4.2 Pediatric Electrolyte Disturbances: Sodium, Potassium & Calcium Imbalances

Pediatric Electrolyte Disturbances: Sodium, Potassium & Calcium Imbalances

Quick Overview: Electrolyte derangements in pediatric patients produce rapid, life-threatening neurological and cardiac consequences. Because infants have high cell turnover and immature organ clearance, electrolyte abnormalities develop swiftly and demand nuanced intervention. Hyponatremia risks fatal cerebral edema and status epilepticus, while over-rapid correction of hypernatremia risks cerebral edema from idiogenic osmoles. Hyperkalemia alters myocardial membrane stability, progressing from peaked T waves to ventricular fibrillation, requiring immediate sequential emergency therapies. Mastery of safe infusion concentrations, rate ceilings, and clinical signs is essential for the certified pediatric nurse.

Electrolyte disturbances in children reflect disruptions in fluid balance, renal filtration, endocrine regulation, or nutritional intake. The certified pediatric nurse must distinguish between true emergencies requiring rapid membrane stabilization and chronic derangements where rapid correction is itself lethal.

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1. Pediatric Sodium Derangements: Osmolar Homeostasis & Neurological Risks

Sodium is the principal extracellular cation (normal pediatric serum range: 135 to 145 mEq/L) and the primary determinant of serum osmolality. Because water moves freely across semipermeable cell membranes along osmotic gradients, sodium imbalances directly alter intracellular volume, with the central nervous system being the most vulnerable target organ.

Hyponatremia (Serum Sodium < 135 mEq/L)

• Etiology in Pediatric Patients:
  • Improper Formula Preparation: Caregivers stretching commercial infant formula by diluting it with excess water due to economic hardship.
  • Free Water Intoxication: Feeding plain tap water, distilled water, or tea to infants under 6 months of age, whose kidneys cannot excrete excess free water.
  • Swimming Lessons: Accidental swallowing of large volumes of pool water in infant swimming programs.
  • Iatrogenic: Administration of hypotonic intravenous fluids (e.g., 0.2% NS or D5W) in postoperative or hospitalized children.
  • Syndrome of Inappropriate Antidiuretic Hormone (SIADH): Non-osmotic ADH secretion driven by central nervous system infections (meningitis, encephalitis), head trauma, or lower respiratory tract infections (bronchiolitis, pneumonia).
  • Gastroenteritis: Severe sodium-wasting diarrhea treated inappropriately with plain water or fruit juices.
• Pathophysiology: As extracellular sodium drops, serum osmolality falls below intracellular osmolality. An osmotic gradient drives water out of the vascular space into brain cells, producing acute cerebral edema. Because the infant cranium is enclosed (and fontanelles offer only minimal compliance), increased intracranial pressure rapidly compromises cerebral perfusion.
• Clinical Manifestations:
  • Mild to Moderate (125–134 mEq/L): Anorexia, nausea, vomiting, lethargy, apathy, headache, muscle weakness, and hyporeflexia.
  • Severe (<120–125 mEq/L): Progressive hypothermia, profound confusion, stupor, status epilepticus, dilated unreactive pupils, coma, and brainstem herniation (Cushing triad: bradycardia, irregular respirations, severe hypertension).
• Emergency Management Protocol:
  • Active symptomatic seizures: Activate emergency support and give prescribed 3% hypertonic saline under the pediatric symptomatic-hyponatremia protocol. Confirm the weight, concentration, dose, rate, monitoring and reassessment plan; do not treat a single memorized bolus range as universal across institutions. Recheck sodium and symptoms promptly before further correction. Queensland Children's Hospital severe hyponatraemia guideline, updated June 2026.
  • Asymptomatic / Chronic Hyponatremia: Correct slowly. In SIADH, fluid restriction to two-thirds or one-half of maintenance is primary. In hypovolemic hyponatremia, infuse isotonic 0.9% Normal Saline.
  • Rate Limit Caution: In chronic hyponatremia, after emergency symptom control, use the specialist-directed correction target; in a non-seizing child a common target is 6 to 8 mEq/L over 24 hours, avoiding an increase above 8 mEq/L per 24 hours. Rapid correction causes brain cells to dehydrate rapidly, stripping myelin sheaths from pontine neurons and triggering Osmotic Demyelination Syndrome (Central Pontine Myelinolysis), resulting in irreversible spastic quadriparesis, pseudobulbar palsy, and locked-in syndrome.

