TABLE 95.6 POSTMORTEM SPECIMENS COLLECTED AT AUTOPSY a Postmortem specimens Analyses Blood a 10-mL EDTA tube Chromosome analysis 4–6 filter paper spots DNA analysis (requires PCR amplification) 5-mL heparinized tube Tandem mass spectrometry for organic acidemias, urea cycle defects, fatty acid oxidation defects Acylcarnitines Amino acids Bile acids Urine a Urine 10 mL in 1–2-mL Amino acids aliquots Organic acids Acylcarnitines Bile acids Cerebrospinal fluid (CSF) CSF 3–5 mL in 1-mL Glucose aliquots Lactate, pyruvate Glycine, serine Neurotransmitters Organic acids Aqueous humor Aqueous humor Organic acids Skin biopsy a Skin—2 samples, 3-mm Chromosome analysis diameter each DNA analysis Enzyme activity Comments on collection, storage Obtain blood by vascular access or intracardiac puncture For filter paper spots, apply free-flow blood to filter paper, saturate through to back, not layer drops Air-dry 3–4 hrs, not heat Place in envelope, refrigerate Freeze plasma at −20°C or −70°C, store erythrocytes at 4°C Collect by bladder catheterization, suprapubic aspiration If unsuccessful, irrigate bladder with 20mL normal saline and collect or perform intrabladder swabs at autopsy Freeze at −20°C or −70°C If not collected for clinical care, may be appropriate to collect postmortem Freeze at −20°C or −70°C May be appropriate if blood not available Collect by intraocular puncture at autopsy Freeze at −20°C or −70°C Best collected premortem or immediately postmortem, usually viable 2–3 days, wk may be helpful to discuss with specialist Skin, punch, or incisional biopsy, sterile technique, sites—flexor surface forearm, anterior thigh, transport in sterile tube completely filled with tissue culture media, viral culture media (do not use culture media if planning for microscopic studies), normal saline without preservative, or normal saline–soaked sterile gauze in sterile tube, freeze at –70°C Fibroblast culture provides unlimited specimen Organ biopsy Brain b Heart muscle b Liver a cm3 , 10–20 mg, ≤0.5 cm thick Kidney b Histochemical light and/or electron Biopsy potentially affected organs, microscopy collect within 1–2 hrs after death Enzyme activity Biochemical metabolites Mitochondrial studies Spleen b Skeletal muscle 20–50 mg, ≤0.5-cm thick Bile Bile mL Needle or open incisional biopsy, sterile technique, wrap in aluminum foil, dry ice, freeze at −70°C, screw-top airtight vial Some assays may need to be performed on fresh specimens Bile acids Acylcarnitines a If family declines autopsy but gives permission for specimen collection, or if unable to obtain autopsy within hours of death, collect blood, urine, and CSF; perform punch or open incisional biopsy of skin and needle biopsy of liver and skeletal muscle; take photographs of dysmorphic features; and obtain radiologic studies to evaluate for neurologic, cardiac, or skeletal abnormalities Obtain parental permission Tests that are not accurate using postmortem specimens are those for serum amino acids, lactate, pyruvate, and total and free carnitine assessment Consider developing postmortem specimen collection kit for ED that contains necessary equipment, specimen containers, and institution-specific instructions b Obtain an autopsy if autopsy permission granted EDTA, ethylenediaminetetraacetic acid; PCR, polymerase chain reaction; ED, emergency department Hyperammonemia is the hallmark of urea cycle defects but also occurs in organic acidemias and fatty acid oxidation defects as a consequence of secondary inhibition of the urea cycle Ammonia levels are typically highest in urea cycle defects and may exceed 1,000 μg/dL Ammonia levels in organic acidemias are usually less than 500 μg/dL during decompensation but may exceed 1,000 μg/dL Hyperammonemia in fatty acid oxidation defects, if present, is usually less than 250 μg/dL Transient hyperammonemia of the newborn should be considered in the differential diagnosis, particularly if hyperammonemia is present on the first day of life Hyperammonemia directly stimulates the respiratory center, resulting in tachypnea Ammonia level higher than 250 μg/dL with respiratory alkalosis in the absence of metabolic acidosis is highly suggestive of a urea cycle defect Proper collection and handling of blood for ammonia determination is critical to prevent falsely elevated values Abnormal levels should be confirmed immediately using proper technique for drawing and handling Patients with urea cycle defects may have compensatory metabolic acidosis Patients with organic acidemias and fatty acid oxidation defects and hyperammonemia have primary metabolic acidosis usually without respiratory alkalosis Patients with hyperammonemia due to organic acidemias usually have marked ketosis and normal glucose level, whereas those with fatty acid oxidation defects usually have