What causes hypernatremia in patients?

Causes of Hypernatremia in Hospitalized Patients

The most common causes of hypernatremia in hospitalized patients are inadequate fluid prescription, overlooked ongoing fluid losses, and impaired access to water, particularly in elderly patients, those with altered mental status, and critically ill patients. 1

Classification by Volume Status

Hypernatremia (serum sodium >145 mmol/L) can be categorized based on volume status:

1. Hypovolemic Hypernatremia

• Water and sodium losses with greater water than sodium loss:
  • Gastrointestinal losses: diarrhea, vomiting
  • Excessive sweating
  • Burns
  • Osmotic diuresis (e.g., uncontrolled diabetes)
  • Renal losses (diuretic use, especially in cirrhotic patients) 1, 2

2. Euvolemic Hypernatremia

• Pure water loss without significant sodium loss:
  • Diabetes insipidus (central or nephrogenic)
    • Nephrogenic diabetes insipidus: kidney resistance to ADH action 1
    • Central diabetes insipidus: inadequate ADH secretion
  • Insensible losses (fever, mechanical ventilation, tachypnea)
  • Inadequate water intake in patients with:
    • Impaired thirst mechanism
    • Altered mental status
    • Physical inability to access water 1, 2, 3

3. Hypervolemic Hypernatremia

• Sodium gain exceeding water gain:
  • Iatrogenic sodium administration:
    • Hypertonic saline
    • Sodium bicarbonate
    • High sodium-containing medications
  • Parenteral nutrition with inadequate free water 1, 4

High-Risk Patient Populations

• Elderly patients: Decreased thirst sensation and impaired renal concentrating ability 1, 3
• Infants: Unable to communicate thirst or access water independently 1
• Critically ill patients: Multiple risk factors including:
  • Mechanical ventilation (increased insensible losses)
  • Altered mental status
  • Inability to communicate thirst
  • Multiple medications affecting water/sodium balance 1, 2
• Neurological disorders: Impaired thirst center function or inability to communicate thirst 1

Hospital-Specific Risk Factors

• Inadequate fluid prescription: Not accounting for all ongoing losses 1
• Overlooked fluid losses: Failure to monitor and replace ongoing losses 1
• Excessive diuretic use: Particularly in cirrhotic patients 1
• Parenteral nutrition: Improper electrolyte composition or inadequate free water 1
• Improper monitoring: Failure to regularly assess electrolytes in high-risk patients 1, 3

Diagnostic Approach

When evaluating hypernatremia in hospitalized patients, follow these steps:

1. Confirm true hypernatremia (exclude pseudohypernatremia)
2. Determine volume status (hypovolemic, euvolemic, hypervolemic)
3. Measure urine sodium and osmolality
4. Assess ongoing urinary electrolyte free water clearance
5. Evaluate for other electrolyte disorders 3

Clinical Pearls and Pitfalls

• Pitfall: Focusing only on sodium correction without identifying the underlying cause can lead to recurrence
• Pitfall: Rapid correction of chronic hypernatremia (>48 hours) can cause cerebral edema, seizures, and neurological injury 1
• Pearl: Target sodium reduction rate should be 8-10 mmol/L/day for chronic hypernatremia 1
• Pearl: Regular assessment of electrolytes is crucial in patients receiving parenteral nutrition or diuretics 1

Hypernatremia in hospitalized patients is often preventable with careful attention to fluid balance, regular electrolyte monitoring, and ensuring adequate water access for at-risk patients. Prompt identification and correction of the underlying cause is essential to reduce morbidity and mortality.