all suspicious cases, obtain appropriate cultures (eg, blood, cerebrospinal fluid, and urine) and consider appropriate antibiotics. Because infection can exacerbate metabolic disease, it should be considered even when a metabolic disorder is likely.
B. Organic Acidemia. Most often caused by enzyme or cofactor deficiencies in the catabolism of branched chain amino acids (valine, leucine, and isoleucine). Organic acid and a positive gap acidosis develop from metabolites built up behind the enzymatic block. Other effects of metabolite excess include inhibition of enzymes of the urea cycle with secondary hyperammonemia. Many of these metabolites have direct CNS toxicity. Marrow suppression and altered glucose metabolism (hyperglycemia or hypoglycemia) also can occur as secondary effects.
C. Primary Urea Cycle Defects. Typically result in hyperammonemia without acidosis. Hallmark of these disorders is respiratory alkalosis in an ill-appearing child; hyperammonemia affects the respiratory centers, causing deep and rapid breathing (hyperp-nea) with resultant drop in carbon dioxide.
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