What are the primary goals and treatment strategies for managing hypernatremia?

Hypernatremia Management

Primary Treatment Goals and Correction Principles

The primary goal is to restore plasma tonicity through controlled water replacement, with correction rates strictly determined by the duration of hypernatremia to prevent cerebral edema. 1

Acute vs. Chronic Hypernatremia

• Acute hypernatremia (onset <24-48 hours) can be corrected rapidly without significant risk of neurological complications, as the brain has not yet adapted through osmolyte accumulation 1, 2
• Chronic hypernatremia (onset >48 hours) requires slow correction at no more than 10-15 mmol/L per 24 hours (maximum 0.4 mmol/L/hour) to avoid cerebral edema, seizures, and permanent neurological injury 1, 2, 3

Diagnostic Classification and Treatment Algorithm

Step 1: Determine Volume Status

Hypernatremia must be classified as hypervolemic, euvolemic, or hypovolemic, as this determines the treatment approach. 2, 3

Hypervolemic Hypernatremia

• Acute form: typically iatrogenic from hypertonic NaCl or NaHCO₃ infusions 2
• Chronic form: may indicate primary hyperaldosteronism 2
• Treatment: hypotonic infusions in conjunction with diuretics to achieve negative sodium balance 4, 5
• Critical point: patients with 20L fluid accumulation need negative cation balance, not more water 4

Euvolemic Hypernatremia (Diabetes Insipidus)

• Central (neurogenic) DI: caused by traumatic, vascular, or infectious CNS events 2
• Nephrogenic DI: pharmacological (lithium) or metabolic (hypokalemia) causes 2
• Treatment: free water replacement plus specific therapy for DI (desmopressin for central, thiazides for nephrogenic) 3

Hypovolemic Hypernatremia

• Causes: renal losses (osmotic diuresis, diuretics) or extrarenal losses (GI, skin, respiratory) 2, 3
• Treatment: initial volume resuscitation with isotonic saline, then transition to hypotonic fluids once hemodynamically stable 6, 3

Step 2: Assess Severity and Symptoms

• Mild: 146-149 mmol/L
• Moderate: 150-159 mmol/L
• Severe/Threatening: ≥160 mmol/L 2

Symptomatic patients (altered mental status, seizures, focal neurological deficits) require urgent but controlled correction regardless of severity. 6

Fluid Replacement Strategy

Calculating Water Deficit

Water deficit (L) = 0.6 × body weight (kg) × [(current Na/140) - 1] 3

Selecting Replacement Fluids

• Hypotonic solutions (D5W, 0.45% NaCl, or 0.18% NaCl) are required for hypernatremia correction 6, 3
• D5W (5% dextrose) is preferred as it delivers no renal osmotic load and allows controlled plasma osmolality reduction 7
• 0.45% NaCl provides both free water and some sodium replacement for moderate hypernatremia 7
• Avoid isotonic saline in established hypernatremia as it delivers excessive osmotic load (requires 3L urine to excrete osmotic load from 1L infused) 7

Administration Rates

For chronic hypernatremia, reduce sodium by maximum 10-15 mmol/L per 24 hours (0.4 mmol/L/hour). 1, 2, 3

• Initial fluid rate: 25-30 mL/kg/24h in adults 7
• Pediatric rates: 100 mL/kg/24h for first 10kg, 50 mL/kg/24h for 10-20kg, 20 mL/kg/24h for remaining weight 7

Critical Monitoring Requirements

• Check serum sodium every 2-4 hours during active correction 3
• Monitor for signs of cerebral edema: headache, altered mental status, seizures 1, 2
• Daily weights and strict fluid balance tracking 1
• Assess ongoing losses (urine output, GI losses, insensible losses) and replace accordingly 3

Special Populations

Neonates and Very Low Birth Weight Infants

• Therapeutic measures based on etiology assessment 1
• Symptomatic hypovolemia requires volume replacement first 1
• Slow correction rate of 10-15 mmol/L/24h with daily weight and electrolyte monitoring 1

ICU Patients with Fluid Overload

• Do not give more water to patients with massive fluid accumulation (e.g., 20L positive balance) 4
• Focus on negative cation balance through diuretics plus hypotonic solutions 4, 5
• Hypervolemic hypernatremia in ICU is often iatrogenic from hypertonic infusions 5

Patients with Nephrogenic Diabetes Insipidus

• Require ongoing hypotonic fluid administration to match excessive free water losses 7
• Isotonic fluids will worsen hypernatremia in these patients 7

Common Pitfalls to Avoid

• Too rapid correction of chronic hypernatremia induces cerebral edema, seizures, and permanent neurological injury 1, 2, 3
• Failing to identify and treat underlying cause (DI, osmotic diuresis, excessive losses) 1, 3
• Using isotonic saline for established hypernatremia correction 7, 6
• Inadequate monitoring leading to undercorrection or overcorrection, both associated with poor prognosis 1
• Infusing hypertonic solutions in ICU patients without clear indication 5
• Treating hypervolemic hypernatremia with more water instead of negative sodium balance 4

Additional Therapy Considerations

• Central DI: desmopressin (DDAVP) to replace ADH 3
• Nephrogenic DI: thiazide diuretics, amiloride (for lithium-induced), NSAIDs 3
• Correct concurrent electrolyte disorders (hypokalemia worsens nephrogenic DI) 2, 3
• Address impaired thirst mechanism or lack of water access in elderly/disabled patients 6

The correction rate should never exceed 12 mmol/L per 24 hours to prevent rebounding brain edema, even in severe cases. 4