Evaluation and Management of Hypernatremia
The initial step in the workup of hypernatremia should be to assess the patient's volume status and determine the underlying cause through measurement of urine osmolality and sodium concentration. 1, 2
Initial Assessment
- Confirm true hypernatremia by excluding pseudohypernatremia and checking glucose-corrected sodium concentrations 2
- Determine the extracellular volume status (hypovolemic, euvolemic, or hypervolemic) as this guides subsequent management 1, 2
- Measure urine sodium levels and osmolality to help identify the underlying cause 1, 2
- Assess urine volume and calculate urinary electrolyte free water clearance 2
- Check for other concurrent electrolyte disorders that may provide diagnostic clues 2
Diagnostic Algorithm Based on Volume Status
Hypovolemic Hypernatremia
- Characterized by water loss exceeding sodium loss 3
- Causes include gastrointestinal losses, excessive sweating, burns, and osmotic diuresis 4
- Urine osmolality is typically high (>700 mOsm/kg) and urine sodium is low (<20 mmol/L) unless renal sodium wasting is present 1, 2
Euvolemic Hypernatremia
- Characterized by pure water loss with normal total body sodium 3
- Common causes include diabetes insipidus, impaired thirst mechanism, or lack of access to water 4, 3
- Urine osmolality is typically low (<300 mOsm/kg) in diabetes insipidus 1, 2
Hypervolemic Hypernatremia
- Characterized by sodium gain exceeding water gain 3
- Causes include iatrogenic sodium administration, primary hyperaldosteronism, or Cushing's syndrome 2
- Urine sodium is typically high (>100 mmol/L) 1, 2
Management Principles
- Distinguish between acute (<48 hours) and chronic (>48 hours) hypernatremia, as this determines the rate of correction 3, 2
- For chronic hypernatremia, correction should not exceed 8-10 mmol/L/day to prevent neurological complications 3, 5
- For acute hypernatremia, more rapid correction may be considered, but close monitoring is essential 3
Treatment Approach
Step 1: Calculate Water Deficit
- Water deficit (L) = Current total body water × [(Current Na⁺/140) - 1] 2
- Current total body water ≈ 0.5-0.6 × body weight (kg) 2
Step 2: Select Appropriate Fluid
- For hypovolemic hypernatremia: Begin with isotonic saline to restore intravascular volume, then switch to hypotonic fluids 1, 2
- For euvolemic hypernatremia: Use hypotonic fluids (0.45% saline or 5% dextrose in water) 3, 2
- For hypervolemic hypernatremia: Consider diuretics along with hypotonic fluids 2
Step 3: Determine Rate of Correction
- For chronic hypernatremia (>48 hours): Aim for correction of 8-10 mmol/L/day 3, 5
- For acute hypernatremia (<48 hours): More rapid correction may be considered, but still requires close monitoring 3
Step 4: Monitor Response
- Check serum sodium every 2-4 hours initially, then every 4-6 hours as stabilization occurs 2
- Adjust fluid therapy based on serum sodium trends 2
- Monitor for signs of cerebral edema during correction 5
Special Considerations
- For diabetes insipidus, consider desmopressin (DDAVP) administration 3
- In cases of severe hypernatremia with neurological symptoms, hemodialysis may be an effective option for rapid normalization of serum sodium levels 3
- Patients with impaired thirst mechanisms require close monitoring and scheduled fluid intake 4
Common Pitfalls to Avoid
- Overly rapid correction of chronic hypernatremia, which can lead to cerebral edema 3, 5
- Inadequate monitoring during active correction 1
- Failure to identify and treat the underlying cause 1, 2
- Inappropriate fluid selection based on volume status 2
By systematically assessing volume status and measuring urine parameters, clinicians can determine the underlying cause of hypernatremia and implement appropriate fluid replacement strategies while avoiding dangerous rapid corrections.