Why is dextrose (5% dextrose in water) administered in cases of hypernatremia (elevated sodium levels)?

Dextrose Administration for Hypernatremia: Mechanism and Rationale

5% dextrose in water (D5W) is the preferred fluid for treating hypernatremia because it provides free water without sodium, allowing for correction of elevated sodium levels while avoiding additional osmotic load that would worsen the condition. 1

Mechanism of Action

Dextrose in water works through several mechanisms to correct hypernatremia:

1. Free Water Provision:

   • D5W effectively provides free water once the dextrose is metabolized
   • After metabolism, D5W becomes hypotonic relative to plasma, allowing water to move into cells and dilute elevated sodium concentrations

2. Avoidance of Additional Sodium Load:

   • Unlike normal saline (0.9% NaCl), D5W contains no sodium
   • Salt-containing solutions would increase renal osmotic load, potentially worsening hypernatremia 1

3. Osmotic Considerations:

   • In conditions like nephrogenic diabetes insipidus (NDI), the tonicity of isotonic fluids (300 mOsm/kg) exceeds typical urine osmolality (100 mOsm/kg) by about 3-fold
   • This means approximately 3L of urine would be needed to excrete the osmotic load from 1L of isotonic fluid, risking worsening hypernatremia 1

Clinical Application

When to Use D5W for Hypernatremia

• Emergency management of hypernatremic dehydration 1
• Patients with nephrogenic diabetes insipidus 1
• Hypernatremia associated with hyperglycemic conditions 2
• Correction of hypernatremia in patients with impaired thirst mechanisms 3

Administration Guidelines

• Initial Rate: Calculate based on physiological demand

  • For children: First 10kg: 100ml/kg/24h; 10-20kg: 50ml/kg/24h; remaining: 20ml/kg/24h
  • For adults: 25-30ml/kg/24h 1

• Correction Rate: Sodium correction should not exceed 8 mEq/L in 24 hours to prevent osmotic demyelination syndrome 4

  • Target increasing serum sodium by 4-6 mEq/L in first few hours
  • For severe hypernatremia, target sodium levels should not exceed 123 mEq/L in first 24 hours 4

Monitoring Requirements

• Serum sodium every 2-4 hours initially, then every 4-6 hours once stabilized
• Vital signs every 1-2 hours initially
• Daily renal function tests and electrolytes with each sodium check 4

Special Considerations

Hypernatremia in Specific Conditions

1. Hyperglycemic States:

   • In diabetic ketoacidosis or hyperglycemic hyperosmolar state with hypernatremia, D5W helps correct both hyperglycemia and hypernatremia 2
   • When plasma glucose reaches 250-300 mg/dl during insulin therapy, adding 5-10% dextrose helps prevent hypoglycemia while continuing to correct sodium levels 1

2. Renal Replacement Therapy:

   • For patients on continuous renal replacement therapy with hypernatremia, calculated amounts of D5W can be administered prefilter to prevent overcorrection 5

3. Volume Status Assessment:

   • Assess volume status (hypovolemic, euvolemic, or hypervolemic) before treatment 4
   • In hypovolemic hypernatremia, initial fluid resuscitation may be needed before D5W administration

Cautions and Pitfalls

1. Avoid Rapid Correction:

   • Too rapid correction of hypernatremia can lead to cerebral edema 6
   • In cases of salt intoxication, diuretics may be needed in addition to slow water replacement 6

2. Monitor for Rebound Hypoglycemia:

   • Rebound hypoglycemia may occur in tube-fed patients if feeding is stopped abruptly, especially if on antidiabetic therapy 1

3. Avoid Salt-Containing Solutions:

   • NaCl 0.9% solutions should be avoided in hypernatremia treatment as they increase renal osmotic load 1
   • In cases where some sodium is needed, 0.2% sodium chloride in 5% dextrose may be considered for specific conditions 7

By understanding these principles, clinicians can effectively use dextrose solutions to safely correct hypernatremia while minimizing risks of complications such as cerebral edema or osmotic demyelination syndrome.