Pediatric emergency medicine trisk 2417 2417
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Diseases involving the same metabolic pathways or organelles usually share similar
features. Thus, recognition and treatment does not require specific knowledge of IEMs, but
rather a general understanding of diagnostic categories and disease pathways.
Most IEMs with potential for acute decompensation present in neonates or infants but may
present in older children and adolescents.
Common clinical manifestations of acute decompensation include vomiting, lethargy,
seizures, rapid deep breathing, hypothermia, or brief resolved unexplained event (BRUE).
Metabolic acidosis, respiratory alkalosis, hypoglycemia, and/or hyperammonemia are
laboratory hallmarks of IEM. Pretreatment samples should be sent for testing when possible
as laboratory studies may become normal with treatment.
Prompt emergency treatment of physiologic decompensation, using PALS or APLS
guidelines, correction of metabolic derangements, as well of precipitant causes of
decompensation are critical for optimizing outcome.
Current Understanding
IEMs are usually caused by single gene defects that result in abnormalities in protein, carbohydrate, fat,
or complex molecule metabolism. Most are due to a defect in, or deficiency of, an enzyme, enzyme
cofactor, or transport protein that results in a block in a metabolic pathway. Clinical effects are the
consequence of toxic accumulations of substrates before the block or intermediates from alternative
metabolic pathways and/or defects in energy production and utilization due to deficiency of products
beyond the block. Common clinical presentations of IEMs are detailed in Table 95.1 .
In the ED, evaluation and management of patients with undiagnosed but suspected IEM is usually
guided by suspicion of metabolic disease but does not require a specific diagnosis. Categories of IEMs
and their clinical and laboratory findings are detailed in Table 95.2 . Patients with an organic acidemia,
urea cycle defect, disorder of carbohydrate utilization or production, fatty acid oxidation defect,
mitochondrial disorder, or peroxisomal disorder are at greatest risk of acute, life-threatening
decompensation. Patients with congenital adrenal hyperplasia, detailed in Chapter 89 Endocrine
Emergencies , may also present with acute critical decompensation.
Toxic accumulation of substances results from disorders of protein metabolism (i.e.,
aminoacidopathies, organic acidemias, urea cycle defects), carbohydrate intolerance, and lysosomal
storage disorders. Defects in energy production or utilization result from disorders of glycogenolysis and
gluconeogenesis, fatty acid oxidation defects, and mitochondrial disorders. Peroxisomal disorders are a
diverse group of IEMs caused by defects of single or multiple peroxisomal enzymes, or of peroxisomal
biogenesis that result in toxic accumulations, energy deficiency, and/or defects in biosynthesis of
complex molecules. Other categories include disorders of metal metabolism, purine, and pyrimidine
biosynthesis (e.g., Lesch–Nyhan syndrome); cholesterol biosynthesis, heme, bile acid, and bilirubin
metabolism, lipoprotein metabolism, and glycosylation.
