What are the causes of hypernatremia?

Causes of Hypernatremia

Hypernatremia is most commonly caused by inadequate water intake, while other major causes include increased water losses (renal and extrarenal) and excessive sodium intake. 1

Classification of Hypernatremia by Mechanism

1. Inadequate Water Intake

• Most common etiology in clinical practice 1
• Particularly affects:
  • Elderly patients with impaired thirst mechanism
  • Infants who cannot communicate thirst
  • Patients with altered mental status
  • Patients without access to water
  • Individuals with neurological disorders affecting thirst perception 2, 3

2. Increased Water Loss

Renal Losses

• Diabetes insipidus:
  • Central (deficient ADH production)
  • Nephrogenic (kidney resistance to ADH)
• Osmotic diuresis: due to glucose, mannitol, urea
• Diuretic use: especially loop diuretics
• Renal diseases affecting concentrating ability 1, 4

Extrarenal Losses

• Gastrointestinal losses: diarrhea, vomiting, high output enterostomies
• Respiratory losses: increased with tachypnea, fever
• Skin losses:
  • Burns
  • Excessive sweating
  • Transepidermal water loss (especially in premature infants) 1, 3

3. Excessive Sodium Intake

• Iatrogenic causes:
  • Hypertonic saline administration
  • Sodium bicarbonate administration
  • Incorrect parenteral nutrition formulation
• Salt intoxication: accidental or intentional
• Excessive administration of sodium-containing medications 1, 5

Classification by Volume Status

1. Hypovolemic Hypernatremia

• Water and sodium loss, with proportionally greater water loss
• Causes: gastrointestinal losses, excessive sweating, burns, osmotic diuresis
• Clinical signs: dry mucous membranes, decreased skin turgor, orthostatic hypotension 1, 5

2. Euvolemic Hypernatremia

• Pure water loss or deficiency
• Causes: diabetes insipidus, inadequate water intake, insensible losses
• Clinical signs: normal volume status, thirst 3, 5

3. Hypervolemic Hypernatremia

• Excess sodium with some water gain
• Causes: excessive sodium administration, primary hyperaldosteronism
• Clinical signs: edema, hypertension 1, 5

High-Risk Populations

• Neonates and very low birth weight infants: vulnerable to incorrect replacement of transepidermal water loss 1
• Elderly patients: impaired thirst mechanism and access to water 2
• Critically ill patients: multiple risk factors including impaired access to water, increased losses, and iatrogenic causes 6
• Psychiatric patients: particularly those with major depressive disorder due to abnormalities in thirst sensation or reduced oral intake 6
• Cirrhotic patients: due to excessive diuretic use, gastrointestinal losses, or inadequate fluid replacement 1

Clinical Pearls and Pitfalls

• Hypernatremia is defined as serum sodium >145 mmol/L 1, 5
• Always assess volume status when evaluating hypernatremia, as it guides treatment approach 1
• Hospital-acquired hypernatremia is often preventable and related to inadequate fluid prescription or overlooking ongoing fluid losses 1
• Regular assessment of electrolytes is crucial in patients receiving parenteral nutrition or diuretics 1
• Symptoms primarily reflect neurologic dysfunction due to cellular dehydration and brain cell shrinkage, ranging from mild (thirst, lethargy) to severe (seizures, coma) 1