Colonic Blood Supply – Why the Colon Is Vulnerable

Major Arteries

• Superior Mesenteric Artery (SMA) – proximal colon
• Inferior Mesenteric Artery (IMA) – distal colon
• Internal iliac arteries – rectum

Watershed (Border-Zone) Areas

These regions have poor collateral flow and are most susceptible:

1. Splenic flexure (SMA–IMA junction) – most common
2. Rectosigmoid junction (IMA–hypogastric junction)

Pathophysiology

Primary Mechanisms

1. Hypoperfusion (most common)
• ↓ Cardiac output
• Hypotension / shock
• Dehydration
• Sepsis

2. Vascular obstruction

• Atherosclerosis
• Embolism (rare vs small bowel ischemia)
• Venous thrombosis

3. Vasoconstriction

• Vasopressors (noradrenaline)
• Cocaine, ergot alkaloids, digoxin

Cellular Events

• Mucosal hypoxia → ATP depletion
• Increased permeability → bacterial translocation
• Reperfusion → oxidative stress
• Progression: mucosal → mural → transmural necrosis

Risk Factors

Cardiovascular

• Atrial fibrillation
• Congestive heart failure
• Recent MI
• Peripheral vascular disease

Systemic / ICU-Related

• Septic shock
• Prolonged hypotension
• Vasopressor therapy
• Hemodialysis
• Major surgery (especially aortic / cardiac)

Drugs

• NSAIDs
• Oral contraceptives
• Vasoconstrictors
• Chemotherapy agents

Clinical Presentation

Typical Triad

1. Sudden crampy abdominal pain (often left-sided)
2. Urgent desire to defecate
3. Hematochezia or bloody diarrhea (within 24 h)

Other Features

• Mild–moderate tenderness
• Low-grade fever
• Nausea, vomiting
• Usually not severe peritonitis unless transmural infarction

Key exam point: Pain is out of proportion less dramatic than acute mesenteric ischemia.

Severity Classification

Investigations

Laboratory Findings

• Leukocytosis
• Elevated CRP
• Metabolic acidosis (severe cases)
• Lactate: normal or mildly elevated (unlike AMI)

Labs are non-specific — diagnosis is imaging + endoscopy based.

Imaging

CT Abdomen with Contrast (Investigation of Choice)

CT Features

• Segmental colonic wall thickening
• Thumbprinting (submucosal edema/hemorrhage)
• Pericolonic fat stranding
• Reduced mural enhancement
• Pneumatosis coli (severe)
• Portal venous gas (ominous)

Colonoscopy (Gold Standard for Diagnosis)

Typical Findings

• Pale, edematous mucosa
• Petechial hemorrhages
• Cyanosis
• Longitudinal ulcers
• Sharp demarcation between normal & affected bowel

Avoid colonoscopy if peritonitis or suspected perforation

Histopathology

• Mucosal & submucosal hemorrhage
• Withered crypts
• Lamina propria hyalinization
• Minimal inflammation (helps differentiate from IBD)

Differential Diagnosis

Management

Initial Conservative Management (Most Patients)

• Bowel rest (NPO)
• IV fluids (optimize perfusion)
• Oxygen
• Broad-spectrum antibiotics
  (Gram-negative + anaerobic coverage)
• Stop vasoconstrictive drugs if possible

80–85% recover with conservative treatment

Indications for Surgery

• Peritonitis
• Bowel perforation
• Gangrene
• Persistent bleeding
• Failure of conservative therapy
• Toxic megacolon

Surgical Options

• Segmental colectomy
• Hartmann’s procedure (critically ill)
• Damage-control surgery in ICU patients

Prognosis

• Mild disease: excellent recovery
• Severe/gangrenous disease: mortality 40–60%
• Poor prognostic factors:
• Right-sided involvement
• Hypotension
• Renal failure
• High lactate
• ICU admission

Special ICU Perspective

• Often under-diagnosed in septic shock
• May present with ileus + unexplained metabolic acidosis
• Vasopressors worsen splanchnic ischemia
• Early CT and low threshold for surgical consult are critical