Treatment of Hypernatremia
The treatment of hypernatremia depends on the underlying volume status: hypovolemic hypernatremia requires hypotonic fluid replacement to correct free water deficit, euvolemic hypernatremia (typically from diabetes insipidus) needs addressing the underlying cause with possible desmopressin, and hypervolemic hypernatremia requires discontinuation of IV fluids and free water restriction. 1, 2
Initial Assessment and Classification
Before initiating treatment, determine the patient's volume status and measure serum electrolytes, acid-base status, fluid balance, hematocrit, and blood urea nitrogen to guide therapy 2. The three categories are:
- Hypovolemic hypernatremia: Water loss exceeds sodium loss 2
- Euvolemic hypernatremia: Often from diabetes insipidus (central or nephrogenic) 3
- Hypervolemic hypernatremia: Excess sodium relative to water 3
Treatment by Volume Status
Hypovolemic Hypernatremia
Administer hypotonic fluids to replace the free water deficit 1. The American Society of Nephrology specifically recommends avoiding isotonic saline as initial therapy, particularly in patients with nephrogenic diabetes insipidus 1. Calculate the free water deficit and replace with hypotonic solutions (0.45% saline or 5% dextrose in water) 4, 3.
Euvolemic Hypernatremia
- For diabetes insipidus: Distinguish between central (neurogenic) and nephrogenic forms 3
- Central diabetes insipidus: Treat with desmopressin (Minirin) 5
- Nephrogenic diabetes insipidus: Consider a low salt diet (<6 g/day) and protein restriction (<1 g/kg/day), along with thiazide diuretics 2
- Address underlying causes such as medications (lithium), hypokalemia, or hypercalcemia 3
Hypervolemic Hypernatremia
Discontinue intravenous fluid therapy and implement free water restriction 1. In cirrhotic patients, evaluate for the underlying cause and focus on achieving negative water balance 1. For heart failure patients with persistent severe hypernatremia and cognitive symptoms, vasopressin antagonists (tolvaptan or conivaptan) may be considered for short-term use 1, 2.
Rate of Correction: Critical Safety Consideration
The correction rate must be carefully controlled to prevent cerebral edema and neurological complications 2:
- Chronic hypernatremia (>48 hours): Correct at 10-15 mmol/L per 24 hours, not exceeding 0.4 mmol/L per hour 2, 3, 5
- Acute hypernatremia (<24 hours): Can be corrected more rapidly, though hemodialysis may be considered for severe cases 5
- Never exceed 8-10 mmol/L per day in chronic cases to avoid osmotic demyelination syndrome 5
Common Pitfall to Avoid
Correcting chronic hypernatremia too rapidly leads to cerebral edema, seizures, and potentially fatal neurological injury 1, 2. This is the opposite problem of hyponatremia correction, where rapid correction causes osmotic demyelination. With hypernatremia, rapid correction causes brain swelling as water shifts into previously dehydrated brain cells 1.
Monitoring During Treatment
Frequent laboratory monitoring is essential during correction 5:
- Check serum sodium every 2-4 hours initially when using hypotonic fluids 4
- Monitor serum potassium, chloride, and bicarbonate levels regularly 1
- Assess renal function and urine osmolality 1
- Adjust fluid replacement rates based on serial sodium measurements 6
Calculating Fluid Replacement
The water deficit should be calculated and replaced over 48-72 hours for chronic hypernatremia 6. Account for three components 6:
- Free water deficit: Based on current sodium level and body water
- Ongoing water losses: From urine, drains, or other sources
- Insensible losses: Approximately 500-1000 mL/day 6
Special Considerations
When initiating renal replacement therapy in patients with chronic hypernatremia, be cautious of rapid sodium drops during dialysis 5. In cirrhotic patients specifically, avoid rapid correction to prevent central pontine myelinolysis 2. For heart failure patients, sodium and fluid restriction with limitation to around 2 L/day is recommended, with stricter restriction for diuretic-resistant or significantly hypernatremic patients 1.