What are the causes and treatment of hypernatremia?

Causes and Treatment of Hypernatremia

Hypernatremia (serum sodium >145 mmol/L) is primarily caused by water deficit relative to sodium content and requires careful correction at a rate of 10-15 mmol/L/24h to prevent neurological complications.

Causes of Hypernatremia

Based on Volume Status

1. Hypovolemic Hypernatremia

   • Excessive water loss exceeding sodium loss:
     • Gastrointestinal losses (diarrhea, vomiting)
     • Excessive sweating
     • Burns
     • Osmotic diuresis (hyperglycemia, mannitol)
     • Renal losses (diuretic use, post-obstructive diuresis)

2. Euvolemic Hypernatremia

   • Pure water deficit:
     • Inadequate water intake (impaired thirst mechanism)
     • Insensible losses (fever, tachypnea)
     • Diabetes insipidus (central or nephrogenic)

3. Hypervolemic Hypernatremia

   • Excessive sodium gain:
     • Iatrogenic (hypertonic saline, sodium bicarbonate administration)
     • Excessive sodium intake
     • Primary hyperaldosteronism
     • Cushing's syndrome

Special Considerations

• In neonates and very low birth weight infants (VLBWI), hypernatremia often results from incorrect replacement of transepidermal water loss, inadequate water intake, or excessive sodium intake 1
• In critically ill patients, hypernatremia is often iatrogenic due to inadequate free water prescription 2
• In patients with cirrhosis, hypernatremia is less common than hyponatremia but can occur with excessive diuresis 1

Diagnostic Approach

1. Confirm true hypernatremia - exclude pseudohypernatremia 3
2. Assess volume status - physical examination for signs of dehydration or fluid overload
3. Measure urine sodium and osmolality - helps determine the cause
4. Calculate free water deficit using the formula:
   • Free water deficit = 0.6 × body weight (kg) × [(measured Na⁺/140) - 1]

Treatment of Hypernatremia

General Principles

1. Identify and treat the underlying cause 4, 3

2. Determine chronicity:

   • Acute hypernatremia (<48 hours): Can correct more rapidly
   • Chronic hypernatremia (>48 hours): Slower correction required 5

3. Calculate water deficit and replace appropriately

4. Rate of correction:

   • For chronic hypernatremia: Reduce sodium by 10-15 mmol/L/24h 1
   • For acute hypernatremia: Can correct more rapidly but still with caution

Specific Treatment Based on Volume Status

1. Hypovolemic Hypernatremia:

   • Initial volume resuscitation with isotonic fluids (0.9% saline)
   • Once hemodynamically stable, switch to hypotonic fluids (0.45% saline or 5% dextrose)

2. Euvolemic Hypernatremia:

   • Hypotonic fluid administration (0.45% saline or 5% dextrose in water)
   • For diabetes insipidus: Treat with desmopressin (DDAVP) if central type 5

3. Hypervolemic Hypernatremia:

   • Diuretics to promote sodium excretion
   • Hypotonic fluids
   • Consider hemodialysis in severe cases with volume overload

Special Populations

• Neonates and VLBWI: Assess intravascular volume and hydration status. In case of symptomatic hypovolemia, replace plasma volume. Avoid rapid correction 1

• Critically ill patients: Careful monitoring of fluid balance and frequent electrolyte checks 2

• Patients with cirrhosis: Cautious use of diuretics; monitor for worsening ascites 1

Monitoring During Treatment

• Frequent serum sodium measurements (every 2-4 hours initially)
• Monitor neurological status for signs of cerebral edema
• Track fluid balance
• Assess for signs of volume overload or dehydration

Complications of Treatment

• Too rapid correction: Cerebral edema, seizures, and neurological injury 1
• Inadequate correction: Persistent neurological symptoms, increased mortality

Pitfalls to Avoid

1. Failure to identify the underlying cause
2. Overly rapid correction in chronic hypernatremia
3. Inadequate monitoring during treatment
4. Focusing only on sodium correction without addressing volume status
5. Iatrogenic causes - particularly in hospitalized patients receiving IV fluids

Remember that hypernatremia, especially when severe or symptomatic, is associated with high morbidity and mortality. Proper identification of the cause and careful correction of the sodium level are essential for improving outcomes.