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What is Hyponatremia?

Hyponatremia is a condition in which the sodium levels in the blood get reduced.

Clinically it is defined as plasma sodium levels lower than 135mEq/L.

Understanding Hyponatremia

All body cells require sodium for better functioning and equilibrium. Hence, the levels are very tightly maintained between 135-145mEq/L. The most sensitive cells to get affected by any fluctuation of sodium are the brain cells (neurons).

Since brain cells now face an imbalance of sodium on their outside compared to their insides, the cells try to re-attain equilibrium by moving water into the cell.

In the early phase, when sodium outside the cell is less than the usual concentration, the cell is placed in a dilute medium that is in excess of water. Water, therefore, moves into the cells causing them to swell. It happens to all the body’s cells but neurons are especially sensitive to this change.

If the imbalance persists for a long duration, i.e. days and weeks, the cells adapt by losing organic molecules from their insides and thus tries to get rid of the extra water that was needed to keep them dissolved.

Types of Hyponatremia

Depending upon the clinical status of blood volume it is categorized into three types:

  1. Hypovolemic (Decreased blood volume of body)
  2. Hypervolemic (Increased blood volume of body)
  3. Euvolemic/normovolemic (no change in blood volume of body)

What are the symptoms of Hyponatremia?

  1. Early symptoms: Nausea, headache, vomiting
  2. Muscle cramps
  3. Weakness and fatigue
  4. Mental confusion and disorientation
  5. Convulsions
  6. Coma

What are the risk factors for Hyponatremia?

  1. Patients who have been started on Thiazide group of anti-hypertensives (drugs for hypertension)
  2. Endocrine disorders (hormone imbalances)
  3. Drug abuse
  4. As a consequence of a medical intervention
    • Colonoscopy preparation
    • Prostate surgery
    • Uterine surgery
    • Hypotonic fluid administration

What are the causes of Hyponatremia?

  1. Kidney diseases: When kidney loses its function of water and sodium balance, especially in aging kidney. Kidney failure is also one of the important causes of Hyponatremia
  2. Hormonal Imbalances: Deficiency of Mineralo-corticoid hormone (produced by adrenal glands) can lead to excess loss of sodium in urine. Syndrome of inappropriate anti-diuretic hormone (SIADH) in pituitary gland dysfunction. Hypothyroidism (reduction in thyroid hormone), Gluco-corticoid hormone deficiency (produced by adrenal glands)
  3. Liver diseases: Cirrhosis of liver
  4. Heart failure
  5. Elderly patients undergoing surgical procedures like:
  6. Stress
  7. Hypotonic fluid administration

What are the complications with Hyponatremia?

Neurological complications remain the main complications.

  1. Convulsions
  2. Coma
  3. Death

How is Hyponatremia diagnosed?

Plasma sodium concentration <130mEq/L

Urine sodium concentration

  1. Hypovolemic Hyponatremia : < 20M/L
  2. Hypervolemic Hyponatremia : > 30mM/L
  3. Euvolemic/normovolemic Hyponatremia 20-30 mM/L

What is the treatment for Hyponatremia?

  1. Identification of the cause and treatment of the same
  2. Restriction of fluid intake
  3. Correction with 3% hypertonic solution (saline concentrated with sodium) with a diuretic to add sodium and remove only the water
  4. Vasopressin (V2 receptor) antagonists

In long standing Hyponatremia, rapid correction is not advocated as the brain cells are adapted to a new steady state and rapid correction could lead to loss of more water from the cells leading to dehydrated neurons.

Also Read: All About Hypernatremia

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