Obstruction & Pseudo-obstruction

Large Bowel Obstruction (LBO)

Definition

• Large bowel obstruction: Obstruction distal to the ileocecal valve affecting the colon.

Classification

Mechanical (Dynamic) Obstruction

• Intraluminal causes:
  • Intrinsic mass (e.g., colorectal cancer)
  • Foreign bodies
    • Bezoars
    • Fecal impaction
• Mural causes:
  • Diverticular strictures
  • Crohn's disease strictures
  • Ischemic strictures
  • Radiation strictures
  • Infectious strictures (e.g., tuberculosis)
  • Hirschsprung disease
• Extraluminal causes:
  • Sigmoid volvulus
  • Cecal volvulus
  • Hernias (inguinal, ventral, internal)
  • Metastatic/intra-abdominal tumors
  • Abdominal abscesses
  • Retroperitoneal fibrosis
  • Adhesions (rare in large bowel)

Functional (Adynamic or Pseudo-obstruction)

• Colonic pseudo-obstruction (Ogilvie syndrome)
• Toxic megacolon
• Paralytic ileus

Common Etiologies

• United States: Most common cause is colorectal cancer (CRC).
• Worldwide: Colonic volvulus is responsible for ~1/3 of LBO cases.
  • Sigmoid volvulus is the most common type.
  • Cecal volvulus also occurs.

Pathophysiology

• Distention:
  • Accumulation of gas (swallowed air and bacterial fermentation) and stool proximal to obstruction.
• Ischemia and Perforation:
  • Increased intraluminal pressure can exceed capillary pressure, leading to ischemic necrosis.
  • Closed-loop obstructions (e.g., volvulus, strangulated hernias) have higher risk due to trapped segments.
  • Law of Laplace: The cecum is prone to perforation due to its largest diameter and wall stress under pressure.

Clinical Presentation

• Mechanical Obstruction:
  • Acute obstruction: Rapid onset of pain, distension, abdominal tenderness.
  • Progressive obstruction: Increasing constipation, pencil-thin stools, intermittent abdominal pain.
  • Symptoms:
    • Increased peristalsis with low-grade colicky pain.
    • Failure to pass stool and flatus.
    • Abdominal distention.
    • Bowel sounds: May be increased initially, decreased in late obstruction.
• Functional Obstruction:
  • Distension, vague abdominal pain.
  • Weak or absent bowel sounds.

Diagnosis and Assessment

• History and Physical Examination:
  • Onset and progression of symptoms.
  • Background illnesses and medications.
  • Abdominal examination: Masses, tenderness, previous incisions.
  • Groin examination: Look for hernias.
  • Digital rectal examination: Check for neoplasms and fecal impaction.
• Imaging Studies:
  • Plain abdominal films:
    • Localize obstruction.
    • Assess degree of distension.
    • Determine competency of ileocecal valve.
    • Sigmoid volvulus: "Bent inner-tube" appearance.
  • CT Scan:
    • Enhanced with water-soluble and IV contrast.
    • Identifies location and etiology (e.g., diverticulitis, IBD).
    • Detects signs of ischemia and perforation.
    • Volvulus: Characteristic mesenteric whorl.
• Laboratory Tests:
  • Electrolyte abnormalities.
  • Increased WBC count, CRP.
  • Lactate levels, base excess, pH: Indicators of severity.
• Endoscopy:
  • Assists in diagnosis and allows for biopsies.
  • Therapeutic uses:
    • Detorsion of volvulus.
    • Stent placement in malignant or benign obstructions.

