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.
