Hypernatremia (Na >145 mEq/L) is usually related to abnormalities in aldosterone, sodium transport in the kidney, anti-diuretic hormone (ADH) or thirst and consumption of fluids.

The 6 categories of causes of hypernatremia are:

1. Inadequate Fluid Intake compared to Fluid Losses
2. Primary Hypodipsia
3. Diabetes Insipidus
4. Pure Hypertonic Saline Gain
5. Endocrine causes (primary hyperaldosteronism, Cushing's syndrome)
6. Other [osmotic diuresis (hyperglycemia, mannitol), post urinary obstruction diuresis or hypertonic dialysis]

Clinically, symptoms may include:

• Absence of symptoms
• Altered level of consciousness
• Ataxia
• Coma/Lethargy
• Hyperreflexia
• Irritability
• Spasticity
• Twitching

The usual goals of therapy are to treat dehydration (initially using 0.9% Saline) and once dehydration is adequately addressed, replace the free water deficit gradually (usually over 48-72 hours, with ½ being replaced over the first 12-24 hours and the remainder thereafter with goal of serum sodium decreasing NO FASTER than 1 mEq/L/hr) with careful monitoring. Most clinicians replace the water deficit with D5W given IV or with oral fluids if tolerated.

The Free Water Deficit (FWD) in liters is Calculated by:

• FWD = [(Serum Sodium - 140)/140] × Body Weight in Kgs × Fraction TBW

Fraction TBW Table

Note that too rapid a correction of hypernatremia may result in cerebral edema.

References:

1. Kugler JP, Hustead T. Hyponatremia and Hypernatremia in the Elderly. Am Fam Physician . 2000;61(12):3623-3630.
2. Rosen's Emergency Medicine: Concepts and Clinical Practice , 5th ed.
3. Ferri's Clinical Advisor: Instant Diagnosis and Treatment, 2005 ed.
4. Clinical Procedures in Emergency Medicine, 4th ed.