Mesenteric Ischemia 

Definition

Mesenteric ischemia refers to insufficient blood flow to the small intestine and/or colon, resulting in intestinal hypoxia, mucosal injury, transmural infarction, sepsis, and death if untreated.

It is a time-critical vascular emergency with mortality ranging from 40–80%, depending on etiology and delay in diagnosis.

 

Classification 

1. Acute Mesenteric Ischemia (AMI)

Sudden interruption of intestinal blood flow
→ Most lethal form

2. Chronic Mesenteric Ischemia (CMI)

Progressive atherosclerotic narrowing
→ “Intestinal angina”

3. Mesenteric Venous Thrombosis (MVT)

Venous outflow obstruction
→ Subacute presentation

4. Non-Occlusive Mesenteric Ischemia (NOMI)

Low-flow state without vessel occlusion
→ Common in ICU


Mesenteric Vascular Anatomy 

  • Celiac artery (T12) – foregut
  • Superior mesenteric artery (SMA, L1) – midgut
    → Most commonly involved
  • Inferior mesenteric artery (IMA, L3) – hindgut

Extensive collateral circulation (pancreaticoduodenal arcade, arc of Riolan) explains delayed symptoms in chronic disease.

ACUTE MESENTERIC ISCHEMIA (AMI)

Etiology & Relative Frequency

Cause

Approx. %

Arterial embolism (SMA)

40–50%

Arterial thrombosis

20–30%

NOMI

20–30%

Mesenteric venous thrombosis

5–10%


1. Arterial Embolic AMI

Pathophysiology

  • Embolus lodges in proximal SMA
  • Jejunum & ileum affected
  • Colon often spared initially

Risk Factors

  • Atrial fibrillation (most common)
  • Recent MI
  • Valvular heart disease
  • Dilated cardiomyopathy

Clinical Hallmark

“Pain out of proportion to physical findings”

  • Sudden, severe abdominal pain
  • Minimal tenderness initially
  • Vomiting, diarrhea → later bloody stools


2. Arterial Thrombotic AMI

Pathophysiology

  • Thrombosis on pre-existing atherosclerotic SMA
  • Often near vessel origin

Clues

  • History of chronic mesenteric ischemia
  • Gradual worsening pain
  • Severe metabolic derangement at presentation

Prognosis

  • Worse than embolic AMI (poor collaterals)


3. Non-Occlusive Mesenteric Ischemia (NOMI)

Mechanism

  • Severe splanchnic vasoconstriction
  • Reduced cardiac output or hypotension
  • No mechanical obstruction

Triggers

  • Septic shock
  • Cardiogenic shock
  • High-dose vasopressors (noradrenaline)
  • Post-cardiac surgery
  • Hemodialysis, burns

Key Point

Abdominal pain may be absent or masked in ventilated/sedated patients

Mortality

  • Up to 70–90%


4. Mesenteric Venous Thrombosis (MVT)

Pathophysiology

  • Venous congestion → bowel wall edema → ischemia

Risk Factors

  • Hypercoagulable states
  • Cirrhosis, portal hypertension
  • Malignancy
  • Pancreatitis
  • Oral contraceptives

Presentation

  • Subacute pain (days)
  • Less severe initially
  • Ascites common


CHRONIC MESENTERIC ISCHEMIA (CMI)

Classic Triad 

  1. Post-prandial abdominal pain
  2. Fear of eating
  3. Weight loss

Cause

  • Atherosclerosis involving ≥2 mesenteric vessels

Pain Timing

  • 15–60 min after meals
  • Lasts 1–3 hours


PATHOPHYSIOLOGY OF BOWEL INJURY

  1. Hypoperfusion → mucosal hypoxia
  2. Loss of epithelial barrier
  3. Bacterial translocation
  4. Lactic acidosis
  5. Transmural necrosis
  6. Perforation → sepsis → MODS


CLINICAL FEATURES (Stage-wise)

Early

  • Severe abdominal pain
  • Soft abdomen
  • Normal bowel sounds

Intermediate

  • Guarding
  • Bloody diarrhea
  • Ileus

Late

  • Peritonitis
  • Shock
  • Multi-organ failure


LABORATORY FINDINGS (Late & Non-Specific)

  • Metabolic acidosis
  • High serum lactate (late marker)
  • Leukocytosis
  • Elevated D-dimer
  • Hemoconcentration

Normal lactate does NOT exclude mesenteric ischemia


IMAGING – GOLD STANDARD

CT Angiography (CTA)

Investigation of choice

Findings:

  • SMA occlusion / narrowing
  • Bowel wall thickening or thinning
  • Pneumatosis intestinalis
  • Portal venous gas
  • Reduced bowel wall enhancement

Other Modalities

  • Plain X-ray: late signs only
  • Doppler US: limited utility
  • Conventional angiography: therapeutic role (NOMI)


MANAGEMENT (Time = Bowel)

Initial ICU Management (All Patients)

  • High-flow oxygen
  • Aggressive IV fluids
  • Broad-spectrum antibiotics
  • Nasogastric decompression
  • Avoid vasoconstrictors if possible
  • Correct acidosis & electrolytes


Etiology-Specific Treatment

Arterial Embolism

  • Immediate embolectomy
  • Endovascular thrombectomy (selected cases)

Arterial Thrombosis

  • Surgical revascularization
  • Bypass or endarterectomy

NOMI

  • Treat underlying shock
  • Reduce vasopressors
  • Intra-arterial papaverine infusion

Mesenteric Venous Thrombosis

  • Anticoagulation is primary therapy
  • Surgery only if peritonitis/infarction


SURGICAL INDICATIONS

  • Peritonitis
  • Bowel perforation
  • Transmural infarction
  • Persistent acidosis despite resuscitation

Second-look laparotomy often required at 24–48 hours.


PROGNOSIS

Factor

Outcome

Early diagnosis

Improved survival

NOMI

Worst prognosis

Delayed surgery

High mortality

Elevated lactate

Late, poor outcome


EXAM- PEARLS 

  • Pain out of proportion = think SMA embolism
  • ICU patient + vasopressors + ileus = NOMI
  • CTA is diagnostic test of choice
  • Normal lactate does not rule out ischemia
  • MVT → anticoagulation, not immediate surgery



ONE-LINE SUMMARY

Mesenteric ischemia is a vascular catastrophe where early suspicion, rapid CTA, and timely revascularization are the only determinants of survival.