What are the root causes of hypernatremia?

Root Causes of Hypernatremia

Hypernatremia (serum sodium >145 mmol/L) is primarily caused by either inadequate water intake, excessive water loss, or excessive sodium intake, with inadequate water intake being the most common etiology in clinical practice. 1, 2

Pathophysiologic Classification

1. Water Deficit (Most Common)

• Decreased water intake:

  • Impaired thirst mechanism
  • Limited access to water (common in hospitalized, elderly, or disabled patients)
  • Altered mental status preventing water consumption
  • Iatrogenic (inadequate fluid prescription in hospitalized patients) 3

• Increased water loss:

  • Renal losses:

    • Diabetes insipidus (central or nephrogenic)
    • Osmotic diuresis (hyperglycemia, mannitol)
    • Polyuric phase of acute tubular necrosis
    • Diuretic use (especially loop diuretics)

  • Extrarenal losses:

    • Gastrointestinal losses (vomiting, diarrhea)
    • Respiratory losses (tachypnea, mechanical ventilation)
    • Skin losses (fever, burns, excessive sweating)
    • High output enterostomies 1

2. Sodium Gain (Less Common)

• Iatrogenic sodium administration (excessive sodium in IV fluids)
• Excessive sodium bicarbonate administration
• Hypertonic saline administration
• Ingestion of high sodium substances (salt tablets, seawater)
• Primary hyperaldosteronism

Special Considerations in Pediatric Patients

In neonates and very low birth weight infants (VLBWI), hypernatremia is often iatrogenic and results from 1:

• Incorrect replacement of transepidermal water loss (TEWL)
• Inadequate water intake
• Excessive sodium intake during the transition phase

Clinical Manifestations

Symptoms of hypernatremia primarily reflect neurologic dysfunction due to cellular dehydration and brain cell shrinkage:

• Mild: Thirst, lethargy, irritability, weakness
• Moderate: Confusion, altered mental status, muscle twitching
• Severe: Seizures, coma, intracranial hemorrhage, death

Diagnostic Approach

1. Confirm hypernatremia (serum sodium >145 mmol/L)

2. Assess volume status:

   • Hypovolemic: Signs of dehydration (tachycardia, hypotension, dry mucous membranes)
   • Euvolemic: Normal vital signs without edema
   • Hypervolemic: Edema, ascites, elevated blood pressure

3. Laboratory evaluation:

   • Serum electrolytes, BUN, creatinine
   • Urine osmolality and sodium
   • Plasma osmolality
   • Blood glucose

Treatment Principles

The treatment of hypernatremia must be approached carefully as rapid correction can lead to cerebral edema, seizures, and neurological injury 1.

Key treatment principles:

1. Identify and address the underlying cause
2. Replace water deficit gradually
3. Monitor serum sodium frequently during correction
4. Aim for sodium reduction rate of 10-15 mmol/L/24h 1

Pitfalls to Avoid

1. Overly rapid correction: Can lead to cerebral edema, seizures, and neurological damage
2. Inadequate diagnosis of underlying cause: May lead to recurrence
3. Failure to monitor electrolytes during correction: Can miss developing complications
4. Inadequate fluid prescription in hospitalized patients: A preventable cause of hospital-acquired hypernatremia 3
5. Overlooking ongoing fluid losses: May result in inadequate replacement

Prevention

In hospitalized patients, particularly pediatric patients:

• Careful monitoring of fluid balance
• Regular assessment of electrolytes
• Appropriate fluid prescription based on patient needs
• Special attention to patients with impaired thirst or limited access to water

Understanding the root causes of hypernatremia is essential for proper diagnosis, treatment, and prevention of this potentially life-threatening electrolyte disorder.