How to manage hypernatremia (elevated sodium levels)?

Management of Hypernatremia (Elevated Sodium)

For hypernatremia, restore plasma tonicity by replacing free water deficits with hypotonic fluids, correcting no faster than 0.4 mmol/L/hour (8-10 mmol/L per 24 hours) for chronic cases to prevent osmotic demyelination syndrome, while addressing the underlying cause. 1, 2

Initial Assessment and Diagnosis

Confirm true hypernatremia by excluding pseudohypernatremia and checking glucose-corrected sodium concentrations (add 1.6 mEq/L to sodium for each 100 mg/dL glucose >100 mg/dL). 3, 4

Determine the duration:

• Acute hypernatremia: <24-48 hours onset, can be corrected more rapidly 1, 2
• Chronic hypernatremia: >48 hours, requires slow correction to avoid cerebral edema 1, 2

Assess volume status through physical examination looking for:

• Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, tachycardia 3, 5
• Hypervolemic signs: edema, jugular venous distention 3
• Euvolemic appearance: normal volume status 1

Obtain urine studies:

• Urine osmolality and urine sodium concentration 4, 6
• Urine volume to assess ongoing losses 4
• Calculate urinary electrolyte-free water clearance 4

Differential Diagnosis by Volume Status

Hypervolemic hypernatremia (excess sodium):

• Acute: excessive hypertonic NaCl or NaHCO3 administration 1
• Chronic: primary hyperaldosteronism 1

Euvolemic hypernatremia (pure water deficit):

• Central diabetes insipidus: traumatic brain injury, neurosurgery, pituitary pathology, vascular events, infections 1, 6
• Nephrogenic diabetes insipidus: lithium therapy, hypokalemia, hypercalcemia 1, 6
• Consider measuring arginine vasopressin/copeptin levels to distinguish central from nephrogenic causes 4

Hypovolemic hypernatremia (water loss exceeds sodium loss):

• Renal losses: osmotic diuresis, loop diuretics 1, 4
• Extrarenal losses: gastrointestinal (diarrhea, vomiting), skin (burns, excessive sweating), respiratory 3, 1
• Impaired thirst mechanism or lack of water access in elderly or debilitated patients 5, 6

Treatment Algorithm

Step 1: Address Underlying Cause

• Stop offending medications (lithium, diuretics) 1
• Treat infections or CNS pathology 1
• Provide water access for patients with impaired thirst 5

Step 2: Calculate Water Deficit

Use the formula: Water deficit (L) = 0.5 × body weight (kg) × [(current Na/140) - 1] 4

Step 3: Determine Correction Rate

For acute hypernatremia (<24 hours):

• Rapid correction is safe and improves prognosis by preventing cellular dehydration 1
• Can correct at faster rates, even considering hemodialysis for severe cases 2

For chronic hypernatremia (>48 hours):

• Maximum correction rate: 0.4 mmol/L/hour or 8-10 mmol/L per 24 hours 1, 2
• Slower correction prevents osmotic demyelination syndrome and cerebral edema 1, 2

Step 4: Select Replacement Fluid

For mild-moderate hypernatremia or oral intake possible:

• Free water by mouth is preferred 5, 4

For severe hypernatremia or inability to take oral fluids:

• 0.45% NaCl (half-normal saline): 77 mEq/L sodium, osmolarity ~154 mOsm/L, appropriate for moderate hypernatremia 7
• 0.18% NaCl (quarter-normal saline): 31 mEq/L sodium, more hypotonic, for aggressive free water replacement 7
• D5W (5% dextrose in water): for severe hypernatremia or central pontine myelinolysis, provides pure free water 7

Avoid isotonic saline (0.9% NaCl) as it will worsen hypernatremia in patients unable to excrete free water appropriately. 7

Step 5: Calculate Infusion Rate

• Replace calculated water deficit over 48-72 hours for chronic hypernatremia 1, 2
• Add ongoing losses (insensible losses ~500-1000 mL/day plus measured urine output) 4
• Adjust infusion rate to achieve target correction of 8-10 mmol/L per 24 hours 1, 2

Step 6: Specific Treatment for Diabetes Insipidus

Central diabetes insipidus:

• Desmopressin (DDAVP): primary treatment to replace ADH 1, 2
• Continue hypotonic fluid replacement as needed 1

Nephrogenic diabetes insipidus:

• Correct underlying causes (stop lithium, correct hypokalemia/hypercalcemia) 1
• Thiazide diuretics may paradoxically reduce urine output 6
• Hypotonic fluid replacement to match ongoing losses 1, 4

Monitoring During Treatment

Check serum sodium every 2-4 hours initially during active correction, then every 6-8 hours once stable. 2, 4

Monitor for signs of overcorrection:

• Neurological changes suggesting osmotic demyelination (dysarthria, dysphagia, quadriparesis) 3
• If correction is too rapid, slow or temporarily stop hypotonic fluids 2

Track daily weights and fluid balance to assess adequacy of replacement. 4

Reassess urine osmolality and electrolytes to monitor response and adjust therapy. 4

Common Pitfalls to Avoid

Never correct chronic hypernatremia faster than 8-10 mmol/L per 24 hours as this risks cerebral edema and osmotic demyelination syndrome. 1, 2

Do not use isotonic saline in patients with renal concentrating defects (nephrogenic diabetes insipidus) as this will exacerbate hypernatremia. 7

Avoid rapid sodium drops when initiating renal replacement therapy in patients with chronic hypernatremia—use appropriate dialysate sodium concentrations. 2

In patients with central pontine myelinolysis, reduce sodium at 10-15 mmol/L per 24 hours using D5W as primary fluid. 7

For patients with voluminous diarrhea or severe burns, match fluid composition to losses while providing adequate free water. 7