hypoketotic hypoglycemia Even during minor illnesses, protein catabolism may result in hyperammonemia In patients with hyperammonemia, liver function should be evaluated Mild elevation of transaminases may be seen in metabolic disorders in each category Plasma should be sent for amino acids and acylcarnitines evaluation, and urine for organic acids, acylglycines, and orotic acid evaluation Liver dysfunction due to causes other than IEM, including primary liver disease, hepatic infection, toxic insult, sepsis, and asphyxia, may also cause hyperammonemia Imaging studies In the ED, imaging studies may be useful to guide management of potential acutely life-threatening organ system failure, particularly cerebral edema, hemorrhagic or thrombotic stroke, or cardiac failure Imaging studies to aid in diagnosis and long-term management are rarely appropriate in the ED setting Management Initial treatment of IEMs is aimed at correcting acute metabolic abnormalities with an empiric focus on preventing further catabolism Even the apparently stable patient may deteriorate rapidly For patients with IEMs of amino acid or carbohydrate metabolism, treatment is aimed at elimination of toxic metabolites For disorders of fatty acid oxidation or gluconeogenesis and glycogenolysis, therapy is aimed at correcting the energy deficiency In patients with lysosomal, mitochondrial, and peroxisomal disorders, emergent treatment is aimed at ameliorating the effects of organ dysfunction and usually involves temporizing measures that not have long-term impact on the inevitable progressive, degenerative course of these disorders As always, airway, breathing, and circulation must be addressed first Treatment for a potential IEM should be started empirically as soon as the diagnosis is considered ( Table 95.7 ) All oral intake should be stopped to prevent the introduction of potentially harmful protein or sugars Fluid bolus(es), as clinically indicated, should be normal saline, 10 mL/kg for neonates or patients with concern of heart failure and 20 mL/kg for infants and children Ringer lactate should be avoided because it can worsen acidosis The initial fluid bolus should be followed by dextrose-containing (typically at a dextrose concentration of at least 10%) IV fluids typically administered at 1.5 times maintenance rate to prevent catabolism Hypoglycemia Hypoglycemia, if present, should be corrected by dextrose bolus instead of adding D10 to bolus fluid; 0.25 to g/kg as 10% dextrose for neonates, and 10% or 25% dextrose for those beyond the neonatal period Hydration after fluid/dextrose bolus should be with D10 to D15 in ½ normal saline at to 1.5 times maintenance to maintain serum glucose level at 120 to 170 mg/dL, with the goal of preventing catabolism Large, rapid fluctuations in glucose level should be avoided Correction of hypoglycemia with glucose will improve most conditions with the exception of primary lactic acidosis due to disorders of gluconeogenesis involving pyruvate metabolism Acidosis Sodium bicarbonate may be used in some limited circumstances for the immediate treatment of metabolic acidosis, however, is likely to have minimal impact if the underlying metabolic cause is not treated Rapid and/or overcorrection of acidosis may have adverse CNS effects In the patient with hyperammonemia, alkalization of the blood favors the conversion of NH4 + to NH3 , which crosses the blood–brain barrier more readily and may cause cerebral edema and/or hemorrhage Furthermore, alkalization of the urine decreases excretion of ammonia Ultimately, definitive treatment of acidosis requires removal of the abnormal metabolites either by restricting dietary intake, or in severe cases, by dialysis, preferably hemodialysis Hyperammonemia Significant hyperammonemia is life threatening and must be treated immediately Treatment protocols for hyperammonemia in neonates and infants and children are detailed on the New England Consortium website and as per their site are meant to be used in consultation with an IEM specialist: https://newenglandconsortium.org/for-professionals/acute-illness-protocols/urea-cycledisorders/neonate-infant-child-with-hyperammonemia/ The goals of emergent treatment of hyperammonemia are to eliminate protein intake, prevent catabolism, and enhance the elimination of ammonia Central venous access is required for treatment Fluid containing 10% to 20% dextrose at a rate of to 1.5 times maintenance to maintain serum glucose level at 120 to 170 mg/dL should be administered to prevent catabolism and enhance elimination of ammonia If hyperglycemia occurs, ... autopsy permission granted EDTA, ethylenediaminetetraacetic acid; PCR, polymerase chain reaction; ED, emergency department Hyperammonemia is the hallmark of urea cycle defects but also occurs in organic