6.2 Electrolyte Imbalances & Inborn Errors of Metabolism

Overview of Pediatric Metabolic & Electrolyte Derangements

Electrolyte homeostasis and cellular metabolism in pediatric patients are governed by tight physiological feedback mechanisms. Because pediatric patients have higher body water composition, rapid turnover of fluids, and immature renal concentrating capabilities, electrolyte derangements develop rapidly during acute illnesses. Furthermore, previously healthy neonates presenting with sudden metabolic decompensation must be urgently evaluated for Inborn Errors of Metabolism (IEM). Prompt clinical recognition and emergency stabilization by the pediatric emergency nurse are crucial to prevent irreversible neurological damage or death.

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Potassium Imbalances: Hyperkalemia & Hypokalemia

1. Hyperkalemia (Serum Potassium > 5.5 mEq/L; Severe > 6.5 mEq/L)

Hyperkalemia is a critical medical emergency in children caused by acute renal failure, massive tissue trauma/rhabdomyolysis, tumor lysis syndrome, DKA, or adrenal insufficiency (congenital adrenal hyperplasia).

Progressive Electrocardiogram (ECG) Changes

As extracellular potassium rises, myocardial membrane excitability is altered in a predictable sequence:

1. Peaked T Waves: Early sign (K+ 5.5–6.5 mEq/L).
2. PR Interval Prolongation & Flattened P Waves: (K+ 6.5–7.5 mEq/L).
3. QRS Widening & ST Segment Depression: (K+ 7.5–8.0 mEq/L).
4. Sine Wave Pattern, Ventricular Fibrillation, or Asystole: (K+ > 8.0 mEq/L).

+-----------------------------------------------------------------------------------------+
|                        HYPERKALEMIA EMERGENCY MANAGEMENT STEPS                          |
+-----------------------+-----------------------------+-----------------------------------+
|  MEMBRANE STABILIZATION|   INTRACELLULAR SHIFTING    |        POTASSIUM ELIMINATION      |
|  Calcium Gluconate 10%|  • Regular Insulin + Dextrose|  • Furosemide (Loop Diuretic)     |
|  (100 mg/kg IV over   |  • Albuterol Nebulizer      |  • Sodium Polystyrene / Lokelma   |
|   5-10 mins)          |  • Sodium Bicarbonate IV    |  • Hemodialysis (Refractory Cases)|
+-----------------------+-----------------------------+-----------------------------------+

Emergency Pharmacotherapy Protocol

• Step 1: Cardiac Membrane Stabilization: If ECG changes or severe hyperkalemia are present, administer Calcium Gluconate 10% at 100 mg/kg IV over 5 to 10 minutes (or Calcium Chloride 10% at 20 mg/kg IV via central line). Calcium antagonizes potassium-induced membrane excitability within 1 to 3 minutes but does not lower serum potassium.
• Step 2: Intracellular Potassium Shifting:
  • Insulin & Dextrose: Administer Regular Insulin 0.1 units/kg IV with D10W (5 mL/kg IV) to drive potassium into cells.
  • Inhaled Albuterol: Continuous nebulized albuterol (10–20 mg) stimulates beta-2 receptors, shifting potassium intracellularly.
  • Sodium Bicarbonate: 1 to 2 mEq/kg IV over 10–15 minutes (if metabolic acidosis is present).
• Step 3: Potassium Excretion: Administer Furosemide (1 mg/kg IV), potassium-binding resins (Lokelma or Sodium Polystyrene Sulfonate), or initiate emergent hemodialysis.

2. Hypokalemia (Serum Potassium < 3.5 mEq/L)

Caused by gastroenteritis, prolonged vomiting, diuretic therapy, or DKA recovery. Clinical manifestations include muscular weakness, hyporeflexia, ileus, cardiac dysrhythmias, and ECG alterations (flattened T waves, ST depression, prominent U waves).

• IV Replacement Safety: Parenteral potassium chloride (KCl) must be diluted. The maximum peripheral IV infusion rate is 0.25 to 0.5 mEq/kg/hour (maximum 10 to 20 mEq/hour). Continuous cardiac telemetry is required for IV infusions > 0.25 mEq/kg/hr. NEVER administer IV push potassium.

