What is Non-Occlusive Mesenteric Ischemia (NOMI)?
Non-occlusive mesenteric ischemia (NOMI) is acute intestinal ischemia caused by superior mesenteric artery vasoconstriction and reduced splanchnic blood flow in the absence of a physical blockage (embolus or thrombus) in the mesenteric vessels. 1
Pathophysiology
NOMI results from severe vasoconstriction of the superior mesenteric artery that persists even after the precipitating event is corrected, leading to critically reduced intestinal perfusion without any anatomic obstruction. 1, 2 The compromised SMA blood flow typically affects both the small bowel and proximal colon through involvement of the ileocolic artery. 1
Epidemiology and Clinical Context
- NOMI accounts for 20-30% of all acute mesenteric ischemia cases, with recent data showing an increase to approximately 25% due to improved intensive care allowing more critically ill patients to survive longer. 1, 3, 2
- Mortality rates approach 50%, making this a life-threatening condition requiring urgent recognition. 4, 2
High-Risk Patient Populations
NOMI occurs almost exclusively in critically ill patients with specific risk factors: 1
- Cardiac failure (the most common precipitant, often triggered by sepsis)
- Recent cardiac surgery (particularly procedures using cardiopulmonary bypass) 4
- Septic shock requiring vasopressor support 1
- Severe hypovolemia 1
- Hemodialysis patients 4
- Advanced age with cardiovascular comorbidities 4
Clinical Presentation Pitfalls
The key diagnostic challenge is that NOMI often presents with subtle or absent clinical signs in sedated ICU patients. 1 Critical warning signs include:
- Unexplained abdominal distension or gastrointestinal bleeding may be the only manifestations in approximately 25% of cases 1
- New onset organ failure or increased vasopressor requirements in ICU patients 1
- Nutrition intolerance in critically ill patients 1
- Bacteremia and diarrhea following cardiopulmonary resuscitation 1
- Right-sided abdominal pain with passage of maroon or bright red blood per rectum 1
Diagnostic Approach
CTA remains the primary diagnostic modality, showing bowel ischemia and free fluid in the presence of patent mesenteric vessels (distinguishing it from embolic or thrombotic causes). 1 However, selective mesenteric angiography is the gold standard for definitive diagnosis, demonstrating characteristic findings of peripheral vasoconstriction without proximal occlusion. 5, 2
Key Distinguishing Features from Other AMI Types
Unlike the other three causes of acute mesenteric ischemia:
- No embolus (which would lodge 3-10 cm distal to SMA origin) 1
- No thrombosis at the SMA origin (which requires pre-existing atherosclerotic disease) 1
- No venous thrombosis (which would show thrombus in the superior mesenteric vein) 1
- Vessels remain patent on imaging, but functional blood flow is severely compromised 1, 2
Treatment Principles
The cornerstone of NOMI management is intraarterial vasodilator therapy, not surgical intervention (unless bowel necrosis has already occurred). 5, 2 This represents a fundamental difference from embolic or thrombotic mesenteric ischemia, where revascularization is the primary treatment. Vasospasm persists even after correcting the precipitating cause, making direct intraarterial vasodilator administration the only proven effective therapy for early NOMI without bowel infarction. 2