Clinical Signs Of Hypernatremia
Typically only with acute increase in Na+ >170 mEq/L1
Largely neurologic manifestations
Mentation changes
Seizures
Chronic changes subclinical
Idiogenic osmoles in neurons offset the change in osmolality.
Author Insight
Hypernatremia is not possible in patients with access to water and an intact thirst mechanism.
Considerations For Treatment
Treatment is predominantly impacted by underlying cause, acuity versus chronicity, volume status, and need for fluid resuscitation.
Address underlying cause when possible.
Gradually reduce Na+ to avoid osmotic injury unless change is known to be acute.
Maximum rate of change: 0.5-1 mEq/hour
Use of a hypotonic fluid is most often required.
Serial Na+ monitoring is required every 4 to 8 hours initially, then every 12 to 24 hours once desired change in Na+ is achieved.
Case Example of Pure Water Loss
20-kg patient with Na+ = 160 mEq/L (normal Na+ assumed to be 145 mEq/L)
Free water deficit: 0.6 × BW × (Na+patient/Na+normal − 1)
0.6 × 20 kg (160/145 − 1) = 1.24 L or 1,240 mL
Safe replacement: desired Na+ change/0.5-1 mEq/hour
(160 − 145)/0.5-1= 15 to 30 hours
Rate of D5W with correction over 30 hours
1,240 mL/30 hours = 41 mL/hour
Rate of 0.45% NaCl with correction over 30 hours
(1,240 mL/30 hours) × 2 = 82 mL/hour
Case Example of Hypotonic Loss
In a 10-kg hypotensive patient with Na+ = 160 mEq/L, an initial fluid resuscitation bolus of 15 mL/kg isotonic BES (Na+ = 140 mEq/L) should be planned for administration over 30 minutes.
Change in Na+ = (Na+patient − Na+fluid)/(0.6 × BW + 1)
(160 − 140)/(0.6 × 10 + 1) = 2.8 mEq per liter of fluid administered
The patient will receive 0.15 L (15 mL/kg × 10 kg) over 30 minutes. Expected Na+ change is 2.8 mEq/L × 0.15 L = 0.42 mEq/30 minutes or 0.84 mEq/hour; <0.5-1 mEq/hour is considered a safe amount.
BES = balanced electrolyte solution, BW = body weight (in kg), D5W = dextrose 5% in water, Na+ = sodium, NaCl = sodium chloride
Editor's Note: An earlier version of this article contained an illustrative algorithm.