Management of Hypernatremia in Adults
Administer hypotonic fluids—specifically 0.45% NaCl (half-normal saline), 0.18% NaCl (quarter-normal saline), or D5W (5% dextrose in water)—to replace the free water deficit, and never use isotonic saline (0.9% NaCl) as initial therapy because it delivers excessive osmotic load that worsens hypernatremia, especially in patients with impaired renal concentrating ability. 1
Initial Assessment and Diagnostic Workup
Assess the patient's clinical status by checking neurological symptoms (confusion, lethargy, seizures), vital signs (orthostatic hypotension, tachycardia), and volume status (skin turgor, mucous membrane moisture, jugular venous pressure). 1 Evaluate body weight and estimate body composition to determine fluid deficits. 1 Measure blood electrolyte concentrations, acid-base status, hematocrit, and blood urea nitrogen to assess hydration status. 1 Calculate fluid and electrolyte balance by tracking urine output, specific gravity, osmolarity, and urine electrolyte concentrations. 1
Check urine osmolality to determine renal concentrating ability: a value of 235 mOsm/kg is inappropriately low in hypernatremia, indicating either impaired renal concentrating ability or ongoing osmotic diuresis. 1 The presence of hypernatremia with inappropriately dilute urine and low urine sodium suggests extrarenal water loss or inadequate water intake with impaired renal concentrating ability. 1
Fluid Selection and Administration
Primary Hypotonic Fluid Options
Half-normal saline (0.45% NaCl) contains 77 mEq/L sodium with osmolarity ≈154 mOsm/L, making it appropriate for moderate hypernatremia correction. 1 This solution provides both free water and some sodium replacement. 1
Quarter-normal saline (0.18% NaCl) contains ≈31 mEq/L sodium, providing more aggressive free water replacement for severe cases. 1
D5W (5% dextrose in water) is the fluid of choice when pure free-water replacement is required because it adds no renal osmotic load; it is especially valuable in patients with nephrogenic diabetes insipidus or other renal concentrating defects. 1 D5W allows slow, controlled decrease in plasma osmolality. 1
Contraindicated Fluids
Isotonic saline (0.9% NaCl) must be avoided as initial therapy for hypernatremia; its high osmotic load would require ≈3 L of urine to excrete the load from just 1 L infused, risking further elevation of serum sodium, particularly in patients with impaired renal concentrating ability. 1 Isotonic saline may be used briefly only for immediate hemodynamic stabilization in true hypovolemic shock; it must be switched promptly to hypotonic fluids for ongoing hypernatremia management. 1
Correction Rate Guidelines
For chronic hypernatremia (duration >48 hours), the maximum safe correction is 10–15 mmol/L per 24 hours; faster correction can precipitate cerebral edema, seizures, and permanent neurologic injury. 1 A reduction rate of 10-15 mmol/L/24 hours is recommended to avoid complications. 1 The induced change in serum osmolality should not exceed 3 mOsm/kg H₂O per hour. 2
Correcting chronic hypernatremia faster than 10–15 mmol/L per 24 hours can cause cerebral edema, seizures, and potentially fatal brain herniation as brain cells rapidly gain water after loss of intracellular osmolytes. 1 Slower correction of chronic hypernatremia is critical because brain cells synthesize intracellular osmolytes over 48 hours to adapt to hyperosmolar conditions, and rapid correction can cause cerebral edema, seizures, and permanent neurological injury. 1
Acute hypernatremia can be corrected more rapidly, up to 1 mmol/L/hour if severely symptomatic. 1 Corrections faster than 48-72 hours have been associated with increased risk of pontine myelinolysis. 1
Initial Fluid Administration Rates
Adults: start hypotonic fluid at 25–30 mL/kg per 24 hours, then titrate according to clinical response and serial sodium measurements. 1 Fluid replacement should correct estimated deficits within the first 24 hours. 2
Children: use physiological maintenance rates—100 mL/kg/24 hours for the first 10 kg, 50 mL/kg/24 hours for the next 10 kg, and 20 mL/kg/24 hours for any additional weight. 1
Special Clinical Scenarios
Nephrogenic Diabetes Insipidus
Continuous hypotonic fluid replacement is required to match excessive free-water losses; isotonic fluids are absolutely contraindicated because they worsen hypernatremia. 1 Ongoing hypotonic fluid administration is required to match excessive free water losses, and desmopressin should not be used for nephrogenic DI. 1
Severe Burns or Voluminous Diarrhea
Hypotonic fluids must be administered to keep pace with ongoing free-water losses; total fluid volume often exceeds the calculated free-water deficit because losses continue during treatment. 1 Fluid composition should be matched to losses while providing adequate free water. 1
Patients with Renal or Cardiac Compromise
In patients with renal or cardiac compromise, monitoring of serum osmolality and frequent assessment of cardiac, renal, and mental status must be performed during fluid resuscitation to avoid iatrogenic fluid overload. 2
Monitoring During Treatment
Check serum sodium levels every 2-4 hours initially during active correction, then every 6-12 hours. 1 Monitor daily weight, supine and standing vital signs. 1 Track fluid input and output with careful tracking, as well as urine output, specific gravity/osmolarity, and urine electrolyte concentrations. 1 Assess renal function (BUN, creatinine) to evaluate for worsening azotemia. 1
Common Pitfalls to Avoid
Inadequate monitoring during correction can result in overcorrection or undercorrection. 1 Failing to identify and treat the underlying cause of hypernatremia, which is often iatrogenic, especially in vulnerable populations, is a common pitfall. 1 Using isotonic saline in patients with renal concentrating defects will exacerbate hypernatremia. 1