What are the causes and management of hypernatremia?

Hypernatremia: Causes and Management

Hypernatremia, defined as serum sodium >145 mmol/L, is often iatrogenic and requires careful management with correction rates tailored to the duration of the condition to prevent neurological complications.

Causes of Hypernatremia

Hypernatremia occurs when plasma sodium concentration exceeds 145 mmol/L and can be classified based on volume status and etiology:

Based on Volume Status

• Hypovolemic hypernatremia: Results from water loss exceeding sodium loss 1, 2

  • Renal losses: Osmotic diuresis, diuretic use, post-obstructive diuresis 2
  • Extrarenal losses: Gastrointestinal (diarrhea, vomiting), skin (excessive sweating, burns), respiratory losses 2, 3

• Euvolemic hypernatremia: Primarily seen in diabetes insipidus 1, 2

  • Central/neurogenic diabetes insipidus: Due to traumatic, vascular, or infectious events affecting ADH production 1
  • Nephrogenic diabetes insipidus: Due to renal resistance to ADH, often from medications (lithium), hypokalemia, or kidney disease 1, 2

• Hypervolemic hypernatremia: Excess sodium relative to water 1, 3

  • Acute: Excessive administration of hypertonic saline or sodium bicarbonate 1
  • Chronic: Primary hyperaldosteronism 1

Based on Duration

• Acute hypernatremia: Develops within 48 hours 4
• Chronic hypernatremia: Develops over more than 48 hours 4

Based on Severity

• Mild hypernatremia: Sodium slightly above 145 mmol/L 5
• Moderate hypernatremia: Intermediate elevation 1
• Severe hypernatremia: Significant elevation with neurological symptoms 1, 5

Common Causes in Critical Care Settings

• Impaired thirst or access to water (sedation, intubation, altered mental status) 3
• Excessive fluid losses (renal or non-renal) 3
• Iatrogenic causes (incorrect replacement of transepidermal water loss, inadequate water intake, or excessive sodium administration) 6

Clinical Manifestations

• Central nervous system dysfunction: Confusion, lethargy, irritability, seizures, coma 4, 5
• Pronounced thirst (in conscious patients) 4
• Neuromuscular symptoms: Weakness, spasticity, hyperreflexia 3
• Severe cases: Risk of hemorrhagic complications from vascular stretching and rupture 3

Diagnostic Approach

1. Exclude pseudohypernatremia 2
2. Confirm glucose-corrected sodium concentrations 2
3. Determine extracellular volume status (hypovolemic, euvolemic, or hypervolemic) 2
4. Measure urine sodium levels 2
5. Measure urine volume and osmolality 2
6. Check ongoing urinary electrolyte free water clearance 2
7. Determine arginine vasopressin/copeptin levels when appropriate 2
8. Assess other electrolyte disorders 2

Management of Hypernatremia

General Principles

• Primary goal: Restore plasma tonicity 1
• Correction rate depends on duration:
  • For acute hypernatremia (<48 hours): Faster correction is safer 1, 4
  • For chronic hypernatremia (>48 hours): Slow correction at no more than 0.4 mmol/L/hour or 8-10 mmol/L/day 1, 4

Treatment Steps

1. Identify and treat the underlying cause 2
2. Distinguish between acute and chronic hypernatremia 2
3. Calculate water deficit using appropriate formulas 2, 3
4. Select appropriate replacement solution 2
   • Hypotonic fluids (D5W, 0.45% saline) for most cases 5, 3
   • Consider hemodialysis for acute severe hypernatremia 4
5. Adjust treatment schedule based on clinical response 2
6. Consider specific therapy for diabetes insipidus if present 2
   • Desmopressin (Minirin) for central diabetes insipidus 4

Special Considerations

• Rapid correction of chronic hypernatremia can lead to cerebral edema, seizures, and neurological injury 6
• Recommended reduction rate: 10-15 mmol/L/24h for chronic hypernatremia 6
• Close monitoring is essential during correction 4, 3
• Hemodialysis may be considered for acute hypernatremia (<24 hours) 4
• Caution with renal replacement therapy in chronic hypernatremia to avoid rapid drops in sodium 4

Monitoring During Treatment

• Regular assessment of serum sodium levels 3
• Monitoring of clinical neurological status 3
• Adjustment of fluid therapy based on response 2, 3
• Vigilance for signs of cerebral edema if correction occurs too rapidly 4

Common Pitfalls to Avoid

• Overly rapid correction of chronic hypernatremia leading to cerebral edema 6, 4
• Inadequate monitoring during active correction 3
• Failure to identify and treat the underlying cause 2
• Inappropriate fluid selection for replacement 3
• Overlooking ongoing water losses during treatment 2, 3