Acute Mesenteric Ischemia

Definition

• Acute reduction in arterial or venous blood flow to the small intestine; may result in bowel ischemia or infarct

Epidemiology

• Most commonly occurs in individuals > 60 years of age

• Prevalence in patients with acute abdomen: ∼ 1%

• Mortality: 50–70%

AMI has various etiologies, which manifest with similar clinical features despite having different underlying risk factors and pathology.

• Acute mesenteric artery embolism

  • Most common cause of AMI (causes 50% of all cases)

  • Risk factors include atrial fibrillation, myocardial infarction, valvular heart disease, and arterial interventions involving the aorta.

  • Most commonly involves the SMA

• Acute mesenteric artery thrombosis

  • Causes ∼ 25% of cases

  • Risk factors include visceral atherosclerosis, arteritis, aortic aneurysm, and aortic dissection.

• Nonocclusive mesenteric ischemia

  • Causes ∼ 20% of cases

  • Most commonly occurs in critically ill patients with low cardiac output

  • Risk factors include hypotension and the use of vasopressors, digitalis, ergotamines, or cocaine.

• Mesenteric venous thrombosis

  • Least common cause of AMI (causes < 10% of all cases)

  • Risk factors include infection, malignancy, portal hypertension, estrogen therapy, and hypercoagulability disorders. [19]

• Sudden interruption of blood flow to small bowel → intestinal hypoxia → hemorrhagic infarction and necrosis → disruption of the mucosal barrier and perforation → release of bacteria, toxins, and vasoactive substances → life-threatening sepsis

• Sites of vessel occlusion

  • SMA (∼ 90% of cases)

  • Superior mesenteric vein (< 10% of cases)

  • IMA and celiac artery (uncommon)

• Abdominal pain out of proportion to physical examination

• Diarrhea; bloody in later stages

• Nausea and vomiting, abdominal bloating

• Systemic signs of sepsis

• Peritonitis and acute abdomen in late stages

• Symptom onset and intensity may vary with the etiology of AMI. [13][15]

  • Acute mesenteric arterial embolism

    • Most acute onset and most severe pain of all AMI etiologies [15]

    • Patients may present with symptoms suggestive of an embolic source.

  • Acute mesenteric arterial thrombosis: subacute onset, less severe pain; occurs in patients with a history of abdominal angina [20]

  • Nonocclusive mesenteric ischemia: gradual onset of symptoms over several days; patients may be asymptomatic

  • Mesenteric venous thrombosis: mild, nonspecific symptoms that worsen gradually

Patients with acute mesenteric artery embolism typically present with the classic triad of severe abdominal pain, bloody diarrhea, and atrial fibrillation.

Patients with acute mesenteric artery thrombosis typically have known cardiovascular or peripheral vascular disease and/or symptoms of CMI in addition to acute symptoms.

• Indication: all patients with suspected AMI

• Findings

  • Vascular pathology: embolism, thrombosis, stenosis, or dissection of mesenteric vessels

  • Bowel wall thickening, hypoperfusion, hemorrhage

  • Bowel dilation, air-fluid levels, mesenteric fat stranding

  • Pneumatosis intestinalis

    • A radiographic finding of gas within the wall of the intestine

    • Suggests transmural ischemia or infarction

  • Portal venous gas

CTA is the test of choice for AMI.

• CBC: leukocytosis, ↑ Hct (due to volume depletion) or ↓ Hct (due to GI bleed)

• ↑ Serum lactate

• CMP: electrolyte abnormalities, ↑ AST

• Initiate supportive measures.

  • Administer supplemental oxygen.

  • Begin IV fluid resuscitation.

• Insert a nasogastric tube and keep the patient NPO.

• Start broad-spectrum IV antibiotics: See “Empiric antibiotic therapy for intraabdominal infections.”

• Begin parenteral anticoagulation with unfractionated heparin.

• Surgical

  • Bowel resection (of necrotic segments)

  • Revascularization: open embolectomy and/or mesenteric bypass surgery

  • Damage control surgery (with or without temporary abdominal closure): for critically ill patients

• Endovascular revascularization

  • Mechanical removal of the emboli or thrombus

  • Angioplasty with or without stenting of the mesenteric artery

  • Catheter-directed intraarterial infusion of thrombolytics or vasodilators (e.g., papaverine)

Emergency laparotomy is indicated if there are signs of peritonitis, intestinal infarct, or hemodynamic instability. [13][15]

Immediate anticoagulation and endovascular revascularization may be considered in hemodynamically stable patients with AMI and no signs of advanced bowel ischemia.

• Recommend lifestyle modifications for secondary prevention of ASCVD.

• Optimize treatment of the underlying disease (e.g., Afib, HFrEF).

• Lifelong anticoagulation is typically recommended for patients with embolic AMI.