What is the management of hypernatremia?

Management of Hypernatremia

For hypernatremia, restore plasma tonicity by administering hypotonic fluids (0.45% NaCl or D5W) with a correction rate not exceeding 0.4 mmol/L per hour for chronic cases, while acute hypernatremia can be corrected more rapidly to prevent cellular dehydration. 1

Initial Assessment and Classification

• Hypernatremia is defined as plasma sodium concentration >145 mmol/L and should be classified by duration (acute vs. chronic), severity (mild, moderate, threatening), and volume status (hypervolemic, hypovolemic, euvolemic) 1

• Determine the rapidity of onset: if hypernatremia developed acutely (over hours), rapid correction improves prognosis; if it developed slowly (over days), slow correction is mandatory 1

• Assess volume status through clinical examination: look for signs of hypovolemia (orthostatic hypotension, dry mucous membranes, decreased skin turgor) versus hypervolemia (edema, jugular venous distention) 2

Treatment Based on Pathogenesis

Hypervolemic Hypernatremia

• Acute hypervolemic hypernatremia is typically secondary to increased sodium intake from hypertonic NaCl or NaHCO3 solutions 1

• Chronic hypervolemic hypernatremia may indicate primary hyperaldosteronism 1

• Treatment involves diuretics to promote renal sodium excretion combined with free water administration 3

Euvolemic Hypernatremia (Diabetes Insipidus)

• Neurogenic (central) diabetes insipidus may be triggered by traumatic, vascular, or infectious events affecting the hypothalamus or pituitary 1

• Nephrogenic diabetes insipidus can result from medications (particularly lithium) or metabolic disturbances like hypokalemia 1

• Patients with renal concentrating defects require hypotonic fluid replacement to prevent worsening hypernatremia, as isotonic fluids will exacerbate the condition 2

Hypovolemic Hypernatremia

• Results from renal losses (osmotic diuresis, diuretics) or extrarenal losses (diarrhea, burns, excessive sweating) 1

• Treatment focuses on volume repletion with hypotonic fluids 1

Fluid Selection and Administration

• Primary hypotonic fluid options include:

  • 0.45% NaCl (half-normal saline): contains 77 mEq/L sodium, appropriate for moderate hypernatremia 2
  • 0.18% NaCl (quarter-normal saline): contains 31 mEq/L sodium, provides greater free water content for more aggressive correction 2
  • D5W (5% dextrose in water): provides pure free water replacement 2

• Avoid isotonic fluids (0.9% NaCl) in patients with renal concentrating defects, as this will worsen hypernatremia 2

Correction Rate Guidelines

Chronic Hypernatremia (Developed Over Days)

• Maximum correction rate: 0.4 mmol/L per hour to prevent cerebral edema 1

• Alternative guideline: reduce sodium at 10-15 mmol/L per 24 hours 2

• Correction rates faster than 48-72 hours for severe hypernatremia have been associated with increased risk of pontine myelinolysis 2

Acute Hypernatremia (Developed Over Hours)

• Rapid correction is safe and improves prognosis by preventing effects of cellular dehydration 1

• A study of critically ill patients found no evidence that rapid correction (>0.5 mmol/L per hour or >12 mmol/L per 24 hours) was associated with higher mortality, seizures, altered consciousness, or cerebral edema 4

• Manual chart review of 278 patients revealed not a single case of cerebral edema attributable to rapid hypernatremia correction 4

Special Populations

Critically Ill Patients

• Hypernatremia is common in intensive care units and is an independent risk factor for increased mortality 3

• Many critically ill patients have impaired consciousness and cannot regulate water balance through thirst, making physician-managed fluid balance critical 3

• The intensivist must carefully provide adequate sodium and water balance, as these patients cannot self-regulate 3

Pediatric Patients

• Hypernatremia in children most frequently results from excessive water loss with diarrhea and excessive solute load from inappropriate formula preparation 5

• The rate of rehydration is most vital: if accomplished too rapidly, children develop edema, increased intracranial pressure, stupor, and convulsions 5

• Rehydration should be accomplished slowly over 24-72 hours depending on severity 5

• Monitor regularly with electrolytes, careful weight determination, and intake/output records 5

• Approximately 10-15% of children with serum sodium ≥160 mEq/L will have permanent neurological deficits 5

Monitoring During Treatment

• Check serum sodium levels frequently during correction to ensure adherence to target correction rates 1, 3

• Track daily weights and fluid balance meticulously 2

• Monitor for signs of cerebral edema: altered mental status, seizures, headache 4

• For severe hypernatremia, consider ICU-level monitoring 3

Common Pitfalls to Avoid

• Overly rapid correction of chronic hypernatremia can cause cerebral edema, seizures, and permanent neurological damage 1, 5

• Using isotonic saline in patients with diabetes insipidus or renal concentrating defects will worsen hypernatremia 2

• Inadequate monitoring during correction can lead to overcorrection or undercorrection 3

• Failing to address the underlying cause (medication review, treatment of diabetes insipidus, correction of volume status) 1, 3