Management of Hypernatremia
Hypernatremia requires prompt correction with hypotonic fluids at a controlled rate, with the specific approach determined by volume status, chronicity, and underlying cause.
Initial Assessment and Diagnostic Approach
Determine the chronicity of hypernatremia (acute <24-48 hours vs. chronic >48 hours), as this fundamentally changes correction rates and risk profiles 1, 2. Acute hypernatremia can be corrected more rapidly, while chronic cases require slower correction to prevent cerebral edema 2.
Assess volume status through physical examination:
- Hypovolemic signs: orthostatic hypotension, tachycardia, dry mucous membranes, decreased skin turgor, flat neck veins 3
- Hypervolemic signs: peripheral edema, jugular venous distention, pulmonary congestion 3
- Euvolemic: normal volume status with intact thirst mechanism failure or water access issues 1
Obtain key laboratory studies:
- Serum glucose to exclude pseudohypernatremia (correct sodium by adding 1.6 mEq/L for each 100 mg/dL glucose >100 mg/dL) 3
- Urine osmolality and urine sodium to differentiate renal vs. extrarenal losses 1
- Urine volume to assess ongoing losses 1
- Serum osmolality (calculated as 2 × Na + BUN/2.8 + glucose/18) 3
Fluid Selection Based on Volume Status
Hypovolemic Hypernatremia
Administer hypotonic fluids such as 0.45% NaCl (half-normal saline) or 0.18% NaCl (quarter-normal saline) for moderate to severe hypernatremia 3. D5W (5% dextrose in water) is the preferred primary rehydration fluid because it delivers no renal osmotic load and allows controlled decrease in plasma osmolality 3.
Avoid isotonic saline (0.9% NaCl) in hypernatremic dehydration as it delivers excessive osmotic load, requiring 3 liters of urine to excrete the osmotic load from just 1 liter of isotonic fluid, which risks worsening hypernatremia 3.
Hypervolemic Hypernatremia
Use hypotonic infusions in conjunction with diuretics for hypervolemic hypernatremia, which occurs almost exclusively in ICU patients often due to infusion of hypertonic solutions 4. Great emphasis should be placed on prevention and the infusion of hypertonic solutions should be avoided 4.
Euvolemic Hypernatremia
Provide oral free water if the patient can tolerate it, or intravenous hypotonic fluids (D5W or 0.45% NaCl) if oral intake is not possible 5, 1.
Correction Rate Guidelines
For chronic hypernatremia (>48 hours), do not reduce sodium by more than 8-10 mmol/L per day to avoid osmotic demyelination syndrome 2. The maximum sodium reduction should be 10-15 mEq/L per 24 hours 6.
For acute hypernatremia (<24 hours), hemodialysis is an effective option to rapidly normalize serum sodium levels 2. However, when starting renal replacement therapy in patients with chronic hypernatremia, avoid a rapid drop in sodium concentration 2.
Fluid Administration Rates
For children, calculate initial fluid administration rate based on physiological maintenance requirements:
- 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 3
For adults, the initial fluid administration rate is 25-30 mL/kg/24 hours 3.
Special Populations
Nephrogenic Diabetes Insipidus
Patients with renal concentrating defects require ongoing hypotonic fluid administration to match excessive free water losses 3. Isotonic fluids should be avoided as they worsen hypernatremia in patients unable to excrete free water appropriately 3.
High-Risk Populations
Infants and malnourished patients may benefit from smaller-volume, frequent boluses (10 mL/kg) due to reduced cardiac output capacity 3.
Monitoring Protocol
Monitor serum sodium every 2-4 hours during initial titration 6. Adjust treatment by 10-20 mL/hr increments based on trend 6.
Monitor for complications including:
Underlying Cause Management
Address the root cause simultaneously:
- Excessive water loss (diarrhea, vomiting): replace ongoing losses 3
- Inadequate fluid intake: ensure access to free water 3
- Diabetes insipidus: consider desmopressin (Minirin) application 2
Critical Pitfalls to Avoid
Never correct chronic hypernatremia faster than 8-10 mmol/L per day as rapid changes in serum sodium concentration may cause osmotic demyelination syndrome 2.
Do not use isotonic saline in hypernatremic dehydration as it worsens the osmotic burden 3.
In patients with heart failure or volume overload, use 3% saline cautiously as it may worsen fluid retention despite the osmotic effect 6.
Close laboratory controls are essential throughout the correction process 2.