What are the common causes of non-occlusive mesenteric ischemia (NOMI)?

Common Causes of Non-Occlusive Mesenteric Ischemia (NOMI)

Non-occlusive mesenteric ischemia (NOMI) is primarily caused by low flow states, particularly cardiogenic shock, heart failure with poor cardiac output, and the use of vasoconstrictive medications in critically ill patients. 1

Primary Hemodynamic Causes

• Low flow states/shock: Particularly cardiogenic shock is the most common cause of NOMI 1
• Heart failure with poor cardiac output: Reduced cardiac performance leads to decreased splanchnic perfusion 1
• Hypovolemia: Severe volume depletion reduces mesenteric blood flow 1
• Renal failure: Contributes to altered hemodynamics and reduced visceral perfusion 1
• Cardiac surgery: Procedures using cardiopulmonary bypass are significant risk factors 1
• Post-surgical states: Including post-coarctation repair or after surgical revascularization for intestinal ischemia 1

Pharmacological Causes

• Vasopressors: Medications such as norepinephrine and epinephrine can cause mesenteric arterial vasospasm despite patent vessels 1, 2
• Other vasoactive drugs: Vasopressin, digoxin, cocaine, amphetamines, and ergot derivatives can precipitate NOMI 1
• Enteral nutrition: In critically ill patients on vasopressors, enteral feeding may increase risk of bowel ischemia 2

Critical Illness-Related Causes

• Sepsis and multi-organ dysfunction: Create conditions for mesenteric hypoperfusion 1
• Abdominal compartment syndrome: High intra-abdominal pressure compromises mesenteric blood flow 1
• Hemodialysis: Associated with hemodynamic shifts that can precipitate NOMI 1
• Severe coexisting illness: Commonly associated with NOMI development 2

Pathophysiological Mechanism

• NOMI occurs due to SMA (superior mesenteric artery) vasoconstriction associated with reduced splanchnic blood flow, accounting for approximately 20-25% of all acute mesenteric ischemia cases 2, 1
• The compromised SMA blood flow affects both small intestine and proximal colon due to involvement of the ileocolic artery 2

High-Risk Populations

• Critically ill ICU patients: Particularly those requiring vasopressor support 2, 1
• Elderly patients: Mesenteric ischemia incidence increases exponentially with age 3
• Patients with COVID-19: Due to hypercoagulability and fibrinolysis shutdown 1

Clinical Presentation Clues

• Unexplained abdominal distension or gastrointestinal bleeding may be the only signs in sedated ICU patients 2
• Right-sided abdominal pain with passage of maroon or bright red blood in stool is highly suggestive of NOMI 2
• In ventilated patients, any negative changes in physiology including new organ failure, increased vasopressor requirements, or nutrition intolerance should raise suspicion 2

Diagnostic Challenges

• Clinical examination and routine laboratory tests have limited value in early diagnosis 2
• Symptoms may be undetectable in approximately 25% of sedated ICU patients 2
• CTA may demonstrate bowel ischemia and free fluid despite patent mesenteric vessels 2

Understanding these causes is crucial for early identification and management of NOMI, as mortality rates remain high despite advances in critical care medicine.