Increasing Free Water Intake to Correct Hypernatremia
For hypernatremia correction, administer hypotonic fluids such as 0.45% NaCl, 0.18% NaCl, or D5W (5% dextrose in water) to replace free water deficit, with D5W preferred as it delivers no renal osmotic load and allows controlled decrease in plasma osmolality. 1
Fluid Selection Strategy
Primary hypotonic fluid options include:
- D5W (5% dextrose in water) is the preferred choice because it provides pure free water without any osmotic load, allowing the most controlled correction 1
- 0.45% NaCl (half-normal saline) contains 77 mEq/L sodium with osmolarity ~154 mOsm/L, appropriate for moderate hypernatremia 1
- 0.18% NaCl (quarter-normal saline) contains ~31 mEq/L sodium, providing more aggressive free water replacement for severe cases 1
Never use isotonic saline (0.9% NaCl) as initial therapy—it will worsen hypernatremia, especially in patients with nephrogenic diabetes insipidus or renal concentrating defects. 1 Isotonic saline delivers excessive osmotic load, requiring 3 liters of urine to excrete the osmotic load from just 1 liter of fluid, which risks worsening hypernatremia 1
Correction Rate Guidelines
The maximum correction rate should be 10-15 mmol/L per 24 hours for chronic hypernatremia (>48 hours duration) to prevent cerebral edema. 1 Correcting chronic hypernatremia too rapidly can lead to cerebral edema, seizures, and permanent neurological injury because brain cells synthesize intracellular osmolytes over 48 hours to adapt to hyperosmolar conditions 1
For acute hypernatremia (<24-48 hours), correction can proceed more rapidly, up to 1 mmol/L/hour if severely symptomatic 1
Initial Fluid Administration Rates
For adults: Start with 25-30 mL/kg/24 hours of hypotonic fluid 1
For children: Calculate based on physiological maintenance requirements 1:
- 100 mL/kg/24 hours for the first 10 kg
- 50 mL/kg/24 hours for 10-20 kg
- 20 mL/kg/24 hours for remaining weight
Special Clinical Scenarios
For severe hypernatremia with altered mental status: Combine IV hypotonic fluids with free water via nasogastric tube, targeting correction of 10-15 mmol/L per 24 hours 1 This approach was successfully used in a case of severe hypernatremia (>190 mEq/L corrected) where dextrose 5% in water, ringer's lactate, free water via NG tube, and IV desmopressin improved serum sodium to 140 mEq/L 2
For nephrogenic diabetes insipidus: Ongoing hypotonic fluid administration is required to match excessive free water losses 1 These patients have impaired renal concentrating ability and will worsen with isotonic fluids 1
For severe burns or voluminous diarrhea: Hypotonic fluids are required to keep up with ongoing free water losses, with fluid composition matched to losses while providing adequate free water 1
Monitoring Requirements
- Assess clinical status including neurological symptoms, vital signs, and volume status 1
- Measure blood electrolyte concentrations and acid-base status regularly 1
- Calculate fluid and electrolyte balance 1
- Check hematocrit and blood urea nitrogen to assess hydration status 1
- Monitor serum sodium, potassium, chloride, and bicarbonate levels during treatment 1
- Assess renal function and urine osmolality 1
Critical Pitfalls to Avoid
Never correct chronic hypernatremia faster than 10-15 mmol/L per 24 hours—rapid correction causes cerebral edema and permanent neurological damage 1
Avoid isotonic saline in hypernatremia—it worsens the condition by delivering excessive sodium without adequate free water 1
Do not use prolonged induced hypernatremia to control intracranial pressure in traumatic brain injury—it requires an intact blood-brain barrier to be effective and may worsen cerebral contusions 1