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INTRODUCTION

Metabolic emergencies are challenging childhood disorders, often presenting with nonspecific signs and symptoms that may mimic more common conditions such as sepsis. Delay in accurate diagnosis can lead to significant morbidity and mortality, whereas early aggressive management can be lifesaving and reduce long-term neurologic sequelae. Individually, these disorders are uncommon, but taken together as an entity, they are likely to be encountered by most emergency providers, who must be familiar with the general steps to facilitate expedited emergency management.

In any healthy neonate, sudden acute deterioration should prompt consideration of metabolic disease. Vomiting, altered mental status, and poor feeding are the most common clinical features of metabolic emergencies. Appropriate management can be started in the ED without a definitive diagnosis. This chapter reviews the most common metabolic disorders presenting as acute decompensation in the young infant and their emergency management. Hypoglycemia is discussed separately. Congenital adrenal insufficiency is included here because of the overlap in presentation with other inherited metabolic disorders and the importance of prompt recognition and treatment in the critically ill neonate. Inherited metabolic disorders that present in later childhood, such as lysosomal storage diseases, are often diagnosed and managed outside of the ED and so are not included here.

HYPOGLYCEMIA

Hypoglycemia is defined as at least one blood glucose concentration <47 milligrams/dL (2.65 mmol/L); it is considered severe if the glucose concentration is <36 milligrams/dL (2 mmol/L) and recurrent if three or more episodes have occurred.1 Hypoglycemia also includes any glucose concentration low enough to cause symptoms or signs of impaired brain function.2 Transient neonatal hypoglycemia (within 48 hours of birth) has been linked with a decreased proficiency on literary and mathematics fourth-grade achievement tests, as well as low executive and visual motor function.1,3 This makes detection and treatment of neonatal hypoglycemia especially important to avoid long-term negative neurodevelopmental outcomes.

PATHOPHYSIOLOGY

Neonates are born with 60% to 80% of maternal glucose levels. Within 2 to 4 hours, neonates begin to regulate their own serum glucose levels, and the majority of transient hypoglycemic episodes resolve within 48 hours of birth. Any hypoglycemic episode after 48 hours of birth requires a detailed evaluation to identify the cause. Maintenance of serum glucose depends on intake and endogenous gluconeogenesis and glycogenolysis mediated by various hormones. Serum glucose level is affected when there is an imbalance between insulin (a hypoglycemic hormone) and its counterregulatory hormones cortisol, growth hormone, glucagon, and epinephrine (hyperglycemic hormones). Insulin stimulates cellular glucose uptake and suppresses lipolysis, whereas hyperglycemic hormones stimulate lipolysis and glycogenolysis. Excess insulin (hyperinsulinemia) results in hypoglycemia with the absence of urinary ketones. Hypoglycemia in the neonate or infant may result from inadequate oral intake, excess insulin, deficient hyperglycemic hormones (e.g., growth hormone or adrenal hormone deficiency), disorders of fatty acid oxidation or carbohydrate metabolism, aminoacidopathies and organic acidurias (due to inhibition of gluconeogenesis), or severe systemic illness (e.g., sepsis). Infants of diabetic mothers, postterm infants, and large for gestational age infants are at risk for hypoglycemia due to ...

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