What causes hypernatremia?

Hypernatremia Causes

Hypernatremia is predominantly caused by excessive water loss rather than sodium excess, with the most common mechanisms being gastrointestinal losses, renal water losses, transepidermal water loss, and inadequate water intake in patients with impaired access to fluids. 1, 2

Primary Mechanisms

Water Loss (Most Common)

• Gastrointestinal losses including diarrhea, vomiting, fistulas, and drainage tubes are frequent culprits 1
• Renal water losses occur in diabetes insipidus (both central and nephrogenic), with transient diabetes insipidus particularly common after neurosurgery or traumatic brain injury 2
• Transepidermal water loss is especially problematic in very low birth weight infants and patients with severe burns 2
• Excessive sweating in endurance athletes without adequate water replacement can precipitate hypernatremia 1

Inadequate Water Intake

• Impaired thirst mechanisms or lack of access to water in bedridden patients is a common cause, particularly in elderly or hospitalized individuals 2, 3
• This mechanism is often overlooked but represents a significant proportion of cases in vulnerable populations 3

Sodium Excess (Uncommon but Important)

• Iatrogenic sodium administration through parenteral nutrition, particularly in neonates, is an important preventable cause 1, 2
• Hypertonic saline administration in patients with underlying renal concentrating defects can worsen or cause hypernatremia 2
• Excessive salt ingestion is rare but can be fatal, with as little as 70-90 grams causing severe hypernatremia 4

Population-Specific Causes

Neonates and Infants

• Incorrect replacement of transepidermal water loss is the leading iatrogenic cause in very low birth weight infants 1, 2
• Inadequate water intake relative to insensible losses combined with excessive sodium in parenteral nutrition 2
• Hypernatremic dehydration in this population carries the highest morbidity and mortality, primarily from CNS dysfunction 5

Hospitalized Patients

• Inadequate fluid prescription is the most common iatrogenic cause in hospital settings 1
• Excessive diuretic use in patients with liver disease can cause hypovolemic hypernatremia 1

Neurosurgical Patients

• Central diabetes insipidus following neurosurgery or traumatic brain injury is a specific concern 2

Critical Pitfall to Avoid

Never administer isotonic maintenance fluids to patients with significant renal concentrating defects (such as nephrogenic diabetes insipidus), as this will cause or worsen hypernatremia; hypotonic fluid replacement is mandatory in these cases. 2

Diagnostic Clues

• Urine osmolality and sodium measurements help determine whether kidneys are appropriately concentrating urine and guide diagnosis 1
• Volume status assessment combined with medical history is essential for differential diagnosis 6
• The clinical presentation typically includes CNS dysfunction (confusion, delirium, coma) and pronounced thirst in awake patients 6

Associated Morbidity

Hypernatremic dehydration carries high morbidity and mortality rates, with approximately 10-15% of children with serum sodium ≥160 mEq/L developing permanent neurological deficits 7. The age of the patient and initial serum sodium concentration are the most important prognostic indicators, with very young patients and those with lesser degrees of hypernatremia having better survival rates 4.