What are the causes of non-occlusive mesenteric ischemia?

Causes of Non-Occlusive Mesenteric Ischemia (NOMI)

Non-occlusive mesenteric ischemia is primarily caused by low flow states, especially cardiogenic shock, and the use of vasoconstrictor substances, which lead to mesenteric arterial vasospasm despite patent vessels. 1

Primary Causes

Hemodynamic Factors

• Low flow states or shock, particularly cardiogenic shock, are the most common causes of NOMI 1
• Heart failure with poor cardiac output is a significant risk factor 1
• Hypovolemia leading to reduced splanchnic perfusion 1
• Renal failure, which contributes to altered hemodynamics 1
• Cardiac surgery using cardiopulmonary bypass 1
• Post-coarctation repair or after surgical revascularization for intestinal ischemia 1

Pharmacological Agents

• Vasoconstrictor medications including:
  • Vasopressors (norepinephrine, epinephrine) used in critical care settings 1
  • Vasopressin administration 1
  • Cocaine and amphetamines 1
  • Ergot derivatives, especially those used for migraine treatment 1
  • Digoxin, which can cause mesenteric vasoconstriction 1
  • Delayed absorption of overdosed antihypertensive drugs 2

Critical Illness

• Sepsis and multi-organ dysfunction 1
• Prolonged mechanical ventilation 3
• Abdominal compartment syndrome with high intra-abdominal pressure 1
• Hemodialysis 1

Pathophysiology

NOMI occurs due to SMA vasoconstriction associated with reduced splanchnic blood flow, affecting approximately 20-30% of all cases of acute mesenteric ischemia 1, 3. The pathophysiological sequence involves:

1. Initial "low flow syndrome" of mesenteric circulation 4
2. Subsequent vasoconstriction of mesenteric vessels 4
3. Reperfusion injury contributing to further ischemic damage 4, 5
4. Shunting of blood away from the intestinal mucosa 5

High-Risk Populations

• Elderly patients over 50 years of age 3
• Patients with myocardial infarction or congestive heart failure 3
• Individuals with aortic insufficiency 3
• Patients with renal or hepatic disease 3
• Post-cardiac surgery patients 3
• Critically ill patients in intensive care units 1, 5
• Patients with COVID-19 due to hypercoagulability and fibrinolysis shutdown 1

Clinical Considerations

• NOMI should be suspected in critically ill patients with abdominal pain or distension requiring vasopressor support 1
• The mortality rate remains extremely high (approximately 50%) despite advances in diagnosis and treatment 3
• Early diagnosis is challenging as symptoms may be masked in sedated ICU patients 1
• Right-sided abdominal pain with passage of maroon or bright red blood in stool is highly suggestive of NOMI 1
• Arteriography remains the gold standard for diagnosis, demonstrating characteristic mesenteric arterial vasospasm 1, 3

Treatment Approach

• Initial treatment should focus on correcting the underlying shock state and improving cardiac output/peripheral perfusion 1
• Transcatheter administration of vasodilator medications (particularly papaverine) into the area of vasospasm is indicated in patients who don't respond to systemic supportive treatment 1, 4
• Laparotomy and resection of nonviable bowel is necessary in patients with persistent symptoms despite treatment 1

Understanding these causes is crucial for early recognition and intervention in this high-mortality condition that accounts for approximately 20-25% of all cases of acute mesenteric ischemia 1.