg/kg/h, propofol mg/kg/h, fentanyl mcg/kg/h, dexmedetomidine mcg/kg/h).

References

  1. 1

    Bala M, Catena F, Kashuk J, et al. Acute mesenteric ischemia: updated guidelines of the World Society of Emergency Surgery. World J Emerg Surg 2022;17:54.

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