Pediatric emergency medicine trisk 2450 2450
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phosphatase, bilirubin, ammonia, plasma amino acid levels, CBC, and urinalysis should be obtained. All
labs except ammonia may be normal. Even patients who are not lethargic may have significant
hyperammonemia, masked by acclimatization to chronic elevations of ammonia.
Management
Immediate treatment of hyperammonemia is important to prevent morbidity and mortality ( Table 95.7 ).
Rapid consultation with an IEM specialist is crucial and central venous access may be needed. Protein
intake should be temporarily withheld (not longer than 36 to 48 hours). Although patients with urea cycle
defects are usually not hypoglycemic, dextrose should be provided in IV fluids (along with IV lipids at 1
to 3 g/kg/day) at typically 1.5 times the maintenance rate in order to maintain hydration and prevent
catabolism. IV Ammonul (sodium phenylacetate and sodium benzoate) is given via central line as a bolus
followed by 24-hour infusion in order to correct hyperammonemia. Arginine may also be used (except
those with arginase deficiency) and citrulline is used in CPS1 and OTC deficiencies to correct
hyperammonemia. Sodium chloride (not Ringer lactate) can be used to correct dehydration but should be
used with extreme caution when giving Ammonul, which is high in sodium and/or arginine, which is high
in chloride. Although patients with urea cycle defects have low levels of carnitine and may be taking L carnitine as a routine medication, patients should not receive L -carnitine while being treated with
Ammonul because it conjugates and inactivates sodium benzoate. For treatment of seizures, valproic acid
should be avoided because it decreases urea cycle activity and may therefore worsen hyperammonemia.
The New England Consortium of Metabolic Programs details treatment for specific urea cycle defects on
their
website
.
FATTY ACID OXIDATION DEFECTS
Goals of Treatment
Goals specific for the treatment of the patient with a fatty acid oxidation defect are to correct acidosis and
hypoglycemia which should correct hyperammonemia, if present.
Clinical Understanding
Disorders include enzyme deficiencies involving metabolism of short, medium, long, and very long-chain
fatty acids and carnitine transport defects. Medium-chain acyl-CoA dehydrogenase deficiency is not only
the most common fatty acid oxidation defect but also one of the most common IEMs with an incidence of
approximately 1/10,000. Patients with a fatty acid oxidation defect usually present in infancy between
ages 3 months and 2 years due to longer overnight fasts as the infant begins sleeping through the night or
due to increased metabolic demand caused by intercurrent illness, often gastroenteritis, recent surgery, or,
particularly in children and adolescents, vigorous exercise. Normally in these scenarios, inadequate
glucose availability to meet caloric demands results in catabolism of fatty acids, which are oxidized in the
mitochondria to acetyl CoA, which is used to produce ketones to meet energy needs. In fatty acid
oxidation defects, accumulation of fatty acid metabolites inhibits gluconeogenesis, causes metabolic
acidosis and has hepatotoxic effects. Inadequate energy leads to impairment of skeletal and cardiac
muscle.
Current Considerations
Assessment
Early manifestations of decompensation may include lethargy, dehydration, vomiting and/or diarrhea,
hepatomegaly, and usually hypoglycemia with absent or inappropriately low ketones (except in patients
with short-chain acyl-CoA deficiency who often produce ketones). Decompensation may progress within
hours to encephalopathy, coma, cardiac dysfunction (heart failure or pericardial effusion), liver