Hypernatremia (Serum Sodium > 145 mEq/L)

• Etiology:
  • Concentrated infant formula (caregivers failing to dilute liquid concentrate or adding insufficient water to powder).
  • Inadequate fluid intake in breastfed neonates due to delayed lactogenesis or ineffective latch (breastfeeding-associated hypernatremia).
  • High insensible losses (tachypnea, fever, radiant warmers) paired with poor intake.
  • Severe watery diarrhea with high free water loss.
  • Central or Nephrogenic Diabetes Insipidus (DI).
• Pathophysiology: Hypertonic extracellular fluid draws water out of intracellular compartments, leading to intracellular dehydration. Brain tissue shrinks, pulling away from the rigid calvarium. This mechanical traction tears fragile bridging veins, precipitating subdural and subarachnoid hemorrhages and venous sinus thrombosis.
• Clinical Manifestations: Extreme unquenchable thirst, high-pitched shrill cry, fever, hyperreflexia, muscle rigidity, tremors, and a characteristic "doughy" or rubbery skin turgor (skin feels doughy and thickened upon pinching rather than classic tenting). As hypernatremia worsens, children develop lethargy alternating with extreme irritability, convulsions, and coma.
• The Critical Rehydration Trap: Idiogenic Osmoles:
  • Within 24 to 48 hours of hypernatremia, brain cells adapt to protect their volume by synthesizing intracellular osmoprotective molecules called idiogenic osmoles (amino acids, taurine, inositol).
  • If the nurse infuses hypotonic fluids rapidly, extracellular osmolarity falls rapidly while intracellular idiogenic osmoles remain elevated. Water rushes down the osmotic gradient into the hyperosmolar brain cells, causing catastrophic cerebral edema, intractable seizures, and permanent neurological disability.
  • Correction Protocol: Administer maintenance plus deficit fluid slowly over 48 hours. The rate of serum sodium reduction must NOT exceed 0.5 mEq/L/hour, or no more than 10 to 12 mEq/L per 24 hours. Serial serum electrolytes must be monitored every 2 to 4 hours, and if sodium falls too quickly, the IV fluid sodium concentration must be increased.

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2. Pediatric Potassium Derangements: Neuromuscular & Cardiac Excitability

Potassium is the predominant intracellular cation (intracellular: ~150 mEq/L; normal pediatric serum range: 3.5 to 5.0 mEq/L, up to 5.5 to 6.0 mEq/L in neonates). It maintains the resting membrane potential of cardiac myocytes and neuromuscular fibers. Minor shifts in extracellular potassium profoundly alter cardiac conduction.

Hypokalemia (Serum Potassium < 3.5 mEq/L)

• Etiology: Gastrointestinal losses (severe prolonged vomiting, hypertrophic pyloric stenosis with hypochloremic hypokalemic metabolic alkalosis, nasogastric suctioning, profuse diarrhea); renal wasting (loop diuretics like furosemide, thiazides without potassium sparing); intracellular shifting (insulin administration, high-dose albuterol beta-2 agonists, alkalosis); and inadequate nutritional intake.
• Clinical Manifestations: Generalized skeletal muscle weakness, hyporeflexia, muscle cramps, hypotonia, paresthesias, and respiratory muscle weakness. Smooth muscle impairment produces paralytic ileus, presenting with abdominal distension, absent bowel sounds, nausea, and vomiting.
• Electrocardiogram (ECG) Findings:
  • Flattened or inverted T waves
  • ST-segment depression
  • Prominent U waves (characteristic deflection appearing immediately following the T wave)
  • Prolonged PR and QT intervals
  • Ventricular ectopy, premature ventricular contractions (PVCs), and ventricular arrhythmias

Safe intravenous potassium replacement

Potassium is a high-alert medication: never give an IV push or rapid flush. Verify renal function, urine output, serum values, the prescribed concentration, access, and all other potassium sources. Use a premixed preparation and infusion pump under the local pathway. One official pediatric example uses 0.2 mmol/kg/hour on a general ward (maximum 10 mmol/hour) and 0.4 mmol/kg/hour in critical care (maximum 20 mmol/hour), with the required monitoring and laboratory reassessment. These are setting-specific examples, not permission to use a critical-care rate through an unmonitored ward line. Higher concentrations and rapid replacement require appropriate specialist authorization and access. RCH hypokalaemia guideline.

Hyperkalemia (Serum Potassium > 5.0 mEq/L, or > 5.5–6.0 mEq/L in Neonates)

• Step 1: Rule Out Pseudohyperkalemia: In pediatric practice, the most common cause of an elevated potassium lab report is pseudohyperkalemia caused by red blood cell mechanical hemolysis during traumatic heel-stick or finger-stick capillary blood sampling, excessive squeezing ("milking") of the extremity, small needle gauge, or prolonged tourniquet application. Clinical Rule: If the child is completely asymptomatic, has normal renal function, and shows a completely normal baseline ECG, repeat the laboratory test via non-traumatic venipuncture before initiating aggressive therapies.
• True Etiology: Acute kidney injury, end-stage renal disease, massive cellular lysis (tumor lysis syndrome in pediatric leukemias, rhabdomyolysis, extensive full-thickness burns, severe crush trauma), adrenal insufficiency (salt-wasting Congenital Adrenal Hyperplasia [CAH], Addison's disease), severe metabolic acidosis (hydrogen ions shift into cells in exchange for intracellular potassium moving out), and potassium-sparing diuretics.
• Clinical Manifestations: Muscle weakness, paresthesias, ascending flaccid paralysis, diminished deep tendon reflexes, bradycardia, hypotension, and sudden cardiac arrest.
• ECG Progression (The Lethal Sequence):
  1. Mild (5.5–6.5 mEq/L): Tall, peaked, tented T waves with a narrow base (best seen in precordial leads V2–V4).
  2. Moderate (6.5–7.5 mEq/L): Prolonged PR interval, flattened or absent P waves, ST-segment depression.
  3. Severe (7.5–8.5 mEq/L): Marked widening of the QRS complex, blending into the peaked T wave.
  4. Critical (>8.5 mEq/L): Sine-wave pattern, culminating in ventricular tachycardia, ventricular fibrillation, or asystole.

