Hypernatremia: Causes, Pathophysiology

It has a serum sodium concentration of more than 145mEq/L. Nelson also accepts that in certain institutions or countries, serum sodium ≥150mEq/L is taken to be Hypernatremia. Normal Serum Na⁺  Concentration is 135- 145 mEq/L

Causes of Hypernatremia 

1. Severe dehydration may lead to more water or electrolyte-based fluid intake.
2. High Salt intake
3. Other endocrine disorders
4. In children, it is due to improper maternal milk production & poor formula milk preparation.

Pathophysiology of Hypernatremia

Other Medical conditions may cause Hypernatremia.

·  Central DI

·  Nephrogenic DI 

Differential Diagnosis for Hypernatremia

·  Hyperosmolar Hyperglycemic Non ketogenic coma

Diagnostics

 Serum Sodium Levels – More than 170 in DI & Dehydration may show around 150.

CT or MRI   shows bridging veins and sinus due to movement of fluid from the brain, & Brain shrinkage can lead to intracranial hemorrhage, often seen in subdural space.

Other lab tests

· Water Deprivation test, ADH Stimulation test

Treatment of Hypernatremia

• If it is acute, severe Hypernatremia, usually secondary to sodium administration, it can be corrected more rapidly with 5% dextrose in water (D5W) because idiogenic osmoles have not had time to accumulate. Fluid cannot be given if there is acute severe Hypernatremia with volume overload. So, a trial of loop diuretics like furosemide will be given intravenously. If furosemide is not adequate, these patients usually need to be managed by dialysis. In the case of chronic Hypernatremia, it is usually corrected very slowly. The target is the correction of <10mEq/L in 24 hours and the overall therapy should take around 2-4 days.
• No aggressive therapy needs to be given for hyperglycemia or hypocalcemia
• Treat the underlying cause

Treatment Of Hypernatremic Dehydration

• Restoring intravascular volume
  • Normal saline is given as a relatively slow bolus – 20ml/kg is given over 20 min. No more than two boluses should be given.
• Correction of serum sodium
  • Determine the time for correction based on initial sodium concentration.
    • If the serum sodium is between 145-157mEq/L – correct the sodium level within 24 hrs.
    • If the serum sodium is 158-170mEq/L – correct the sodium level over 48 hrs.
    • If the serum sodium is 171-183mEq/L – correct the sodium level over 72 hrs.
    • If the serum sodium is 184-196mEq/L – correct the sodium level over 84 hrs.
• The commonly used fluid available in all the wards is N/2 in 5% dextrose. The requirement will be 1.25-1.5 times the maintenance. The slow correction needs to be done. When corrections are made, the ongoing losses will be replaced.
• Monitor serum sodium every 4 hours. When correcting the serum sodium, it should not fall by >0.5mEq/L/h (the upper limit). If the serum sodium decreases too rapidly, either reduce the fluid rate or increase the sodium concentration in the fluid. This will ensure that the rate becomes controlled rather than being too rapid. If the serum sodium decreases too slowly, either increase the fluid rate or reduce the sodium concentration, making it even more hypotonic.
• Suppose there are any features of decreased intravascular volume. During the correction, if it is developing, another normal saline bolus of 20ml/kg can be considered. If seizures happen, rapid correction should be done. Rapidly restore the serum sodium level to safe levels and 3% hypertonic saline @ 4-6ml/kg IV over 30 min should be given.

Emergency Treatment

• Hypernatremia should not be corrected more than one mEq/L per hr
• Monitor patient's blood pressure, and CNS imaging should be considered in order of treatment protocol
• Free water deficit =Body weight (kgs)x percentage of total body water (TBW)Serum Na/140)-1}
• Patients with renal failure may be under dialysis for fluid balance & sodium

Frequently Asked Questions

1. What is the drug of choice in fluid over load in hypernatremia ?

Ans. Furosemide

2) what is the fluid of choice in hypernatremia ?

Ans. 5% dextrose

3) Which is a common cause of hypernatremia?

Ans. Diabetes Insipidus

Also Read: NEET PG High Yield Questions for Physiology

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