• Mesenteric ischemia is uncommon cause of abdominal pain:
  • Less than 1 in 1000 hospital admissions.
• However, mortality rate is high if diagnosis is delayed or missed.
• Clinical starting point:
  • Have high index of suspicion and low threshold to CT, especially in patient presenting with acute abdominal pain and cardiovascular risk factors.
• Clinical endpoint:
  • Disposition depends on etiology of ischemia, with better prognosis for venous rather than arterial etiology, and chronic rather than acute ischemia.
  • Patients with acute arterial ischemia are often very ill and prognosis guarded.
• Chronic mesenteric ischemia is often caused by atherosclerosis and can be debilitating due to postprandial pain, food fear, and weight loss.
  • However, not acutely fatal and will not be considered further in this clinical summary.
• Etiology:
  • Mesenteric arterial occlusion:
    • Embolic source: 40-50%
    • Thrombotic occlusion: 20-35%
    • Dissection: <5%
  • Mesenteric venous thrombosis: 5-15% of cases
    • Primary (idiopathic)
    • Secondary causes: thrombophilia, trauma, local inflammatory changes from pancreatitis, diverticulitis, inflammation, or infection, etc.
  • Nonocclusive mesenteric ischemia: 5-15% of cases
    • Cardiac insufficiency or low-flow states.
    • Increasingly identified in patients undergoing hemodialysis.

• Risk factors:
  • Mesenteric arterial occlusion:
    • Arterial embolism: atrial fibrillation and other atrial tachyarrhythmias, recent MI or other embolic events (e.g.: stroke), less commonly cardiac valvular disease, endocarditis, proximal aneurysm, recent catheter-based angiography.
    • Arterial thrombosis: atherosclerosis.
  • Mesenteric venous thrombosis:
    • DVT
    • Hx of cancer, chronic liver disease.
    • Recent abdominal surgery.
    • Thrombophilia or family history of clotting disorders.
  • Nonocclusive mesenteric ischemia:
    • Low-flow states: severe heart failure, severe sepsis.
    • Recent cardiac surgery.
    • Hemodialysis.

• History:
  • Look for evidence of atherosclerotic and vascular disease on history:
    • PAD, CVS, CAD
    • History of atrial fibrillation and recent MI hints to possible embolic source.
    • History of low-flow states such as severe cardiomyopathy points to non-occlusive source.
  • Wide spectrum of nonspecific patient presentations makes the diagnosis challenging:
    • Can vary from pain out of proportion to vague abdominal pain to absent abdominal symptoms altogether.
  • Classic triad: look for sudden, severe abdominal pain, gut emptying with vomiting/diarrhea, underlying cardiac disease.
  • Embolic source more likely if acute onset of ischemic symptoms in previously asymptomatic patient, with no prodrome and rapid progression.
  • Thrombotic source more likely if sudden worsening of symptoms in a patient with long history of intestinal angina.
• Physical exam:
  • Nonspecific
  • Classically, pain out of proportion to exam should prompt the physician to consider mesenteric ischemia.
  • Absent bowel sounds, fecal occult blood are late findings.
  • Tachycardia, tachypnea, hyper or hypothermia.
  • Hypotension is late and ominous finding.
• Investigations:
  • CT angiography is the gold standard,
  • CBC: elevated WBC may indicate full-thickness injury to bowel wall or ischemia with bacterial translocation,
  • Electrolytes
  • Metabolic acidosis
  • Lactate: often elevated late in disease; significant elevation associated with patient mortality,
  • ECG: look for arrhythmias such as atrial fibrillation.
  • Imaging: abdominal x-ray, duplex ultrasound, CT angiography.
    • X-ray may show bowel distention with air-fluid levels, progression to necrosis manifests as pneumatosis intestinalis (linear collections of air in bowel wall).
    • Duplex ultrasound has high sensitivity and specificity but can be difficult to obtain due to degree of pressure applied. It is best reserved for chronic mesenteric ischemia.
    • CT angiography has 95-100% accuracy and has become recommended method of imaging for diagnosis of visceral ischemic syndromes.
      • Decreased or absent bowel wall enhancement is most specific CT sign of intestinal ischemia.
      • Non-specific findings taken together are more specific for acute mesenteric ischemia: bowel wall thickening, mesenteric edema, luminal dilatation of intestine, portal venous gas.

Figure taken from article by Blaser et al. A clinical approach to acute mesenteric ischemia. Current Op in Crit Care. 2021; 27: 183-92

Mesenteric Arterial Ischemia:

• Initial management:
  • Aggressive IV fluids and electrolyte monitoring, AVOID vasopressors.
  • IV broad-spectrum antibiotics.
  • IV unfractionated heparin: decision should be made with surgical consult.
  • NPO in acute mesenteric ischemia.
  • Enteral nutrition or parenteral nutrition in chronic mesenteric ischemia.
• Stable: endovascular intervention with pharmacomechanical thrombolysis (embolic disease) or stenting (thrombotic disease).
• Unstable: laparotomy with thromboembolectomy, mesenteric bypass and/or retrograde mesenteric stent, and bowel resection, if necessary.

Mesenteric Venous Thrombosis:

• Stepwise approach:
  • If symptoms are mild and no CT evidence of compromised bowel perfusion, LMWH and transition to oral anticoagulation.
  • If symptoms are severe and CT shows edematous bowel, continuous IV UFH.
  • If medical treatment fails, options include percutaneous mechanical thrombectomy and/or catheter-directed thrombolysis via transhepatic access.
• Any evidence of peritonitis, stricture, GI bleed should prompt exploratory laparotomy.

Nonocclusive Mesenteric Ischemia:

• Ensure hemodynamic stability: fluid resuscitation and electrolytes, blood transfusion.
• Manage underlying cause (HF or sepsis).
• IV infusion of vasodilatory and antispasmodic agents can be used:
  • Papaverine 60 mg bolus followed by infusion (30-60 mg/hr) with repeated angiograms obtained every 24 hours.
• Laparotomy when bowel necrosis is suspected.

Long-term management:

• Aspirin lifelong in all patients who undergo endovascular or open repair.
• Clopidogrel for 1-3 months after endovascular repair.
• DOAC indicated in patients with atrial fibrillation, MVT.
• Lifestyle management: smoking cessation, exercise, manage dyslipidemia and hypertension.

1. EM Board Bombs: https://www.emboardbombs.com/papers/2020/3/9/the-abominable-pain-acute-mesenteric-ischemia

   Emergency Medicine Cases Podcast: https://emergencymedicinecases.com/episode-42-mesenteric-ischemia-pancreatitis-3/

   Life in the Fast Lane: https://litfl.com/mesenteric-ischaemia/

    

   
   

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8. Zhao Y, Yin H, et al. Management of Acute Mesenteric Ischemia: A Critical Review and Treatment Algorithm. Vasc and Endovasc Surg. 2016; 50(3): 183-92.