Pocket Pediatrics: The Massachusetts General Hospital for Children Handbook of Pediatrics (Pocket Notebook Series), 2 Ed.

HYPERAMMONEMIA

Definition (Pediatrics 1998;192:E69; Vademecum Metabolicum 2004:8)

• Suspect metabolic dz in neonate if NH₃ >200 μmol/L; all other ages NH₃ >100 μmol/L

Ddx: Always consider medication effect

• Urea cycle defects (no acidosis) and organic acidemias (+ metabolic acidosis), liver failure

• Neonates can have transient hyperammonemia of the newborn → sx w/i 24 hr of birth; large premature infants with pulm dz. Usually no recurrent hyperammonemia

Labs

Labs as above; must have uncuffed venous or arterial sample, on ice, sent stat

• AA in plasma and urine, organic acids and orotic acid in urine

• Acylcarnitine in dried blood spots

Treatment

• Must contact metabolic team immediately

• NH₃ >500 → central line, art line, HD

• 1st infusion: 12 cc/kg D10 over 2 hr with lytes

• Arginine hydrochloride 360 mg/kg

• Na-benzoate 250 mg/kg (alternate pathway for nitrogen excretion)

• Carnitine 100 mg/kg

• Ondansetron 0.15 mg/kg IV bolus in noncomatose (to prevent N/V)

• Follow glucose, add insulin if needed, check ammonia after 2 hr

• Ref: Neonate: http://newenglandconsortium.org/for-professionals/acute-illness-protocols/urea-cycle-disorders/neonate-with-hyperammonemia/

• Infant/child: http://newenglandconsortium.org/for-professionals/acute-illness-protocols/urea-cycle-disorders/infantchild-with-hyperammonemia/