Metabolic emergencies in infants and children

1. THE 2-MINUTE PHYSIOLOGY (Rapid Pathophysiology)

• The Enzymatic Blockade: Inborn errors of metabolism (IEM) are caused by genetic defects in specific enzymes or co-factors that disrupt normal metabolic pathways. This results in two catastrophic events: the toxic accumulation of upstream substrates (and diversion into harmful alternative pathways) and the critical deficiency of downstream products (primarily energy/ATP).
• The Catabolic Crisis: The core driver of the clinical presentation in the ED is a state of metabolic stress (triggered by fasting, fever, or concurrent illness like sepsis). The child enters a hyper-catabolic state, breaking down proteins and fats rapidly.
• Toxic Accumulation:
• Urea Cycle Defects: Breakdown of amino acids leads to massive ammonia accumulation, causing direct neurotoxicity and cerebral edema.
• Organic Acidurias: Accumulation of organic acids causes profound anion gap metabolic acidosis.
• Fatty Acid Oxidation Disorders: Inability to utilize fats for energy during fasting leads to severe non-ketotic hypoglycemia and energy failure.

2. THE BEDSIDE ACTION PLAN (Rapid ER Management)

• Immediate Stabilization: Assess ABCs, provide supplemental oxygen, establish rapid IV/IO access, and obtain a stat point-of-care (POC) blood glucose.
• Halt Enteral Toxins: Immediately make the child strictly NPO to stop the intake of offending substrates (e.g., proteins or specific sugars).
• Reverse Catabolism (The Metabolic Resuscitation): You must stop the body from breaking down its own tissues. Administer IV D10W with 0.45% Normal Saline at 1.5 times the maintenance rate. Note: Administer dextrose-containing fluids immediately even if the exact metabolic diagnosis is unknown.
• Hyperammonemia Rescue: If the patient exhibits neurologic signs and profound hyperammonemia, the neurologic outcome correlates directly with the duration of the ammonia elevation. Administer IV sodium benzoate and sodium phenylacetate (Ammonul) as ammonia scavengers.
• The Emergency Protocol: For children with a known diagnosis, immediately ask the parents for their emergency care plan or emergency information form and follow its exact medication and fluid parameters. Consult the metabolic geneticist early.

3. THE DIAGNOSTIC GRID (Differential Diagnosis & Workup)

• Top "Can't-Miss" Mimics:
• Sepsis: The ultimate mimic. Neonatal sepsis presents identically to an IEM (lethargy, hypothermia, shock), and critically, an infection often triggers a metabolic crisis.
• Ductal-Dependent Congenital Heart Disease: Presents with cardiogenic shock and severe acidosis in the first few weeks of life.
• Abusive Head Trauma / Intracranial Hemorrhage: Presents with isolated encephalopathy, seizures, and lethargy.
• Prioritized Diagnostic Workup:
• Tier 1 (The "Big Four"): To cover the common pathways of hundreds of different IEMs, you must rapidly order four specific tests: Ammonia, Glucose, Ketones, and Lactate.
• Tier 2 (ED Adjuncts): Basic metabolic panel (calculate the anion gap), blood gas analysis (assess pH and base deficit), and CBC/blood cultures (to rule out concurrent sepsis). Check the state newborn screening results if available.
• Tier 3 (Definitive Diagnosis): Draw extra blood and freeze it prior to transfusions. Send plasma amino acids, acylcarnitine profile, and urine organic acids.

4. THE VISUAL BOARD (ECG / POCUS / Imaging)

• Non-Contrast Head CT: Obtain rapidly if the child is comatose, has focal neurologic deficits, or has suspected hyperammonemia, to evaluate for acute cerebral edema or rule out intracranial hemorrhage.
• Point-of-Care Ultrasound (POCUS): Perform a focused bedside echocardiogram. Certain metabolic disorders (e.g., Pompe disease or fatty acid oxidation defects) can cause profound dilated or hypertrophic cardiomyopathy. Evaluate global cardiac contractility.
• ECG: Evaluate for electrolyte-induced arrhythmias, specifically looking for signs of hyperkalemia or hypocalcemia which can be driven by severe metabolic acidosis and acute kidney injury.

5. THE SCORING MATRIX (Risk Stratification & Guidelines)

• The Universal Pediatric Assessment Triangle (PAT): Used to rapidly identify the crashing infant (Appearance, Work of Breathing, Circulation to Skin).
• Newborn Screening ACT Sheets: If a neonate presents with a known abnormal newborn screen, immediately access the American College of Medical Genetics and Genomics (ACMG) ACT sheets and algorithms online. These are the gold-standard, validated risk-stratification tools that dictate exactly what the abnormal screen means and what immediate emergency actions are required.

6. THE DANGER ZONE (Pitfalls & Critical Actions)

• The Sepsis Tunnel Vision: Pitfall: Assuming a lethargic, hypotensive neonate only has sepsis and failing to order an ammonia level. Critical Action: Always order an ammonia level and a bedside glucose alongside your sepsis workup in the undifferentiated crashing infant.
• The Fluid Resuscitation Trap: Pitfall: Resuscitating the child solely with normal saline. Critical Action: You must provide substrate to stop catabolism. Administer dextrose-containing IV fluids early and aggressively.
• Ignoring the Binder: Pitfall: Attempting to calculate complex metabolic pathways from memory when a known IEM patient arrives. Critical Action: Listen to the parents. If they hand you an emergency letter or protocol from their geneticist, follow it immediately and call the specialist.

7. MCQ MASTERCLASS (Written Exam Tips)

• Buzzword: “Normal at birth, then progressive lethargy, vomiting, and seizures after the introduction of formula/breast milk.”
• Diagnosis: Inborn error of metabolism (amino acid or urea cycle defect triggered by protein load).
• Buzzword: “Hypoglycemia with ABSENT ketones in the urine.”
• Diagnosis: Fatty acid oxidation disorder (e.g., MCAD deficiency). The body cannot make ketones from fat, so it depletes glucose and crashes.
• Common Distractor: A lethargic 10-day-old infant is brought to the ED. The bedside glucose is 35 mg/dL. An option suggests "Administer empiric antibiotics and perform a lumbar puncture." Differentiate: While a full sepsis workup is required, the immediate correct answer must address the life-threat: "Administer IV D10W." Furthermore, always select the option that includes checking a serum ammonia level in an undifferentiated encephalopathic neonate.

8. THE BOARDROOM SCRIPT (OSCE & Oral Board Tips)

• The Opening Salvo: "This is a critically ill infant presenting with undifferentiated shock and encephalopathy. My immediate priorities are to secure the airway, provide 100% oxygen, establish IO or IV access, and obtain a stat point-of-care blood glucose."
• Articulating the Resuscitation: "Given the lack of a clear etiology, I must concurrently treat for sepsis and a metabolic crisis. I am making the child strictly NPO to halt enteral toxin production. I will administer a 20 mL/kg normal saline bolus for perfusion, but I am immediately starting a maintenance fluid of D10 half-normal saline at 1.5 times the maintenance rate to reverse catabolism."
• Ordering the "Metabolic Cocktail": "In addition to blood cultures and broad-spectrum antibiotics, I am ordering the critical metabolic labs: a stat serum ammonia, plasma lactate, urine ketones, and a blood gas. I will ask the parents if there is a known abnormal newborn screen or an emergency care plan from a geneticist, and I will consult the pediatric intensivist and metabolic specialist for admission."