What are the causes and treatment options for hypernatremia?

Causes and Treatment of Hypernatremia

Causes of Hypernatremia

Hypernatremia (serum sodium >145 mmol/L) reflects an imbalance in water balance, most commonly from excessive free water loss rather than sodium excess. 1, 2

Classification by Volume Status

Hypovolemic Hypernatremia (most common):

• Renal losses: osmotic diuresis, loop diuretics 2
• Extrarenal losses: diarrhea, vomiting, burns, excessive sweating 2, 3
• Inadequate water intake with impaired thirst mechanism or lack of access to water 3

Euvolemic Hypernatremia:

• Diabetes insipidus is the primary cause 2
  • Central (neurogenic): traumatic brain injury, neurosurgery, vascular events, infections 2
  • Nephrogenic: lithium therapy, hypokalemia, hypercalcemia, chronic kidney disease 2

Hypervolemic Hypernatremia (least common):

• Acute: excessive hypertonic saline or sodium bicarbonate administration 2
• Chronic: primary hyperaldosteronism 2

Special Populations

• Critically ill patients: impaired consciousness prevents thirst-driven water intake, making them dependent on physician-managed fluid balance 4
• Pediatric patients: hypernatremic dehydration carries the highest morbidity and mortality compared to other dehydration types, primarily from CNS dysfunction 5

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Treatment of Hypernatremia

Critical Correction Rate Guidelines

The single most important principle: chronic hypernatremia (>48 hours) must not be corrected faster than 10 mmol/L per 24 hours (maximum 0.4 mmol/L/hour) to prevent cerebral edema, seizures, and permanent neurological injury. 6, 1, 2

• Acute hypernatremia (<24-48 hours): can be corrected more rapidly, up to 1 mmol/L/hour if severely symptomatic 6, 2
• Chronic hypernatremia: limit correction to 10-15 mmol/L per 24 hours 6, 1

The rationale: brain cells synthesize intracellular osmolytes over 48 hours to adapt to hyperosmolar conditions; rapid correction causes water influx and cerebral edema 6

Fluid Selection Based on Volume Status

Hypovolemic Hypernatremia:

• Administer hypotonic fluids to replace free water deficit 6, 3
• Options include: 0.45% NaCl (77 mEq/L sodium), 0.18% NaCl (31 mEq/L sodium), or D5W 6
• Never use isotonic saline (0.9% NaCl) as initial therapy—it delivers excessive osmotic load requiring 3 liters of urine to excrete the load from just 1 liter infused, worsening hypernatremia 6
• D5W is preferred as it delivers no renal osmotic load and allows controlled decrease in plasma osmolality 6

Euvolemic Hypernatremia (Diabetes Insipidus):

• Central DI: desmopressin (Minirin) is the primary treatment 1
• Nephrogenic DI: requires ongoing hypotonic fluid administration to match excessive free water losses 6
• Low salt diet (<6 g/day) and protein restriction (<1 g/kg/day) may be beneficial 6

Hypervolemic Hypernatremia:

• In cirrhosis: discontinue IV fluids and implement free water restriction, focusing on negative water balance 6
• In heart failure: sodium and fluid restriction (1.5-2 L/day), with vasopressin antagonists (tolvaptan, conivaptan) considered for short-term use in persistent severe cases with cognitive symptoms 6

Initial Fluid Administration Rates

For adults: 25-30 mL/kg/24 hours 6

For children:

• First 10 kg: 100 mL/kg/24 hours
• 10-20 kg: 50 mL/kg/24 hours
• Remaining weight: 20 mL/kg/24 hours 6

Special Clinical Scenarios

Severe hypernatremia with altered mental status:

• Combine IV hypotonic fluids with free water via nasogastric tube 6
• Target correction: 10-15 mmol/L per 24 hours 6

Nephrogenic diabetes insipidus:

• Avoid isotonic saline entirely—it will worsen hypernatremia 6
• Requires continuous hypotonic fluid replacement to match ongoing losses 6

Acute hypernatremia (<24 hours) with severe symptoms:

• Hemodialysis is an effective option to rapidly normalize sodium levels 1
• When starting renal replacement therapy in chronic hypernatremia, avoid rapid sodium drops 1

Monitoring Requirements

Essential monitoring during treatment: 6, 4

• Serum sodium, potassium, chloride, bicarbonate levels
• Renal function and urine osmolality
• Neurological status for signs of cerebral edema
• Fluid balance and body weight

Common Pitfalls to Avoid

• Correcting chronic hypernatremia too rapidly causes cerebral edema, seizures, and neurological injury 6
• Using isotonic saline in patients with renal concentrating defects exacerbates hypernatremia 6
• Failing to address underlying cause while correcting sodium levels 3, 4
• Inadequate monitoring during correction increases risk of complications 1