What is the appropriate management of hypernatremia?

Management of Hypernatremia

For hypernatremia, the cornerstone of treatment is administering hypotonic fluids (0.45% NaCl, 0.18% NaCl, or D5W) to replace free water deficit, with a maximum correction rate of 10-15 mmol/L per 24 hours for chronic cases to prevent cerebral edema. 1

Initial Assessment and Diagnostic Approach

Determine the chronicity of hypernatremia (acute <48 hours vs. chronic >48 hours), as this fundamentally dictates your correction rate 1, 2. Acute hypernatremia can be corrected more rapidly—up to 1 mmol/L/hour if severely symptomatic—while chronic hypernatremia requires slower correction at 10-15 mmol/L per 24 hours 1, 2.

Assess volume status through physical examination to classify hypernatremia as hypovolemic, euvolemic, or hypervolemic 1, 3:

• Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, tachycardia 1
• Euvolemic: normal vital signs, no edema, no signs of dehydration 3
• Hypervolemic: peripheral edema, jugular venous distention, pulmonary congestion 1

Measure urine osmolality and urine sodium to determine the underlying mechanism 3:

• Urine osmolality <300 mOsm/kg suggests diabetes insipidus (central or nephrogenic) 3
• Urine osmolality >600 mOsm/kg indicates appropriate renal response to hypertonicity 3
• Urine sodium <20 mEq/L suggests extrarenal losses (GI losses, burns, sweating) 3
• Urine sodium >20 mEq/L suggests renal losses or osmotic diuresis 3

Fluid Selection and Administration

Use hypotonic fluids as first-line therapy for hypernatremia correction 1:

• 0.45% NaCl (half-normal saline): contains 77 mEq/L sodium with osmolarity ~154 mOsm/L, appropriate for moderate hypernatremia 1
• 0.18% NaCl (quarter-normal saline): contains ~31 mEq/L sodium, providing more aggressive free water replacement for severe cases 1
• D5W (5% dextrose in water): delivers no renal osmotic load and is the preferred choice when pure free water replacement is needed, especially in nephrogenic diabetes insipidus 1

Never use isotonic saline (0.9% NaCl) as initial therapy because it delivers excessive osmotic load—requiring 3 liters of urine to excrete the osmotic load from just 1 liter of isotonic fluid—which will worsen hypernatremia, particularly in patients with renal concentrating defects 1.

Calculate the free water deficit using the formula: Desired increase in Na (mmol/L) × (0.5 × ideal body weight in kg) 1. This provides an estimate of total fluid requirements, though ongoing losses must be added.

Initial fluid administration rates 1:

• Adults: 25-30 mL/kg per 24 hours, then titrate based on serial sodium measurements
• Children: 100 mL/kg/24h for first 10 kg, 50 mL/kg/24h for next 10 kg, 20 mL/kg/24h for remaining weight

Correction Rate Guidelines and Safety

For chronic hypernatremia (>48 hours), limit correction to 10-15 mmol/L per 24 hours to prevent cerebral edema, seizures, and permanent neurological injury 1, 2. The brain adapts to chronic hypertonicity by synthesizing intracellular osmolytes over 48 hours; rapid correction causes water to rush into brain cells, leading to cerebral edema 1.

For acute hypernatremia (<48 hours), more rapid correction up to 1 mmol/L/hour is permissible if the patient is severely symptomatic, as the brain has not yet adapted 1, 2.

Check serum sodium every 2-4 hours initially during active correction, then every 6-12 hours once stable 1. Monitor daily weight, vital signs (supine and standing), fluid input/output, and urine specific gravity 1.

Treatment Based on Volume Status

Hypovolemic Hypernatremia

Administer hypotonic fluids to replace free water deficit at an initial rate of 4-14 mL/kg/h 1. This addresses both volume depletion and hypertonicity simultaneously.

For patients with severe burns or voluminous diarrhea, hypotonic fluids must match ongoing free water losses in addition to replacing the existing deficit 1. Total fluid volume often exceeds the calculated free water deficit because losses continue during treatment.

Euvolemic Hypernatremia (Diabetes Insipidus)

For nephrogenic diabetes insipidus, ongoing hypotonic fluid administration is required to match excessive free water losses 1. Isotonic fluids are absolutely contraindicated as they will worsen hypernatremia 1.

For central diabetes insipidus, consider desmopressin (DDAVP) in addition to hypotonic fluid replacement 4. However, desmopressin should not be used for nephrogenic DI as the kidneys cannot respond to ADH 1.

Implement a low-salt diet (<6 g/day) and protein restriction (<1 g/kg/day) for patients with euvolemic hypernatremia to reduce renal solute load 1.

Hypervolemic Hypernatremia

In cirrhotic patients with hypervolemic hypernatremia, discontinue intravenous fluid therapy and implement free water restriction 1. The goal is negative water balance rather than aggressive fluid administration 1.

For heart failure patients with hypernatremia, fluid restriction to 1.5-2 L/day is recommended after initial correction 1. Sodium restriction to <2 g daily is also advised 1.

Diuretics remain essential for volume management in heart failure patients but must be carefully balanced with hypernatremia correction 1. Diuresis should be slowed but maintained until fluid retention is eliminated, even if mild-to-moderate decreases in blood pressure or renal function occur 1.

Special Populations and Considerations

Older Adults

Older adults are at higher risk for both hypernatremia and complications from correction due to reduced renal function, cognitive impairment preventing recognition of thirst, and inability to access fluids 1. Use more conservative fluid rates and monitor closely for worsening azotemia 1.

Patients with Chronic Kidney Disease

Use more conservative fluid rates in CKD patients and closely monitor for worsening azotemia during correction 1. These patients have impaired ability to handle fluid loads.

Traumatic Brain Injury

Prolonged induced hypernatremia to control intracranial pressure is NOT recommended in traumatic brain injury patients 1. It requires an intact blood-brain barrier to be effective and may worsen cerebral contusions 1. There is a weak relationship between serum sodium and ICP, and risk of "rebound" ICP elevation exists during correction 1.

Monitoring Protocol

Daily monitoring should include 1:

• Serum sodium every 2-4 hours initially, then every 6-12 hours
• Daily weight measurement
• Supine and standing vital signs
• Fluid input and output with careful tracking
• Urine output, specific gravity/osmolarity, and urine electrolyte concentrations
• Serum electrolytes (potassium, chloride, bicarbonate)
• Renal function (BUN, creatinine) to evaluate for worsening azotemia
• Hematocrit and blood urea nitrogen to assess hydration status

Common Pitfalls to Avoid

Correcting chronic hypernatremia too rapidly (>10-15 mmol/L per 24 hours) can lead to cerebral edema, seizures, and permanent neurological injury 1, 2. This is the single most dangerous error in hypernatremia management.

Using isotonic saline as initial therapy will worsen hypernatremia, especially in patients with nephrogenic diabetes insipidus or renal concentrating defects 1. The only exception is brief use for immediate hemodynamic stabilization in true hypovolemic shock, followed by prompt switch to hypotonic fluids 1.

Inadequate monitoring during correction can result in overcorrection or undercorrection 1. Serum sodium must be checked frequently during active treatment.

Failing to identify and treat the underlying cause is a common pitfall 1. Hypernatremia is often iatrogenic, especially in vulnerable populations, and addressing the root cause is essential for preventing recurrence.

In heart failure patients, avoiding excessive fluid administration is critical 1. Combine IV hypotonic fluids with free water via nasogastric tube if needed, targeting 10-15 mmol/L correction per 24 hours 1.