Treatment

• General Principles:
  • Prompt relief of mechanical obstructions to prevent ischemia and perforation.
  • Immediate surgery for patients with peritonitis, signs of perforation, or ischemic bowel.
• Specific Treatments:
  • Sigmoid Volvulus:
    • Endoscopic decompression with rectal tube placement.
    • If unsuccessful or in recurrent cases, elective sigmoid resection with primary anastomosis.
  • Cecal Volvulus:
    • Primary resection with anastomosis (if patient condition allows).
  • Obstructing Colon Cancers:
    • Left-sided obstructions:
      • Endoscopic stenting as bridge to surgery or initial surgery.
      • Surgical options:
        • Segmental resection with Hartmann procedure.
        • Primary anastomosis with or without diverting stoma.
      • Subtotal colectomy if cecum is nonviable.
    • Right-sided obstructions:
      • Right hemicolectomy with primary anastomosis.
      • Consider diverting stoma if high risk for anastomotic failure.
  • Inflammatory Bowel Disease (IBD):
    • May respond to steroids.
    • Paracolic abscesses can be drained percutaneously.
  • Foreign Bodies:
    • Removal via endoscopy.
  • Fecal Impaction:
    • Stool softeners, laxatives.
    • Manual disimpaction under anesthesia if necessary.
  • Hernias:
    • Typically require surgical repair.
  • Intussusception in Adults:
    • Often associated with a pathologic lead point (e.g., polyp, cancer).
    • Requires surgical resection following oncologic principles.

Colonic Pseudo-obstruction (Ogilvie Syndrome)

Definition

• Acute colonic pseudo-obstruction: Acute dilatation of the colon without mechanical obstruction.

Pathophysiology

• Dysregulation of colonic autonomic innervation.
• Possible mechanisms:
  • Autonomic imbalance: Excess sympathetic over parasympathetic activity.
  • Disrupted colonic reflex arcs.
  • Influence of chronic diseases and medications.

Risk Factors and Associated Conditions

• Common in elderly and comorbid patients.
• Often occurs postoperatively or following acute illness.
• Associated Conditions:
  • Postsurgical: Orthopedic/spinal surgery, organ transplants, cardiac procedures.
  • Neurologic diseases: Parkinson's disease, Alzheimer's disease, stroke.
  • Cardiac: Congestive heart failure, myocardial infarction.
  • Pulmonary: Chronic obstructive pulmonary disease (COPD).
  • Trauma: Major trauma, burns, shock.
  • Metabolic: Diabetes mellitus, renal failure, electrolyte disturbances.
  • Infections: Cytomegalovirus, varicella-zoster virus.
  • Obstetric/Gynecologic: Cesarean section, childbirth.
  • Medications: Opiates, anticholinergics, chemotherapy agents.

Clinical Presentation

• Symptoms:
  • Abdominal distension and pain.
  • Nausea and vomiting.
  • Obstipation (severe constipation).
  • Diarrhea may occur due to hypersecretion.
• Physical Examination:
  • Decreased or absent bowel sounds.
  • High-pitched, tinkling sounds may be present.
  • Lack of systemic toxicity or peritoneal signs unless ischemia/perforation occurs.

Diagnosis

• Imaging Studies:
  • Plain abdominal radiographs:
    • Dilated colon, especially cecum and right colon (diameter up to 10-12 cm).
    • Gas present down to distal rectum.
  • CT Scan:
    • Confirms absence of mechanical obstruction.
    • Assesses for ischemia or perforation.
• Differential Diagnosis:
  • Mechanical obstruction.
  • Toxic megacolon due to Clostridioides difficile or other causes.

Management

Supportive Care

• Initial treatment for cecal diameter <12 cm without ischemia/perforation.
• Interventions:
  • NPO (nothing by mouth).
  • Correct electrolyte imbalances.
  • Discontinue contributing medications (e.g., opiates).
  • Nasogastric and rectal tubes for decompression.
  • Encourage ambulation and positional changes.

Pharmacologic Therapy

• Neostigmine:
  • Acetylcholinesterase inhibitor enhancing colonic motility.
  • Dosage: 2-2.5 mg IV over 3-5 minutes.
  • Contraindications: Mechanical obstruction, ischemia, perforation.
  • Side effects: Bradycardia, salivation, cramps.
  • Requires monitoring with atropine available.

Endoscopic Decompression

• Indicated if neostigmine is contraindicated or ineffective.
• Colonoscopy to decompress colon and place a decompression tube.
• Success rates: 61%-95% for initial decompression.
• Perforation risk: 1%-3%.

Surgical Options

• For patients unresponsive to other treatments or with signs of ischemia/perforation.
• Procedures:
  • Tube cecostomy or cecostomy if colon is viable.
  • Resection with diverting stoma if ischemia or perforation is present.

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Note: Early recognition and appropriate management of both large bowel obstruction and colonic pseudo-obstruction are crucial to prevent serious complications such as ischemia and perforation.