Mesenteric Arterial Embolism

Mesenteric arterial embolism is sudden occlusion of the superior mesenteric artery (or less often another mesenteric branch) by an embolus, causing acute bowel ischaemia. It is a surgical emergency with a high mortality.

It accounts for 40% to 50% of acute mesenteric ischaemia. The embolus lodges distal to the origin of the middle colic artery, sparing the proximal jejunum and transverse colon. Most patients are over 70 years, and about 70% have atrial fibrillation. Mortality is 30% to 70%, and falls with early revascularisation.

Pathophysiology.

Emboli from the left atrium, a ventricle with recent infarction, valvular vegetations or aortic plaque block the artery, producing mucosal injury within 3 to 6 hours and transmural necrosis within 6 to 12 hours. Reperfusion injury and bacterial translocation follow.

Sudden severe abdominal pain out of proportion to the abdominal findings, vomiting, forceful bowel evacuation, then ileus, peritonitis, bloody stools and shock. A history of atrial fibrillation or recent infarction is common.

Red flags.

• Peritonitis.
• Lactate over 2 mmol/L and rising.
• Shock or multiorgan failure.
• Metabolic acidosis.

Do not delay for laboratory tests. Multiphase CT angiography (arterial and portal venous phase) is the test of choice and shows a filling defect in the superior mesenteric artery, bowel wall changes, pneumatosis and portal venous gas. Lactate, D-dimer, full blood count, creatinine, amylase and a cross-match are sent. Echocardiography and ECG look for the source.

Differential diagnosis.

• Mesenteric arterial thrombosis.
• Non-occlusive mesenteric ischaemia.
• Mesenteric venous thrombosis.
• Ruptured aortic aneurysm.
• Perforated viscus.
• Acute pancreatitis.

Resuscitate with fluids and give heparin at once. Restore blood flow by open embolectomy, endovascular aspiration or thrombolysis, or bypass, and resect non-viable bowel with second look surgery within 24 to 48 hours. Hybrid approaches are used in suitable patients.

• Heparin (unfractionated): 80 units/kg IV bolus (maximum 5,000 units) then 18 units/kg/h infusion, adjusted to an activated partial thromboplastin time of 1.5 to 2.5 times control; continue until revascularisation and then until oral anticoagulation is established; maximum bolus 5,000 units; monitor aPTT every 6 hours, platelets and bleeding; reduce in hepatic impairment and with thrombocytopenia.
• Piperacillin-tazobactam: 4.5 g IV every 6 hours for 5 to 7 days (up to 14 days after bowel resection with contamination); maximum 18 g daily; monitor renal function and counts; reduce for creatinine clearance under 40 mL/min.
• Morphine for pain: 2.5 to 5 mg IV every 4 hours as needed; maximum as limited by respiratory rate and sedation; monitor oxygen saturation and sedation; reduce by half in renal impairment and in older adults.
• Warfarin or a direct oral anticoagulant for long term prevention after revascularisation when atrial fibrillation is present: warfarin target INR 2.0 to 3.0, with enoxaparin cover; apixaban 5 mg orally twice daily (2.5 mg twice daily with two of age 80 years or over, weight 60 kg or less, creatinine 133 micromol/L or more); monitor INR or renal function and haemoglobin.

Correct acid base and electrolyte disturbance, keep mean arterial pressure at 65 mmHg or more and avoid vasopressors where possible because they worsen mesenteric vasoconstriction. Transfuse at haemoglobin 70 g/L (80 g/L with cardiovascular disease).

Monitoring. Lactate, haemoglobin, vital signs and abdominal examination every 4 to 6 hours for 48 hours; nutrition support after resection (risk of short bowel).

Referral and escalation. Vascular and general surgery urgently, interventional radiology and critical care.

Special groups. Older adults with heart failure need cautious fluid replacement and early surgical decisions.