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AKA: hypernatraemia

Evaluation and management of high blood sodium in pediatric patients


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Free water deficit

  • Decreased access to free water
    • Young children
    • Altered mental status
      • Sedation
      • Coma
    • Mechanical ventilation (e.g., intubation)
    • Immobilization, restraints
    • Impaired thirst
    • Impaired intake
      • Breastfeeding infants
  • Hypotonic fluid losses
    • Kidney losses
      • Diuretics (loop, thiazide)
      • Osmotic diuresis
        • Hyperglycemia (e.g., uncontrolled diabetes)
        • Mannitol
      • Post-AKI diuresis (recovery from acute tubular necrosis)
      • Postobstructive diuresis
        • Obstructive uropathy
    • GI
      • Diarrhea
        • Laxative/cathartic use/abuse (e.g., lactulose)
      • Nasogastric suction
      • Drains/fistulas/ostomies
    • Respiratory tract
    • Skin (burns)
    • Fever
      • Impaired urinary concentrating ability
        • Kidney dysplasia
        • Medullary cystic kidney disease
        • Polycystic kidney disease (PKD)
        • Tubulointerstitial disease
        • Diabetes insipidus (DI)

          • Central: ↑ ADH production (arginine vasopressin deficiency, AVP-D)
          • Nephrogenic: ↓ responsiveness to ADH (arginine vasopressin resistance, AVP-R)
    • Transient water shifts
      • Occurs in setting of seizures, intense exercise
      • Resolves within 15 minutes

Sodium gain

  • Salt poisoning (very rare)
    • Incorrect formula preparation
  • Iatrogenic causes
    • Hypertonic electrolyte solutions
      • Sodium bicarbonate (e.g., during resuscitation)
      • Hypertonic saline
    • Sodium ingestion
      • NaCl tablets
    • Sodium modeling in

Signs and symptoms

  • Acute (<48 hours) hypernatremia may be symptomatic, particularly when severe

  • Chronic (≥48 hours) hypernatremia is more often asymptomatic

    • More likely to occur in children with neurological abnormalities, making it difficult to distinguish which symptoms are attributable to hypernatremia
  • Increased thirst

  • Increased muscle tone

  • Muscle twitching

  • Nystagmus

  • Irritability

  • Restlessness

  • Seizures

  • Fever

  • Tachypnea

  • Rhabdomyolysis

  • Most often due to hypovolemia

    • Delayed capillary refill
    • Dry mucous membranes
    • Hypotension
    • Oliguria/anuria
    • Orthostasis
    • Tachycardia
  • Altered mental status, lethargy that may progress to coma, seizures

    • Seen in acute, severe hypernatremia
  • Vascular rupture cerebral/subarachnoid hemorrhage, irreversible neuronal injury

    • Only in extreme cases (e.g., salt poisoning)


  • Careful assessment of volume status
    • Weight loss more suggestive of Hypovolemia
  • Weight gain may be seen in salt poisoning
  • Laboratory evaluation
    • BUN, creatinine
    • Plasma and urine osmolality
      • Confirms true hypertonic hypernatremia
        • Spurious hypernatremia is rare, but has been documented in hypoalbuminemic neonates when using indirect ion-selective electrodes (as is typically used in main laboratory analyzers)
      • Comparison of plasma vs urine osmolality is helpful in establishing diagnosis
        • If uOsm < pOsm, urinary concentrating defect is present
          • Water deprivation test to establish etiology
        • if uOsm > pOsm, urinary concentrating ability is intact and non-kidney causes should be considered
    • FeNa
      • >2% in hydrated patient suggests salt poisoning
      • <1% suggestive of dehydration from water loss
      • Note that premature neonatal kidneys may only absorb 85-95% of filtered sodium, so a FeNa of ≤5% would suggest sodium retention in that setting
        • Premature infants tend to remain in negative sodium balance for the first 2-3 weeks of life, and FeNa is higher in those with sepsis or respiratory disease
    • Consider aldosterone, cortisol, ADH (copeptin proAVP), ACTH level
  • Distinguish polyuria from solute diuresis


  • Depends upon the cause, chronicity, and clinical status of the patient

Restore intravascular volume if necessary

  • Hypernatremia in children is typically associated with hypovolemia, in which cause there is a need to restore both water and electrolyte status
    • If clinically significant hypovolemia present, fluid resuscitation is the priority
      • Bolus with 20-60 mL/kg of 0.9% (normal) saline

Determine free water deficit

  • Calculator the free water deficit using one of the following equations:
    • Free water deficit (in mL) = Current total body water (TBW, in mL) x ([current plasma Na/140] - 1)
    • Free water deficit (in mL) = 4 mL/kg x (weight in kg) x (desired change in plasma Na)
      • Based on the rule that 4 mL/kg of free water should lower sodium by 1 mEq/L
      • Desired change in plasma Na = (current Na) - (desired Na)

Choosing a strategy to restore free water

  • Rate: usually 8-12 mEq/L per 24 hours
    • Based on retrospective data showing cerebral edema was associated with a faster rate of correction
    • Emerging evidence suggests more rapid correction of hypernatremia is safe