How do you treat hypernatremia in patients, particularly the elderly and those with underlying medical conditions?

Treatment of Hypernatremia

Treat hypernatremia by 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 hypernatremia (>48 hours) to prevent cerebral edema and neurological injury. 1

Initial Assessment and Volume Status Determination

Determine the patient's volume status and chronicity of hypernatremia before initiating treatment 1:

• Hypovolemic hypernatremia: Signs include orthostatic hypotension, dry mucous membranes, decreased skin turgor, tachycardia, and low urine output 1
• Euvolemic hypernatremia: Normal volume status with impaired water intake or diabetes insipidus 1
• Hypervolemic hypernatremia: Presence of edema, ascites, or jugular venous distention 1

Assess chronicity by determining if hypernatremia developed over <48 hours (acute) or >48 hours (chronic), as this dictates correction rates 1, 2

Measure urine osmolality and sodium to identify the underlying mechanism 1, 3:

• Urine osmolality <235 mOsm/kg with hypernatremia indicates impaired renal concentrating ability or diabetes insipidus 1
• Urine sodium helps distinguish renal from extrarenal losses 3

Fluid Selection and Administration

Never use isotonic saline (0.9% NaCl) as initial therapy for hypernatremia, especially in patients with nephrogenic diabetes insipidus or renal concentrating defects, as this will worsen hypernatremia 1

Hypotonic Fluid Options

Select from the following hypotonic solutions based on severity 1:

• 0.45% NaCl (half-normal saline): Contains 77 mEq/L sodium with osmolarity ~154 mOsm/L, appropriate for moderate hypernatremia correction 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 allows slow, controlled decrease in plasma osmolality; preferred for hypernatremic dehydration 4

Initial Fluid Administration Rates

For hypovolemic hypernatremia, begin with an initial rate of 4-14 mL/kg/h 1

For adults without severe volume depletion, use maintenance rates of 25-30 mL/kg/24 hours 4

Correction Rate Guidelines

Chronic Hypernatremia (>48 hours)

The maximum correction rate is 10-15 mmol/L per 24 hours to prevent cerebral edema, seizures, and permanent neurological injury 1

Slower correction is critical because brain cells synthesize intracellular osmolytes over 48 hours to adapt to hyperosmolar conditions; rapid correction causes cerebral edema 1

Monitor serum sodium every 2-4 hours initially during active correction, then every 6-12 hours 1

Acute Hypernatremia (<48 hours)

Acute hypernatremia can be corrected more rapidly, up to 1 mmol/L/hour if severely symptomatic 1

However, even in acute cases, avoid exceeding 10-15 mmol/L per 24 hours unless life-threatening symptoms are present 1

Special Populations and Clinical Scenarios

Elderly Patients

Older adults are at higher risk for both hypernatremia and complications from correction due to reduced renal function affecting sodium and water handling 1

Cognitive impairment may prevent recognition of thirst or ability to access fluids 1

Use conservative correction rates (10 mmol/L per 24 hours) in elderly patients with multiple comorbidities 1

Patients with Underlying Medical Conditions

Heart failure patients: Combine IV hypotonic fluids with free water via nasogastric tube if needed, targeting 10-15 mmol/L correction per 24 hours 1

After initial correction, implement fluid restriction (1.5-2 L/day) with careful monitoring of serum sodium and fluid balance 1

Cirrhosis patients: For hypervolemic hypernatremia, focus on attaining negative water balance rather than aggressive fluid administration 1

Discontinue intravenous fluid therapy and implement free water restriction 1

Nephrogenic diabetes insipidus: Requires ongoing hypotonic fluid administration to match excessive free water losses 1

Avoid isotonic saline entirely, as this exacerbates hypernatremia in patients with renal concentrating defects 1

Severe Burns or Voluminous Diarrhea

Match fluid composition to ongoing losses while providing adequate free water 1

Hypotonic fluids are required to keep up with ongoing free water losses 1

Monitoring Protocol

Track the following parameters during treatment 1:

• Serum sodium levels: Every 2-4 hours initially, then every 6-12 hours
• Daily weight: Monitor for appropriate fluid balance
• Vital signs: Supine and standing blood pressure, heart rate
• Fluid input and output: Careful tracking with urine output, specific gravity/osmolarity
• Neurological status: Watch for confusion, seizures, or altered mental status

Calculate free water deficit using the formula: Desired increase in Na (mmol/L) × (0.5 × ideal body weight in kg) 1

Common Pitfalls to Avoid

Correcting chronic hypernatremia too rapidly leads to cerebral edema, seizures, and neurological injury 1

Corrections faster than 48-72 hours have been associated with increased risk of pontine myelinolysis 1

Using isotonic saline in patients with renal concentrating defects will worsen hypernatremia 1

Inadequate monitoring during correction can result in overcorrection or undercorrection 1

Failing to identify and treat the underlying cause, which is often iatrogenic, especially in vulnerable populations 1

Additional Considerations for Specific Etiologies

For patients with diabetes insipidus, consider desmopressin (for central DI) in addition to free water replacement 2

Desmopressin should not be used for nephrogenic diabetes insipidus 1

Address inadequate water intake by ensuring access to free water and assisting patients who cannot drink independently 4

Replace ongoing losses from diarrhea, vomiting, or excessive sweating with appropriate hypotonic fluids 4