What are the causes of hypernatremia?

Causes of Hypernatremia

Hypernatremia (serum sodium >145 mmol/L) primarily results from water deficit relative to sodium content, occurring through inadequate water intake, excessive water loss, or rarely from excessive sodium intake. 1

Classification by Volume Status

1. Hypovolemic Hypernatremia

• Causes of water and sodium loss (with greater water than sodium loss):
  • Gastrointestinal losses: vomiting, diarrhea, fistulas 1, 2
  • Excessive sweating/fever 3
  • Renal losses: osmotic diuresis (e.g., glucose, mannitol), diuretic use (especially in cirrhotic patients) 1
  • Burns 4
  • Third-space losses 2

2. Euvolemic Hypernatremia

• Causes of pure water loss:
  • Diabetes insipidus 1, 5:
    • Central (inadequate ADH secretion)
    • Nephrogenic (kidney resistance to ADH action)
  • Insensible losses: respiratory, skin 2, 3
  • Inadequate water intake in patients with:
    • Altered mental status 1
    • Impaired thirst mechanism 3
    • Physical inability to access water 1
    • Infants and elderly (high-risk groups) 1

3. Hypervolemic Hypernatremia

• Causes of sodium gain exceeding water gain:
  • Iatrogenic: hypertonic saline administration, sodium bicarbonate excess 2, 5
  • Excessive sodium ingestion 6
  • Primary hyperaldosteronism 5
  • Cushing syndrome 5

Special Populations at Risk

• Critically ill patients are particularly vulnerable due to 1:

  • Mechanical ventilation
  • Increased insensible losses
  • Inability to communicate thirst
  • Administration of sodium-containing medications/fluids

• Hospitalized patients develop hypernatremia due to 1:

  • Inadequate fluid prescription
  • Overlooked ongoing fluid losses
  • Improper parenteral nutrition

• Neurological patients are at high risk due to 1:

  • Central diabetes insipidus following brain injury
  • Impaired thirst sensation
  • Physical inability to obtain water

Diagnostic Approach

The diagnostic approach to hypernatremia involves 2:

1. Excluding pseudohypernatremia
2. Confirming glucose-corrected sodium concentrations
3. Determining extracellular volume status (key for classification)
4. Measuring urine sodium levels and osmolality
5. Assessing arginine vasopressin/copeptin levels when appropriate

Common Pitfalls and Caveats

• Failure to recognize hypernatremia in patients with altered mental status, as confusion may be attributed to other causes 3
• Overlooking ongoing fluid losses in critically ill patients 1
• Rapid correction of chronic hypernatremia (>48h duration) can lead to cerebral edema and neurological injury; correction should not exceed 8-10 mmol/L/day 1, 6
• Misdiagnosis of diabetes insipidus types (central vs. nephrogenic) leading to inappropriate treatment 5
• Inadequate monitoring of patients receiving parenteral nutrition or diuretics 1

Understanding the underlying mechanism and volume status is crucial for proper diagnosis and management of hypernatremia, as it guides the approach to treatment and helps prevent complications.