Free Water Flush for Hypernatremia Correction
For correcting hypernatremia, use hypotonic fluids such as 0.45% NaCl (half-normal saline), 0.18% NaCl (quarter-normal saline), or D5W (5% dextrose in water) to provide free water replacement. The specific choice depends on the severity of hypernatremia and clinical context 1.
Hypotonic Fluid Options
Primary fluid choices for hypernatremia correction:
- 0.45% NaCl (half-normal saline): Contains 77 mEq/L sodium with osmolarity ~154 mOsm/L, appropriate for moderate hypernatremia correction 1
- 0.18% NaCl (quarter-normal saline): Contains ~31 mEq/L sodium, providing more aggressive free water replacement for severe cases 1
- D5W (5% dextrose in water): Delivers no renal osmotic load and allows slow, controlled decrease in plasma osmolality—this is the preferred choice for primary rehydration 1
Critical Safety Considerations
Never use isotonic saline (0.9% NaCl) as initial therapy for hypernatremia, as it will worsen the condition 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 must not exceed 10-15 mmol/L per 24 hours to prevent cerebral edema, seizures, and permanent neurological injury 1, 2. For chronic hypernatremia (>48 hours duration), slower correction is critical because brain cells synthesize intracellular osmolytes to adapt to hyperosmolar conditions 1.
Special Clinical Scenarios
For nephrogenic diabetes insipidus: Ongoing hypotonic fluid administration is required to match excessive free water losses 1. Isotonic fluids are absolutely contraindicated as they will cause or worsen hypernatremia in these patients 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 3, 1.
For patients with renal concentrating defects: Hypotonic fluid replacement is essential to prevent hypernatremia, as these patients cannot concentrate urine appropriately 3.
Initial Fluid Administration Rates
- Children: 100 mL/kg/24 hours for first 10 kg, 50 mL/kg/24 hours for 10-20 kg, and 20 mL/kg/24 hours for remaining weight 1
- Adults: 25-30 mL/kg/24 hours 1
Common Pitfalls to Avoid
- Avoid isotonic saline in hypernatremia: This exacerbates the condition, especially in patients with nephrogenic diabetes insipidus or renal concentrating defects 1
- Do not correct too rapidly: Correcting chronic hypernatremia faster than 10-15 mmol/L per 24 hours can lead to cerebral edema and seizures 1, 2
- Monitor high-risk populations closely: Infants and malnourished patients may benefit from smaller-volume, frequent boluses (10 mL/kg) due to reduced cardiac output capacity 1