Emergency Medicine Hub / Pediatrics & Obstetrics • 3 min read • 2 sections

Inborn Errors of Metabolism & Neonatal Hypoglycemia

Comprehensive emergency evaluation and protocolized resuscitation of inborn errors of metabolism (IEM) presenting in the neonate and infant: acute metabolic decompensation following protein feeds or fasting, distinguishing Urea Cycle Disorders (UCDs) from Organic Acidemias and Fatty Acid Oxidation Disorders (FAODs), diagnostic algorithm using blood gas anion gap, blood glucose, and serum ammonia; emergency management of hyperammonemic coma (nitrogen scavengers, hemodialysis), and critical pediatric hypoglycemia boluses (D10W).

Resuscitation Quick Actions • First 2 Minutes

High-Acuity

Critical First Three Labs

1) Serum Ammonia (on ice), 2) Blood Gas + Electrolytes (anion gap), 3) Blood Glucose (rule out hypoglycemia)

Pediatric Hypoglycemia Bolus

Dextrose 10% (D10W) 2 mL/kg IV bolus (never use D50W in children; causes severe hyperosmolar brain injury and tissue necrosis)

Dextrose Infusion Rate

Start D10W at 1.5x maintenance to provide Glucose Infusion Rate (GIR) of 8–10 mg/kg/min to shut down catabolism

Hyperammonemic Dialysis

Serum ammonia > 500 mcmol/L (or > 250 with encephalopathy refractory to meds) = STAT CONTINUOUS HEMODIALYSIS

Nitrogen Scavengers

Sodium Phenylacetate + Sodium Benzoate (Ammonul) 250 mg/kg IV over 90–120 min to clear nitrogen without urea cycle

Stop All Protein Intake

Halt all formula, breast milk, and protein feeds immediately; supply 100% calories from glucose and IV lipids

Bottom-Line Clinical Pearl

Suspect an Inborn Error of Metabolism (IEM) in any previously healthy neonate who develops sudden deterioration (lethargy, poor feeding, intractable vomiting, tachypnea, seizures, or coma) around days 3–7 of life following the introduction of protein-rich breast milk or formula. The initial diagnostic triage requires THREE simultaneous tests: (1) Blood Gas (anion gap metabolic acidosis vs. respiratory alkalosis), (2) Blood Glucose (hypoglycemia vs. normoglycemia), and (3) Serum Ammonia. High ammonia (> 150–200 mcmol/L) with respiratory alkalosis indicates a Urea Cycle Defect; high ammonia with high anion gap metabolic acidosis and urine ketones indicates an Organic Acidemia. Stop all protein intake immediately, infuse 10% Dextrose (D10W at 1.5x maintenance) to suppress catabolism, and initiate emergent hemodialysis if ammonia > 500 mcmol/L.

1. Diagnostic Branching: Ammonia, Acidosis & Glucose

A full-term infant with an uneventful birth who is discharged home healthy, but returns between days 3 and 7 of life with vomiting, encephalopathy, hypothermia, or seizures is suffering from either neonatal sepsis, a duct-dependent cardiac lesion, or an Inborn Error of Metabolism (IEM). The three foundational emergency screening tests branch into distinct pathophysiologic categories:

Serum Ammonia	Blood Gas & Anion Gap	Blood Glucose & Urine Ketones	Diagnostic Category & Exemplar Diseases
Severely Elevated (> 200 to 1,000+ mcmol/L)	Respiratory Alkalosis (pH > 7.45, low pCO2, normal anion gap)	Normal Glucose; Absent Urine Ketones	Urea Cycle Disorders (UCDs): Ornithine transcarbamylase (OTC) deficiency (X-linked; #1 UCD), Citrullinemia, Argininosuccinic aciduria. Ammonia directly stimulates medullary respiratory center causing early tachypnea and respiratory alkalosis.
Elevated (150–500 mcmol/L)	High Anion Gap Metabolic Acidosis (HAGMA) (pH < 7.20, HCO3 < 10, Gap > 16)	Hypoglycemia or Normoglycemia; Massive Urine Ketones	Organic Acidemias: Methylmalonic acidemia (MMA), Propionic acidemia (PA), Isovaleric acidemia (sweaty feet odor). Defective branched-chain amino acid metabolism; secondary inhibition of urea cycle causes moderate hyperammonemia.
Normal to Mildly Elevated	Normal Gap or Mild Acidosis	Severe Hypoglycemia; ABSENT/TRACE Urine Ketones	Fatty Acid Oxidation Disorders (FAODs): Medium-Chain Acyl-CoA Dehydrogenase (MCAD) Deficiency. Inability to generate ketones during fasting stress causes non-ketotic profound hypoglycemia with acute hepatomegaly and cardiac arrest.
Normal to Mildly Elevated	High Anion Gap Metabolic Acidosis	Marked Lactic Acidosis (> 5–10 mmol/L)	Mitochondrial Disorders/Glycogen Storage Diseases: Pyruvate dehydrogenase deficiency, GSD Type I (von Gierke). Massive lactic acidosis and severe hepatomegaly.

2. Emergency Resuscitation & Hyperammonemia Protocols

Step/Intervention	Pharmacologic Regimen	Clinical Goal & Safety Parameters
1. Reverse Catabolism	D10W 2 mL/kg IV bolus, then start D10W at 1.5x maintenance	Provides a Glucose Infusion Rate (GIR) of 8 to 10 mg/kg/min ($GIR = [\%\text{ dextrose} \times \text{rate in mL/hr}]/[6 \times \text{weight in kg}]$); triggers endogenous insulin to shut down protein catabolism.
2. Eliminate Protein	Discontinue all oral and enteral protein feeds immediately	Removes exogenous nitrogen substrate feeding the urea cycle and organic acid cascades.
3. Nitrogen Scavengers	Sodium Phenylacetate + Sodium Benzoate (Ammonul) 250 mg/kg IV in D10W over 90–120 min	Provides non-urea-cycle alternative pathways: benzoate conjugates glycine to form hippurate; phenylacetate conjugates glutamine to form phenylacetylglutamine renally excreted.
4. Emergent Hemodialysis	Vascular access with continuous venovenous hemodialysis (CVVHD) or intermittent HD	Mandatory if ammonia > 500 mcmol/L or failing to drop after 4h of scavengers. Ammonia crosses blood-brain barrier rapidly, producing astrocyte swelling, irreversible cerebral edema, and brainstem herniation.

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