Management of Hypernatremic Dehydration
For hypernatremic dehydration, use hypotonic fluids (5% dextrose or 0.45% NaCl) and correct slowly at no more than 0.4 mmol/L/hour (10 mmol/L per 24 hours) to prevent cerebral edema, with total correction typically over 48-72 hours depending on severity. 1, 2, 3
Immediate Assessment and Fluid Selection
Avoid isotonic saline (0.9% NaCl) in hypernatremic dehydration as it delivers excessive osmotic load—approximately 300 mOsm/kg H₂O compared to typical urine osmolality of ~100 mOsm/kg H₂O, requiring 3 liters of urine to excrete the osmotic load from just 1 liter of isotonic fluid, which risks worsening hypernatremia 1.
Preferred Fluid Choices:
- 5% dextrose (D5W) as the primary rehydration fluid because it delivers no renal osmotic load and allows slow, controlled decrease in plasma osmolality 1
- 0.45% NaCl (half-normal saline) containing 77 mEq/L sodium with osmolarity ~154 mOsm/L for moderate hypernatremia 4
- 0.18% NaCl (quarter-normal saline) with ~31 mEq/L sodium for more aggressive free water replacement in severe cases 4
Correction Rate Guidelines
Acute Hypernatremia (<48 hours):
- Rapid correction improves prognosis by preventing cellular dehydration effects 2
- Can correct more quickly without significant risk of cerebral edema 2
Chronic Hypernatremia (>48 hours):
- Maximum correction rate: 0.4 mmol/L/hour or 10 mmol/L per 24 hours 2, 3
- Slower correction over 48-72 hours is essential to prevent cerebral edema, seizures, and increased intracranial pressure 5, 6
- Too-rapid correction causes brain cells to swell as they have adapted to hyperosmolar conditions by increasing intracellular osmoles 5, 6
Initial Fluid Administration Rates
Calculate based on physiological maintenance requirements 1:
Children:
- First 10 kg: 100 mL/kg/24 hours
- 10-20 kg: 50 mL/kg/24 hours
- Remaining weight: 20 mL/kg/24 hours 1
Adults:
- 25-30 mL/kg/24 hours 1
Start at maintenance rate, which will result in slow plasma osmolality decrease when using 5% dextrose 1.
Monitoring Requirements
- Check serum sodium every 2-4 hours initially during active correction 3
- Monitor for signs of cerebral edema: altered mental status, seizures, increased intracranial pressure 5, 6
- Track intake/output meticulously 6
- Daily weights to assess hydration status 6
- Adjust fluid rate if correction is too rapid or too slow 3, 6
Special Considerations
Nephrogenic Diabetes Insipidus:
- These patients require ongoing hypotonic fluid administration to match excessive free water losses 4
- Isotonic fluids will worsen hypernatremia in patients with renal concentrating defects 4
- May need to withdraw diuretics and COX inhibitors during acute management 1
High-Risk Populations:
- Infants and malnourished patients may benefit from smaller-volume, frequent boluses (10 mL/kg) due to reduced cardiac output capacity 1
- Approximately 10-15% of children with serum sodium ≥160 mEq/L will have permanent neurological deficits despite appropriate management 6
Critical Pitfalls to Avoid
- Never use isotonic saline as primary rehydration fluid in hypernatremic dehydration—it paradoxically worsens hypernatremia 1
- Never correct chronic hypernatremia rapidly—this causes cerebral edema, seizures, stupor, and potentially fatal increased intracranial pressure 5, 6
- Never assume acute hypernatremia without clear history—default to slow correction if timing uncertain 2, 3
- Avoid correcting faster than 0.4 mmol/L/hour in chronic cases regardless of clinical improvement 2, 3
Underlying Cause Management
Address the precipitating factors concurrently 3: