What are the causes of diffuse ileus in the small and large bowel?

Causes of Diffuse Ileus in the Small and Large Bowel

Diffuse ileus affecting both small and large bowel is most commonly caused by postoperative states, intra-abdominal infections, metabolic disturbances, and medications that inhibit intestinal motility.

Primary Causes

1. Postoperative Ileus

• Most common cause following abdominal surgery, particularly colonic procedures 1
• Can occur after non-abdominal surgeries as well
• Duration correlates with degree of surgical trauma
• Pathophysiology involves:
  • Surgical manipulation of bowel
  • Inflammatory mediators
  • Opioid analgesics inhibiting motility
  • Neural reflexes

2. Intra-Abdominal Infections

• Peritonitis from various sources 2:
  • Small bowel perforation (ischemic, inflammatory, infectious, traumatic)
  • Gastroduodenal ulcer perforation
  • Complicated diverticulitis
  • Postoperative peritonitis (anastomotic leak)
• Intra-abdominal abscesses
• Diffuse peritoneal contamination leads to paralytic ileus as a protective mechanism

3. Metabolic and Electrolyte Disorders

• Electrolyte abnormalities 3:
  • Hypokalemia
  • Hypomagnesemia
  • Hypocalcemia
• Uremia
• Diabetic ketoacidosis
• Hypothyroidism
• Severe hyperglycemia

4. Medications

• Opioid analgesics (most common)
• Anticholinergics
• Tricyclic antidepressants
• Calcium channel blockers
• Phenothiazines
• Certain antibiotics (clindamycin)

5. Neurogenic Causes

• Spinal cord injuries
• Retroperitoneal hemorrhage or trauma
• Parkinson's disease
• Multiple sclerosis
• Autonomic neuropathy (diabetic, paraneoplastic)

6. Vascular Causes

• Mesenteric ischemia (arterial or venous)
• Abdominal compartment syndrome 3
• Severe shock states with splanchnic hypoperfusion

7. Systemic Inflammatory Conditions

• Sepsis from any source
• Severe pneumonia
• Severe trauma
• Burns
• Pancreatitis

8. Chronic Intestinal Pseudo-obstruction

• Primary or secondary myopathies 2
• Primary or secondary neuropathies 2
• Mitochondrial disorders (MNGIE)
• Paraneoplastic syndromes (associated with small cell lung cancer, thymoma)
• Connective tissue disorders (scleroderma)

Diagnostic Approach

1. Clinical Presentation:

   • Abdominal distension
   • Nausea and vomiting
   • Absence of bowel sounds
   • Inability to pass flatus or stool

2. Imaging:

   • Plain abdominal radiographs: Dilated small and large bowel loops with air-fluid levels
   • CT scan: Diffusely distended bowel without transition point, helps exclude mechanical obstruction 2

3. Laboratory Tests:

   • Electrolytes (potassium, magnesium, calcium)
   • Thyroid function tests
   • Inflammatory markers
   • Specific antibodies in suspected cases:
     • Anti-neuronal antibodies (paraneoplastic)
     • Scleroderma antibodies (anti-centromere, anti-Sc170)

Management Considerations

1. Supportive Care:

   • Bowel rest
   • Intravenous fluid resuscitation
   • Correction of electrolyte abnormalities
   • Discontinuation of offending medications

2. Specific Treatments:

   • Treatment of underlying infection or inflammation
   • Prokinetic agents
   • Neostigmine for colonic pseudo-obstruction 4
   • Decompressive procedures if severe distension

3. Surgical Intervention:

   • Reserved for cases with:
     • Suspected bowel ischemia
     • Abdominal compartment syndrome
     • Failure of conservative management with progressive distension

Clinical Pearls and Pitfalls

• Pearl: Diffuse ileus affecting both small and large bowel is rarely due to mechanical obstruction and more commonly represents a functional disorder.
• Pitfall: Failing to distinguish between mechanical obstruction and functional ileus can lead to unnecessary surgery or missed opportunity for early intervention.
• Pearl: Persistent ileus beyond 3-5 days should prompt reassessment for underlying complications or missed diagnoses.
• Pitfall: Overlooking electrolyte abnormalities, particularly hypokalemia, which can perpetuate ileus.
• Pearl: In cases of severe distension, consider abdominal compartment syndrome which can lead to multiorgan dysfunction 3.

Remember that diffuse ileus involving both small and large bowel usually indicates a systemic process rather than a focal problem, and management should focus on identifying and treating the underlying cause while providing appropriate supportive care.