Can ileus cause elevated ammonia levels?

Ileus Can Cause Elevated Ammonia Levels

Yes, ileus can cause elevated ammonia levels in the blood (hyperammonemia). This relationship is supported by clinical evidence and is an important consideration in the management of patients with ileus, particularly those with underlying liver disease.

Mechanism of Ileus-Induced Hyperammonemia

• Intestinal stasis: Ileus causes decreased intestinal motility, leading to stasis of intestinal contents 1
• Bacterial overgrowth: Prolonged intestinal stasis promotes bacterial overgrowth in the small intestine 2
• Ammonia production: Intestinal bacteria produce ammonia through:
  • Bacterial hydrolysis of urea
  • Bacterial protein deamination 2
• Increased absorption: Ammonia is absorbed from the intestinal lumen into the bloodstream, particularly in the ileum 3
• Impaired clearance: In patients with compromised liver function, the ability to convert ammonia to urea is reduced, exacerbating hyperammonemia 4

Clinical Significance

Hyperammonemia is clinically significant because:

• Normal ammonia levels are ≤35 µmol/L (<60 µg/dL) 5
• Levels >200 µmol/L (341 µg/dL) are associated with poor neurological outcomes 5
• Elevated ammonia can lead to neurological symptoms including:
  • Lethargy
  • Loss of appetite
  • Vomiting
  • Hyperventilation
  • Hypotonia
  • Ataxia
  • Disorientation
  • Seizures
  • Coma and death if untreated 5

Management Approach for Ileus-Associated Hyperammonemia

1. Treat the underlying ileus:

   • Correct electrolyte imbalances
   • Address underlying causes
   • Consider prokinetic agents when appropriate

2. Reduce ammonia production:

   • Non-absorbable disaccharides (first-line treatment):

     • Lactulose (30-45 mL every 1-2 hours initially, then titrate to 2-3 soft stools per day) 6
     • Lactitol (67-100 g daily equivalent) 6
     • For severe cases or patients unable to take oral medications: lactulose enema (300 mL lactulose + 700 mL water, 3-4 times daily) 6

   • Non-absorbable antibiotics:

     • Rifaximin (shown to have positive effects in managing hyperammonemia) 6
     • Combination therapy with lactulose and rifaximin shows better recovery rates (76% vs. 44%) 6

3. For severe hyperammonemia:

   • Consider continuous kidney replacement therapy (CKRT) 5

Special Considerations

• Patients with liver disease: More susceptible to developing hyperammonemia with ileus due to already compromised ammonia metabolism 4
• Post-hepatectomy patients: Particularly vulnerable to ileus-induced hyperammonemia; proactive management with agents like Dai-kenchu-to has shown benefit in reducing postoperative ammonia levels 1
• Monitoring: Regular assessment of ammonia levels and neurological status is essential in patients with ileus, especially those with risk factors for hyperammonemia

Common Pitfalls to Avoid

• Delayed recognition: Failure to consider hyperammonemia in patients with ileus who develop neurological symptoms
• Inadequate treatment: Insufficient dosing of lactulose or failure to escalate to combination therapy when needed
• Overlooking other causes: Not considering other potential causes of hyperammonemia (urea cycle disorders, medications, etc.)
• Neglecting the underlying cause: Focusing only on ammonia reduction without addressing the ileus itself

Constipation and ileus are recognized precipitating factors for hepatic encephalopathy, with ammonia being the key mediator of neurological symptoms 6. Early recognition and aggressive management of ileus can prevent the development of significant hyperammonemia and its associated neurological complications.