Management of Symptomatic Hypernatremia
For symptomatic hypernatremia, correct the sodium deficit using hypotonic fluids (5% dextrose or 0.45% NaCl) at a maximum rate of 0.4 mmol/L per hour or 10 mmol/L per 24 hours to prevent cerebral edema, while simultaneously addressing the underlying cause. 1, 2
Initial Assessment and Diagnosis
Determine the acuity and severity of hypernatremia to guide correction rates 1, 2:
- Acute hypernatremia (<24-48 hours): Can be corrected more rapidly without significant risk of cerebral edema 1, 3
- Chronic hypernatremia (>48 hours): Requires slower correction to prevent osmotic complications 1, 2
Assess volume status and urine osmolality to identify the underlying cause 1, 2:
- Hypervolemic: Excessive sodium intake (hypertonic saline, sodium bicarbonate) or primary hyperaldosteronism 2
- Euvolemic: Diabetes insipidus (central or nephrogenic) 2
- Hypovolemic: Renal or extrarenal water losses 2
Fluid Selection and Correction Strategy
Primary fluid choice is 5% dextrose (D5W) as it delivers no renal osmotic load and allows controlled decrease in plasma osmolality 4. Alternative is 0.45% NaCl (half-normal saline) for moderate hypernatremia 4.
Critical correction rate limits 1, 2:
- Maximum 0.4 mmol/L per hour
- Maximum 8-10 mmol/L per 24 hours for chronic hypernatremia
- Slower correction (0.5 mmol/L per hour maximum) is safer for established hypernatremia
Avoid isotonic saline (0.9% NaCl) in hypernatremic patients as it delivers excessive osmotic load, requiring 3 liters of urine to excrete the osmotic load from just 1 liter of fluid, which risks worsening hypernatremia 4.
Initial Fluid Administration Rates
Calculate maintenance fluid requirements 4:
- Adults: 25-30 mL/kg per 24 hours
- Children: 100 mL/kg/24h for first 10 kg, 50 mL/kg/24h for 10-20 kg, 20 mL/kg/24h for remaining weight
Treatment Based on Underlying Cause
For diabetes insipidus (central): Administer desmopressin (Minirin) in addition to hypotonic fluid replacement 1.
For nephrogenic diabetes insipidus: Ongoing hypotonic fluid administration is required to match excessive free water losses; isotonic fluids must be avoided as they worsen hypernatremia 4.
For hypervolemic hypernatremia: Address excessive sodium intake and consider treating underlying conditions like primary hyperaldosteronism 2.
Special Considerations and Monitoring
**Acute hypernatremia (<24 hours)**: Recent evidence suggests rapid correction may be safe in critically ill patients, with no increased mortality or cerebral edema risk even with correction rates >0.5 mmol/L per hour 3. However, hemodialysis is an effective option for rapid normalization if needed 1.
High-risk populations: Infants and malnourished patients may benefit from smaller-volume, frequent boluses (10 mL/kg) due to reduced cardiac output capacity 4.
Critical monitoring: Close laboratory controls of serum sodium are essential during correction 1. Check sodium levels every 2-4 hours initially to ensure correction rate remains within safe limits.
Common Pitfalls to Avoid
- Never use isotonic fluids in hypernatremic patients with renal concentrating defects - this will worsen hypernatremia 4
- Avoid overly rapid correction of chronic hypernatremia - exceeding 10 mmol/L per 24 hours risks cerebral edema, though recent data suggests this may be less dangerous than previously thought 1, 3
- Do not start renal replacement therapy without considering sodium correction rate - rapid drops in sodium concentration must be avoided even when initiating dialysis in chronic hypernatremia 1