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Sodium & Osmolality Emergencies: Hyponatremia & Hypernatremia

Hyponatremic Seizures

When serum sodium falls acutely below 120–125 mEq/L, water moves osmotically into brain cells, causing acute cerebral edema and seizures. The priority intervention for active hyponatremic seizures is 3% Hypertonic Saline at 3 to 5 mL/kg IV bolus over 10 to 15 minutes (repeating once if seizures persist) to raise serum sodium by 3 to 5 mEq/L and arrest seizure activity.

Hypernatremic Dehydration

In hypernatremic dehydration (Na+ > 145 mEq/L), brain cells synthesize idiogenic osmoles to retain fluid. If IV rehydration is administered too rapidly with hypotonic fluids, water rushes into brain cells, triggering severe cerebral edema, seizures, and permanent brain damage. Serum sodium must be lowered slowly at a rate not exceeding 0.5 mEq/L/hour (or 8 to 10 mEq/L per 24 hours) over a period of 48 to 72 hours.

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Inborn Errors of Metabolism (IEM) in Neonates

Inborn Errors of Metabolism comprise inherited genetic disorders of enzyme deficiencies involved in carbohydrate, protein, or fatty acid metabolism. In neonates, IEM typically manifests after an asymptomatic period of 24 to 72 hours following the introduction of enteral protein (breastmilk or formula) feeding.

Clinical Presentation & Warning Signs

A previously healthy, full-term neonate presenting with:

• Rapidly deteriorating lethargy, poor feeding, hypothermia, and hypotonia.
• Intractable vomiting, tachypnea, and unexplainable seizures.
• Peculiar body odors (e.g., sweet maple syrup odor in MSUD, sweaty feet odor in Isovaleric Acidemia).

Diagnostic Triad of Neonatal IEM

1. Hyperammonemia (Plasma ammonia > 150 to 200 µmol/L in neonates; > 500 µmol/L in Urea Cycle Defects).
2. Severe Metabolic Acidosis with Elevated Anion Gap (Organic Acidemias such as Methylmalonic or Propionic Acidemia).
3. Hypoglycemia with Absent Ketones (Fatty Acid Oxidation Defects such as MCAD deficiency).

+-----------------------------------------------------------------------------------------+
|                           NEONATAL IEM INITIAL STABILIZATION                            |
+-----------------------------------------------------------------------------------------+
|  1. STOP ALL ENTERAL FEEDS (NPO immediately)                                            |
|  2. INITIATE HIGH-RATE IV DEXTROSE (D10W at 1.5x maintenance; GIR 8-10 mg/kg/min)       |
|  3. COLLECT CRITICAL METABOLIC LABS (Ammonia on ice, blood spot, urine organic acids)    |
|  4. ADMINISTER NITROGEN SCAVENGERS / LEVOCARNITINE (Sodium Benzoate / Phenylacetate)     |
|  5. PREPARE FOR EMERGENT HEMODIALYSIS (If plasma ammonia > 400-500 µmol/L)              |
+-----------------------------------------------------------------------------------------+

Emergency Stabilization Protocol

• NPO Status: Immediately stop all oral intake to halt protein and sugar substrate ingestion.
• Suppress Catabolism: Start IV D10W infusion at 1.5 times maintenance to supply a Glucose Infusion Rate (GIR) of 8 to 10 mg/kg/minute, halting endogenous protein catabolism. Add electrolyte coverage but avoid potassium until renal flow is established.
• Ammonia Scavenger Therapy: Administer intravenous nitrogen scavengers (Sodium Benzoate and Sodium Phenylacetate / Ammonul) to eliminate excess ammonia via alternative pathway excretion.
• Hemodialysis: Prepare for emergent hemodialysis or continuous renal replacement therapy (CRRT) if plasma ammonia exceeds 400 to 500 µmol/L or if metabolic acidosis is refractory to medical management.
• Laboratory Sampling: Collect critical baseline specimens before initiating therapy: plasma ammonia (chilled on ice), blood gas, plasma amino acids, urine organic acids, acylcarnitine profile, and newborn screening dried blood spot.