Special Surgery 26. Acute and Chronic Intestinal Ischemia

I. Basic Concepts and Vascular Anatomy

Definition

• Intestinal ischemia: insufficient blood supply to small bowel and/or colon
• Acute intestinal ischemia: sudden perfusion failure → bowel ischemia, infarction, perforation risk
• Chronic intestinal ischemia / intestinal angina: recurrent postprandial ischemia from arterial stenosis
• Most dangerous acute form: acute mesenteric ischemia, usually SMA territory

Blood Supply and Risk Zones

• Celiac trunk: foregut
• SMA: midgut → distal duodenum to proximal 2/3 transverse colon; key vessel in AMI
• IMA: hindgut → distal transverse colon to upper rectum
• Collaterals:

• Pancreaticoduodenal arcades
• Marginal artery of Drummond
• Arc of Riolan

• Watershed areas: splenic flexure, rectosigmoid junction → vulnerable in low-flow states

II. Acute Intestinal Ischemia

Definition and Causes

• Sudden interruption or severe reduction of intestinal blood flow
• Progression: mucosal injury → transmural infarction → perforation/peritonitis if untreated
• Arterial embolism: atrial fibrillation, recent MI, valvular disease, endocarditis
• Arterial thrombosis: atherosclerotic stenosis, often proximal SMA
• May have previous chronic intestinal angina
• Non-occlusive mesenteric ischemia (NOMI): low-flow state without fixed occlusion

• Shock, heart failure, sepsis, ICU state, hemodialysis hypotension, high-dose vasopressors

• Mesenteric venous thrombosis: hypercoagulable state, malignancy, portal hypertension/cirrhosis
• Other venous causes: pancreatitis/infection, pregnancy/postpartum, recent surgery

Clinical Features

• Classic early sign: severe abdominal pain out of proportion to physical findings
• Early abdomen can be soft despite severe pain
• Nausea, vomiting, diarrhea, urgent defecation
• Hematochezia / blood in stool if mucosal sloughing occurs
• Later: abdominal distension, ileus, peritonitis
• Peritonitis = bowel infarction/perforation until proven otherwise
• Late signs: fever, tachycardia, hypotension, shock, sepsis

Diagnosis

• CT angiography abdomen/pelvis: diagnostic test of choice
• Do not delay CTA because of mild renal dysfunction if AMI is strongly suspected
• CTA vascular findings:

• Arterial embolus/thrombosis
• Venous thrombosis

• CTA bowel findings:

• Poor wall enhancement, dilatation, edema, ascites
• Pneumatosis, portal venous gas, free air

• Labs: leukocytosis, high CRP, acidosis, lactate ↑, renal dysfunction
• Lactate is a severity marker but can be late; normal lactate does not exclude early ischemia
• Plain X-ray: low sensitivity; late signs include ileus, air-fluid levels, pneumatosis or free air

Treatment

1. Immediate General Treatment

• Urgent surgical + vascular/interventional radiology consultation
• NPO, large-bore IV access, fluid resuscitation
• Oxygen / ICU monitoring if severe
• Correct shock, acidosis, electrolytes and organ hypoperfusion
• NG tube if ileus/vomiting
• Broad-spectrum IV antibiotics: Gram-negative + anaerobic coverage
• Systemic unfractionated heparin unless contraindicated

2. Revascularization and Surgery

• Peritonitis, perforation or obvious necrosis → emergency laparotomy
• Resect clearly necrotic bowel; preserve borderline bowel if possible
• Second-look operation after 24-48 h if bowel viability is uncertain
• Arterial embolism: embolectomy or endovascular therapy
• Arterial thrombosis: stent/angioplasty or open bypass/endarterectomy
• Venous thrombosis without peritonitis: anticoagulation first
• Surgery if infarction or peritonitis
• NOMI: treat low-flow cause, improve perfusion, reduce vasopressors

III. Ischemic Colitis: High-Yield Note

Key Points

• Ischemic colitis: hypoperfusion injury of colon, often left-sided/watershed related
• Symptoms: crampy abdominal pain, urgent defecation, bloody diarrhea/hematochezia
• Mild/moderate cases:

• Bowel rest, IV fluids, correct hypotension
• Stop vasoconstrictive drugs
• Antibiotics if moderate/severe/systemic signs

• Surgery if peritonitis, perforation, gangrenous colon, uncontrolled sepsis, massive bleeding or deterioration

IV. Chronic Intestinal Ischemia

Definition and Causes

• Chronic mesenteric ischemia / intestinal angina: recurrent intestinal ischemia after meals
• Cause: progressive mesenteric arterial narrowing, usually atherosclerosis
• Often involves at least two major arteries: celiac trunk, SMA, IMA
• Risk factors: smoking, diabetes, hypertension, dyslipidemia, coronary/peripheral/cerebrovascular disease

Clinical Features

• Postprandial abdominal pain: starts 15-60 min after eating, lasts 1-3 h
• Food fear / sitophobia
• Weight loss due to reduced intake
• Nausea, bloating, diarrhea or constipation
• Abdominal bruit may be present but is not reliable
• Acute-on-chronic thrombosis can present as acute mesenteric ischemia

Diagnosis

• Diagnosis: symptoms + significant mesenteric arterial stenosis
• Exclude other causes of abdominal pain/weight loss
• Imaging:

• CT angiography: first-line anatomic test in many centers
• MR angiography: alternative if CT contrast/radiation is problematic
• Duplex ultrasound: screening/follow-up; increased flow velocity suggests stenosis

Treatment

• Risk factor control:

• Smoking cessation, statin, antiplatelet therapy
• Control diabetes, blood pressure and lipids

• Nutritional support if significant weight loss
• Symptomatic chronic intestinal ischemia usually needs revascularization
• Goal: restore postprandial intestinal perfusion and prevent acute thrombosis
• Endovascular angioplasty/stenting: first-line in most patients
• Open bypass/endarterectomy: selected young/low-risk patients or failed stent