What are the causes of hyperammonemia in the setting of severe Acute Kidney Injury (AKI) and normal liver enzyme levels?

From the Guidelines

Elevated ammonia levels in severe acute kidney injury (AKI) with normal liver enzymes primarily result from impaired renal clearance of ammonia, as the kidneys are unable to effectively convert ammonia to urea or excrete it directly 1. In the setting of severe AKI, the kidneys play a crucial role in ammonia clearance, and their dysfunction leads to ammonia accumulation. Key factors contributing to hyperammonemia in this context include:

• Impaired renal ammonia clearance
• Increased ammonia production due to metabolic stress and tissue breakdown
• Potential intestinal ammonia production and absorption Management strategies should focus on addressing the underlying AKI, reducing ammonia production, and enhancing its clearance. Some approaches include:
• Supportive care and fluid management to optimize renal function
• Renal replacement therapy, such as hemodialysis or continuous renal replacement therapy (CRRT), to remove ammonia
• Dietary protein restriction to 0.6-0.8 g/kg/day to minimize ammonia production
• Use of lactulose or rifaximin to reduce intestinal ammonia production and absorption
• Correction of metabolic acidosis with sodium bicarbonate to decrease ammonia production
• Consideration of L-carnitine supplementation to enhance ammonia metabolism It is essential to identify and address any contributing factors, such as urinary tract infections, certain medications, or gastrointestinal bleeding, which can exacerbate ammonia production. By prioritizing these strategies, clinicians can effectively manage hyperammonemia in patients with severe AKI and normal liver enzymes, ultimately reducing the risk of neurological impairment and improving patient outcomes 1.

From the Research

Causes of Hyperammonemia in Severe Acute Kidney Injury (AKI)

• Hyperammonemia can be caused by various factors, including valproic acid concentrations 2, 3, 4
• Valproic acid, a branched short-chain fatty acid, can induce carnitine depletion, resulting in high levels of ammonia in blood 2
• Dehydration-associated pseudo-hyperammonemia can also cause altered mental status, and may be treated with intravascular resuscitation instead of lactulose 5
• In the setting of severe AKI, hyperammonemia may be caused by factors such as:
  • Medications like valproic acid 2, 3, 4
  • Dehydration 5
  • Other less common etiologies, although the provided studies do not directly address these causes in the context of AKI with normal liver enzyme levels

Treatment and Management

• Treatment of valproic acid-induced hyperammonemia may involve discontinuation of valproic acid, lactulose, or levocarnitine therapy 3, 4
• The effectiveness of different treatment modalities, such as lactulose, levocarnitine, and combination therapy, has been compared in critically ill patients 4
• In some cases, hyperammonemia may resolve with fluid bolus and maintenance fluid without requiring lactulose or rifaximin 5