What are the causes and effects of hypernatremia?

Hypernatremia Causes

Hypernatremia is predominantly caused by excessive water loss rather than sodium excess, with inadequate water intake and iatrogenic sodium administration being important but less common mechanisms. 1

Primary Mechanisms

Excessive Water Loss (Most Common)

• Transepidermal water loss is a major route, particularly in very low birth weight infants and patients with severe burns 1
• Gastrointestinal losses from diarrhea, vomiting, or nasogastric drainage contribute significantly 1, 2
• Renal water losses occur through:
  • Nephrogenic diabetes insipidus 1
  • Central diabetes insipidus (particularly post-neurosurgery or traumatic brain injury) 1
  • Osmotic diuresis from hyperglycemia or excessive solute load 3, 4
• Severe burns cause massive insensible water losses through damaged skin 1

Inadequate Water Intake

• Impaired thirst mechanism in elderly or neurologically impaired patients 3
• Lack of access to water in bedridden, hospitalized, or institutionalized patients 1, 3
• Impaired consciousness preventing self-hydration 5

Primary Sodium Excess (Uncommon but Iatrogenic)

• Excessive sodium administration during parenteral nutrition, especially in neonates 1
• Hypertonic saline administration in patients with underlying renal concentrating defects 1
• Incorrect formula preparation with excessive solute load in infants 4

Context-Specific Causes

Neonatal Hypernatremia

• Iatrogenic causes dominate: incorrect replacement of transepidermal water loss and inadequate water intake relative to insensible losses 1
• Excessive sodium intake through parenteral nutrition is particularly problematic in premature infants 1

Neurosurgical Patients

• Transient central diabetes insipidus following neurosurgery or traumatic brain injury 1
• This represents a distinct population requiring specific monitoring 1

Critical Pitfall to Avoid

Administering isotonic maintenance fluids to patients with significant renal concentrating defects (such as nephrogenic diabetes insipidus) will cause or worsen hypernatremia—hypotonic fluid replacement is mandatory in these patients. 1

Clinical Effects and Morbidity

Central Nervous System Dysfunction

• Hypernatremic dehydration carries high morbidity and mortality, primarily from CNS dysfunction including confusion, coma, and seizures 1, 5, 6
• Symptoms depend on the rate of development: rapid onset causes more severe neurological manifestations 4
• Pronounced thirst in awake patients is characteristic 5

Correction-Related Complications

• Rapid correction poses additional risk for cerebral edema, increased intracranial pressure, stupor, and convulsions 4
• Recommended reduction rate is 10-15 mmol/L per 24 hours for established hypernatremia (>48 hours duration) 1, 5
• Osmotic demyelination syndrome can occur with overly rapid correction 5

Long-Term Sequelae

• Approximately 10-15% of children with serum sodium ≥160 mEq/L will have permanent neurological deficits 4
• Even with appropriate management, CNS damage can result either from the hypernatremia itself or from correction errors 6