Mesenteric ischemia

Background

Frontal view of the superior mesenteric artery and its branches. The large vessel (blue) beside the SMA is the superior mesenteric vein. A considerable number of different branching patterns exist.

Colonic blood supply. Pink - supply from superior mesenteric artery (SMA) and its branches: middle colic, right colic, ileocolic arteries. Blue - supply from inferior mesenteric artery (IMA) and its branches: left colic, sigmoid, superior rectal artery. 7 is for so-called Cannon-Böhm point (the border between the areas of SMA and IMA supplies), which lies at the splenic flexure.

• Most commonly superior mesenteric artery (SMA), thus typically involves small bowel (especially jejunum) and right colon
• Left colon uncommonly involved due to collateral flow
• Mean age = 70 years old (>70% of cases occur in women)

Pathophysiology

4 distinct entities:

1. Mesenteric arterial embolism (ex. Afib)
2. Mesenteric arterial thrombosis (ex. Vasculopath)
3. Nonocclusive mesenteric ischemia (ex. Hypovolemia from diuretics)
4. Mesenteric venous thrombosis (ex. hypercoagulable state)

Intestinal Ischemic Disorder Types

• Ischemic colitis
  • Accounts for 80-85% of intestinal ischemia
  • Due to non-occlusive disease with decreased blood flow to the colon.
  • Causes decreased perfusion leading to sub-mucosal or mucosal ischemia only.
  • Typical to the "watershed areas" of the colon (Splenic flexure or Sigmoid)

• Acute mesenteric ischemia
  • Due to complete occlusion of mesenteric vessels
  • Complete transmural ischemia

• Mesenteric venous thrombosis
• Chronic mesenteric ischemia ("intestinal angina")

Risk Factors

Risk Factors by Mesenteric Ischemia Type

Type	Risk Factor
Arterial Embolism	Dysrhythmia (A. Fib) Cardiomyopathy Valve Disease Endocarditis MI
Arterial Thrombosis	Atherosclerotic Disease
Venous Thrombosis	Prior thrombosis history Hypercoagulable state (pregnancy, cancer, clotting disorder)
Nonocculsive	Hypovolemic state Heart failure Myocardial infarction with decrease output Sepsis Diuretic use

Clinical Features

• Pain out of proportion to exam
  • Abdomen often soft, without guarding.
  • Pain often left sided around watershed areas of colon (splenic flexure and recto-sigmoid junction)
  • Severe, generalized, colicky
• Bloody stools

Differential Diagnosis

Colitis

• Infectious colitis
• Ischemic colitis
• Ulcerative colitis
• CMV colitis
• Crohn's colitis
• Toxic colitis (antineoplastic agents)
• Pseudomembranous colitis
• Fibrosing colonopathy (Cystic fibrosis)

Diffuse Abdominal pain

• Abdominal aortic aneurysm
  • Aortocaval fistula
• Acute gastroenteritis
• Aortoenteric fisulta
• Appendicitis (early)
• Bowel obstruction
  • Large bowel obstruction
    • Ogilvie's syndrome
  • Small bowel obstruction
  • Malignant bowel obstruction
• Bowel perforation
• Diabetic ketoacidosis
• Gastroparesis
• Hernia
• Hypercalcemia
• Inflammatory bowel disease
• Mesenteric ischemia
  • Mesenteric vein thrombosis
• Pancreatitis
• Peritonitis
• Sickle cell crisis
• Spontaneous bacterial peritonitis
• Volvulus

Evaluation

CT showing dilated loops of small bowel with thickened walls (black arrow), findings characteristic of ischemic bowel due to thrombosis of the superior mesenteric vein.

Workup

• Labs
  • CBC
  • Chemistry
  • LFTs
  • Lipase
  • Lactate
  • Consider UA
• CTA abdomen/pelvis (Bowel wall edema is the most common finding on CT)
• Mesenteric angiography considered gold standard (if available, typically as a secondary study)

Diagnosis

• Typically diagnosed on CT
• Labs may show the following (although do not rule need for CT):
  • Lactate (higher later)
  • WBC (often >15K)
  • Chemistry (metabolic acidosis)
  • Hyperphosphatemia

Management

General

• Aggressive IVF resuscitation, continued after revascularization due to capillary leak
  • Correct electrolyte imbalances prior to IV contrast or surgical exploration
• Analgesia (usually Opioids
• IV antibiotics - broad spectrum antibiotics to prevent sepsis
  • Second-generation cephalosporin plus metronidazole, OR
  • Levofloxacin 500 mg IV q24 hours PLUS Metronidazole 15 mg/kg IV LOAD over 1 hour, for severely ill, maintenance 500 mg IV q6 hours, OR
  • Piperacillin/tazobactam 3.375 mg IV q6 hours
• Anticoagulation with heparin is usually appropriate in all patients with mesenteric ischemia, with exception of those with typical contraindications
  • Some experts will recommend delaying heparin for 48 hours due to risk for intraluminal bleeding in bowels

Acute arterial embolus

• Papaverine infusion (30-60m g/h IV) OR
• Surgical embolectomy OR
• Mesenteric artery bypass surgery OR
• Retrograde open mesenteric stenting OR
• tPA intra-arterial thrombolysis with IR
• PLUS/MINUS surgical resection of necrotic bowel after any of above interventions
• PLUS/MINUS 24-48 hour second-look surgery

Nonocclusive mesenteric ischemia

• Transcatheter vasodilation via:
  • PGE1, alprostadil
  • PGI2, epoprostenol
  • Papaverine, most commonly used, though use in caution with angina, recent stroke, MI, glaucoma

Mesenteric venous thrombosis

• Heparin/warfarin either alone or in combination with surgery
• Up to 5% of patients require intervention beyond anticoagulation alone
• Immediate heparinization should be started even when surgical intervention is indicated
  • Decreases progression of thrombosis and improves survival
• PLUS/MINUS tPA intra-arterial thrombolysis with IR
• PLUS/MINUS laparotomy for evidence of bowel necrosis, peritonitis, stricture, severe GI bleeding

Chronic mesenteric ischemia

• Angioplasty with or without stent placement or surgical revascularization

Disposition

• Admit with consultation of one or more of the following:
  • IR
  • Vascular
  • Surgery

See Also

• Abdominal pain