Threshold for toxicity from hyperammonemia in critically ill children

Area of Science:

• Pediatric critical care
• Metabolic disorders
• Toxicology

Background:

• Hyperammonemia, caused by reduced liver function or urea cycle enzyme deficiency, can lead to severe cerebral edema and herniation.
• The precise ammonia toxicity threshold and its impact on pediatric mortality remain incompletely understood.

Purpose of the Study:

• To determine the ammonia toxicity threshold associated with mortality in critically ill children.
• To identify risk factors for mortality in pediatric hyperammonemia.
• To compare treatment patterns and outcomes between liver failure and urea cycle defects.

Main Methods:

• Retrospective observational study of pediatric intensive care unit patients with hyperammonemia (January 2000 - April 2009).
• Data collected included clinical and laboratory parameters, treatments, and ammonia levels within the first 7 days.
• Logistic regression analysis was used to estimate the risk of 28-day mortality.

Main Results:

• Ninety patients were included, primarily with liver failure (63.3%) or urea cycle defects (23.3%).
• A 28-day mortality rate of 31.1% was observed.
• Ammonemia ≥200 μmol/L within 48 hours was an independent risk factor for mortality (OR 3.3), with higher risk in liver failure compared to urea cycle defects. Ammonia scavengers were less frequently used in liver failure.

Conclusions:

• An ammonia threshold of ≥200 μmol/L within 48 hours significantly increases mortality risk in pediatric hyperammonemia, particularly in cases of liver failure.
• Timely and appropriate use of ammonia scavengers may be crucial, as they were underutilized in liver failure patients despite potential benefits.