How is hypernatremia classified?

Hypernatremia Classification

Hypernatremia is classified based on serum sodium level (>145 mmol/L) and further categorized by volume status (hypovolemic, euvolemic, or hypervolemic) and severity (mild, moderate, or severe). 1, 2

Classification by Severity

• Mild hypernatremia: Serum sodium 146-150 mmol/L 2
• Moderate hypernatremia: Serum sodium 151-159 mmol/L 2
• Severe/threatening hypernatremia: Serum sodium ≥160 mmol/L 2

Classification by Volume Status

1. Hypovolemic Hypernatremia

• Characterized by decreased extracellular fluid volume with water loss exceeding sodium loss 2
• Common causes include:
  • Renal losses (osmotic diuresis, diuretic use) 2
  • Extrarenal losses (excessive sweating, diarrhea, burns) 2, 3
• Clinical signs include dry mucous membranes, decreased skin turgor, orthostatic hypotension 3

2. Euvolemic Hypernatremia

• Characterized by normal extracellular fluid volume with pure water deficit 2
• Common causes include:
  • Diabetes insipidus (central or nephrogenic) 2, 3
  • Inadequate water intake (impaired thirst mechanism, lack of access to water) 4, 3
• Clinical signs include thirst (if thirst mechanism intact) without signs of volume depletion 3

3. Hypervolemic Hypernatremia

• Characterized by increased extracellular fluid volume with sodium gain exceeding water gain 2
• Common causes include:
  • Iatrogenic administration of hypertonic saline or sodium bicarbonate 2, 3
  • Primary hyperaldosteronism (chronic form) 2
• Clinical signs include edema, hypertension 2

Classification by Duration

• Acute hypernatremia: Develops within 48 hours 2, 3
• Chronic hypernatremia: Develops over more than 48 hours 2, 3

Clinical Implications of Classification

• The classification guides treatment approach and correction rate 2, 3
• Acute hypernatremia can be corrected more rapidly (within 24 hours) 3
• Chronic hypernatremia requires slower correction (no more than 8-10 mmol/L/day) to prevent cerebral edema 2, 3
• Severe hypernatremia with neurological symptoms may require more aggressive intervention 3

Diagnostic Approach Based on Classification

• Assess volume status through clinical examination and laboratory values 3
• Measure urine osmolality and sodium to differentiate between causes 1
• For euvolemic hypernatremia, evaluate for diabetes insipidus by checking urine specific gravity and response to desmopressin 2, 3
• For hypervolemic hypernatremia, evaluate for excessive sodium intake or primary hyperaldosteronism 2

Treatment Considerations Based on Classification

• Hypovolemic hypernatremia: Replace volume with isotonic fluids initially, followed by hypotonic fluids 3
• Euvolemic hypernatremia: Provide free water replacement and treat underlying cause (e.g., desmopressin for central diabetes insipidus) 2, 3
• Hypervolemic hypernatremia: Remove excess sodium through diuresis or dialysis 2, 3
• Correction rate should not exceed 10-15 mmol/L/24h for chronic hypernatremia to prevent neurological complications 1, 2

Common Pitfalls in Management

• Overly rapid correction of chronic hypernatremia can lead to cerebral edema, seizures, and neurological injury 1
• Inadequate monitoring during correction can lead to complications 3
• Failure to identify and treat the underlying cause can result in recurrence 2, 3