Metabolic Diseases in Acidotic Newborns
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- Metabolic acidosis is a common acute presentation of an inborn error of metabolism (IEM), particularly in the presence of elevated anion gap. Acidosis can also be seen as a result of hypoperfusion, congenital heart disease, sepsis, liver failure, toxic ingestion, and diabetic ketoacidosis (DKA).
- IEMs are generally defects of protein, fat, or carbohydrate metabolism or of the mitochondrial respiratory chain that result in either accumulation or deficiency of a metabolite.
- IEMs should be considered early in the workup of a child with metabolic acidosis in order to detect those conditions that are treatable prior to development of permanent neurologic sequelae. Sequelae can be related to duration and severity of exposure. Basic evaluation for IEMs should be undertaken concurrently with other diagnostic evaluations.
Infants with IEMs are at increased risk for decompensation and acute presentation in cases of infection, fever, fasting, or other causes of catabolism.
Generally autosomal recessive, with the exception of pyruvate dehydrogenase deficiency (X-linked dominant), ornithine transcarbamylase (X-linked), and some diseases of the mitochondrial genome (maternally inherited)
- Avoid propofol if possible (anecdotal increase in pancreatitis).
- Avoid prolonged fasting or nutritional deprivation.
- Avoid use of systemic steroids whenever possible (steroids may increase the metabolic demands).
Metabolic acidosis is often a downstream effect of the primary metabolic abnormality. A block in normal metabolism can result in dysfunction of the mitochondrial respiratory chain, buildup of toxic intermediates, disordered or reduced energy production, buildup of waste nitrogen in the form of ammonia and specific amino acids, and through conjugation of the acids with carnitine, lead to carnitine depletion. These events can lead to multiorgan dysfunction including the following:
- CNS toxicity: edema, neurologic effects of hypoglycemia, toxic encephalopathy
- Cardiac: arrhythmias, left ventricular noncompaction cardiomyopathy
- Liver: hepatosplenomegaly, elevation of liver function tests, prolonged hyperbilirubinemia
- Hematologic: bone marrow suppression
- Renal: proximal tubule dysfunction, kidney failure (typically later onset)
Multifactorial. Primary metabolic disease is typically due to a genetic defect that causes a block in metabolism resulting in buildup of toxic intermediates or absence/reduction of necessary downstream products.
Commonly Associated Conditions
- Maternal hemolysis, elevated liver enzymes, low platelets (HELLP), fatty liver of pregnancy, preeclampsia: associated with specific fetal disorders of fatty acid oxidation
- Metabolic stroke: stroke affecting the basal ganglia (not ischemic or hemorrhagic in character)