Ornithine transcarbamylase deficiency, citrullinemia, methylmalonic acidemia, tyrosinemia, phenylketonuria, Galactosemia… did I lose you yet? These words bring me back to the dark place of step one studying. So take a deep breath, don’t worry about the big words and here are a couple of tips next time you have a “metabolic kid” in the peds ED.

Four Tests to Rember:

  • Lactate — can indicate metabolic crisis
  • Respiratory alkalosis — suggests an exogenous drive for hyperpnea, that can be caused by toxic levels ammonia which directly stimulate the respiratory center
  • UA for ketones — high when in metabolic crisis or absence in the setting of hypoglycemia
  • Ammonia — greater than 200 = yikesville!

Manifestations of metabolic crisis:

  • Neurologic: irritability/lethargy, vomiting, hypotonia, seizures. 
  • Tachypnea from metabolic acidosis and hyperventilation from hyperammonia
  • Vomiting

Comprehensive diagnostic testing options:

  • Venous blood gas
  • Blood sugar
  • Comprehensive metabolic panel
  • Clotting studies
  • Ammonia level (heparinized tube on ice)
  • Urinalysis
  • Plasma amino acids (heparinized tube on dry ice)
  • Urine organic acids, orotic acids, and amino acids (on ice)
  • Plasma-free and acylcarnitines (heparinized tube)
  • Urine-reducing substances (on ice)

Treatment

  • Provide energy while shutting down catabolism
    • hypoglycemia can cause irreversible neurologic damage
  • Correcting electrolyte and/or acid base imbalances
  • Remove toxic metabolites
    • sodium benzoate, sodium phenylacetate (Ammonul), arginine hydrochloride –> ammonia elimination in the urine
    • if ammonia >500 –> hemodialysis

References:

MacNeill, EC et al. Inborn Errors of Metabolism in the Emergency Department (Undiagnosed and Management of the Known) Emergency Medicine Clinics of North America, 2018-05-01, Volume 36, Issue 2, Pages 369-385.