Hyperkalemia Emergency Management Cascade

When true hyperkalemia is accompanied by ECG changes or potassium exceeds 6.5 mEq/L, execute the following three-step prioritized clinical cascade:

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3. Pediatric Calcium Derangements: Neuromuscular Irritability

Total serum calcium ranges from 8.5 to 10.5 mg/dL, while physiologically active ionized calcium ranges from 4.5 to 5.5 mg/dL (1.1 to 1.35 mmol/L). Calcium regulates neuromuscular transmission, cardiac myocyte contraction, and bone ossification, modulated by parathyroid hormone (PTH), calcitonin, and 1,25-dihydroxyvitamin D.

Hypocalcemia (Total Ca < 8.5 mg/dL or Ionized Ca < 4.5 mg/dL)

• Etiology:
  • Hypoparathyroidism, specifically DiGeorge Syndrome (22q11.2 deletion syndrome) characterized by congenital aplasia of the parathyroid glands and thymus, cleft palate, and conotruncal heart defects.
  • Severe nutritional Vitamin D deficiency (rickets).
  • Hypomagnesemia (magnesium is required for PTH release and peripheral tissue sensitivity).
  • Citrate toxicity from massive blood product transfusions (citrate preservative in stored blood chelate-binds free ionized calcium).
  • Acute pancreatitis and sepsis.
• Clinical Manifestations (Neuromuscular Irritability): Jitteriness, tremors, muscle cramping, hyperactive deep tendon reflexes, tetany, carpopedal spasms, high-pitched stridor secondary to laryngospasm, bronchospasm, and seizures.
• Classic Physical Examination Signs:
  • Chvostek Sign: Percussing the facial nerve anterior to the external auditory meatus (over the parotid gland) elicits ipsilateral twitching of the facial muscles, corner of the mouth, or eye.
  • Trousseau Sign: Inflating a blood pressure cuff on the upper arm to 20 mm Hg above the patient's systolic blood pressure for 3 minutes precipitates painful carpopedal spasm (wrist flexion, thumb adduction, metacarpophalangeal flexion with interphalangeal extension—the "main d'accoucheur").
• ECG Findings: Prolongation of the ST segment and QT interval, predisposing the patient to Torsades de Pointes and ventricular dysrhythmias.
• Emergency Treatment: Administer 10% Calcium Gluconate (100 mg/kg or 0.5 to 1.0 mL/kg IV) slowly over 10 to 30 minutes with continuous cardiac monitoring. Rapid administration can trigger severe bradycardia, hypotension, and sinus arrest. Ensure patent IV access; calcium extravasation causes severe chemical thrombophlebitis and subcutaneous tissue necrosis.

Hypercalcemia (Total Ca > 10.5 mg/dL or Ionized Ca > 5.5 mg/dL)

• Etiology: Primary hyperparathyroidism, prolonged immobilization (loss of mechanical stress on long bones causes osteoclastic demineralization, common in pediatric traction or casting), vitamin D or A toxicity, Williams syndrome (idiopathic infantile hypercalcemia with supravalvular aortic stenosis), and pediatric malignancies (leukemias, lymphomas).
• Clinical Manifestations: Often summarized as "bones, stones, groans, and psychiatric moans"—bone pain, osteopenia, nephrocalcinosis and kidney stones, anorexia, nausea, constipation, abdominal pain, pancreatitis, polyuria, polydipsia, lethargy, muscle hypotonia, and confusion.
• ECG Findings: Shortened QT interval, widening of the T wave, and bradycardia.
• Management: Aggressive volume expansion with 0.9% Normal Saline at 1.5 to 2 times maintenance to expand intravascular volume and promote renal calcium excretion (calciuresis). Once volume is restored, administer furosemide (a loop diuretic that inhibits calcium reabsorption; avoid thiazide diuretics, which increase renal calcium reabsorption). Severe or refractory cases are treated with IV bisphosphonates (pamidronate) or calcitonin.

Source check

RCH electrolyte guidelines, checked October 18, 2026. Verify product, age, indication, dose limits, and the applicable institutional order before clinical administration.