Hyperammonemia

Background

Pathophysiology

• Acquired: liver failure results in shunting of blood from the liver to the inferior vena cava, decreased filtration of blood and removal of nitrogen-containing toxins by the liver, and then hyperammonemia.
• Congenital: Defect in one of the enzymes of the urea cycle, which leads to lower production of urea from ammonia.

Types

• Primary
  • Caused by several inborn errors of metabolism
  • Characterized by reduced activity of urea cycle enzymes
• Secondary
  • Caused by inborn errors of intermediary metabolism (i.e. reduced activity of enzymes that are not part of the urea cycle)
    • Normally from acute or chronic liver failure

Evaluation

Acquired vs. Congenital

• Acquired
  • Diseases that result in liver failure
  • Medications (e.g. valproic acid overdose)
  • Severe dehydration (from small intestinal bacterial overgrowth)
  • Glycine toxicity (CNS symptoms and nausea)
• Congenital
  • Genetic

Management

• Treat underlying disorder

Disposition

• Depends on cause

See Also

• Inborn errors of metabolism
• Hepatic encephalopathy