What is the treatment for hypernatremia?

Treatment of Hypernatremia

Hypernatremia should be corrected with hypotonic fluids at a rate not exceeding 10-12 mmol/L per 24 hours for chronic cases (>48 hours), while acute hypernatremia (<24 hours) can be corrected more rapidly. 1, 2

Initial Assessment and Classification

• Determine the duration: Acute hypernatremia (<24-48 hours) vs. chronic hypernatremia (>48 hours), as this fundamentally changes your correction rate 1, 3
• Assess volume status: Identify whether the patient is hypovolemic (most common from water losses), euvolemic (diabetes insipidus), or hypervolemic (rare, from sodium excess) 3, 2
• Measure urine osmolality and sodium: Urine osmolality <300 mOsm/kg suggests diabetes insipidus; urine sodium helps distinguish renal from extrarenal losses 3, 2
• Check for diabetes insipidus: If urine is inappropriately dilute despite hypernatremia, measure arginine vasopressin or copeptin levels to differentiate central from nephrogenic diabetes insipidus 2

Correction Rate Guidelines

For chronic hypernatremia (>48 hours):

• Limit correction to 8-10 mmol/L per 24 hours to prevent cerebral edema from rapid osmotic shifts 1, 4
• Target a rate of 0.4 mmol/L per hour or less for gradual restoration of plasma tonicity 3
• Monitor serum sodium every 2-4 hours during active correction to prevent overcorrection 5

For acute hypernatremia (<24 hours):

• Rapid correction is safe and improves prognosis by preventing cellular dehydration 3
• Hemodialysis is an effective option for rapidly normalizing severe acute hypernatremia 1

Fluid Replacement Strategy

Calculate the free water deficit using:

• Free water deficit = 0.5 × body weight (kg) × [(current Na/140) - 1] 2
• Add ongoing losses (insensible losses typically 500-1000 mL/day, plus any measured losses) 2

Select appropriate replacement fluids:

• For hypovolemic hypernatremia: Start with 0.45% saline or 5% dextrose in water (D5W) 6, 3
• For euvolemic hypernatremia: Use hypotonic solutions like D5W or 0.45% saline 6, 3
• For hypervolemic hypernatremia: Address the underlying cause (stop sodium sources) and consider loop diuretics with hypotonic fluid replacement 3

Specific Etiologies and Targeted Treatment

Central diabetes insipidus:

• Administer desmopressin (DDAVP) 1-2 mcg subcutaneously or intravenously 1, 3
• Provide hypotonic fluid replacement for existing deficit 1

Nephrogenic diabetes insipidus:

• Discontinue causative medications (lithium, amphotericin) if possible 3
• Correct underlying electrolyte abnormalities (hypokalemia, hypercalcemia) 3
• Consider thiazide diuretics or amiloride for chronic management 3

Hypovolemic hypernatremia from extrarenal losses:

• Replace volume with hypotonic fluids (D5W or 0.45% saline) 6, 3
• Address the source of fluid loss (diarrhea, burns, excessive sweating) 3

Critical Safety Considerations

• Avoid rapid correction in chronic hypernatremia: Correction faster than 12 mmol/L per day risks cerebral edema, though definitive evidence of harm is limited 4
• Monitor closely when initiating renal replacement therapy: Patients with chronic hypernatremia can experience rapid sodium drops during dialysis 1
• Reassess frequently: Check serum sodium every 2-4 hours initially, then adjust monitoring frequency based on response 2, 4
• Adjust for glucose: Correct measured sodium for hyperglycemia (add 1.6 mEq/L for each 100 mg/dL glucose >100 mg/dL) 5

Common Pitfalls to Avoid

• Undercorrection is more dangerous than overcorrection: Delayed correction of hypernatremia is associated with increased hospital stay and mortality 4
• Failing to account for ongoing losses: Calculate and replace insensible losses (500-1000 mL/day) plus any measured losses 2
• Using isotonic fluids in hypernatremia: This will not correct the free water deficit and may worsen the condition 6, 3
• Missing diabetes insipidus: If urine remains dilute despite hypernatremia, investigate for central or nephrogenic diabetes insipidus 3, 2