What Is Transitory Hyperammonemia of the Newborn ?

A transitory symptomatic hyperammonemia may occur in newborns born at 34 to 36 weeks’ gestation. The clinical features are respiratory distress and lethargy progressing to seizures and coma within 4 days after birth. Pupillary dilation is common.

Initial plasma ammonia concentrations are 800 to 3400 μg/dL but may peak as high as 7600 μg/dL. No deficiency of urea-cycle enzymes is demonstrable. Although the cause of hyperammonemia cannot be determined, affected newborns respond rapidly and completely to either exchange transfusion or dialysis. THAN survivors have normal neurological and developmental evaluations later on and do not experience recurrent episodes of hyperammonemia.

This symptomatic hyperammonemia may be an exaggeration of a physiological, nonsymptomatic hyperammonemia detected in more than 50% of prematures that does not require treatment.

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