Sodium  (Na +) is an important (mineral) electrolyte for the transmission of signals between cells as well as for its functioning, being more abundant in extracellular fluids. Na + is also important in regulating water inside and outside the cells.
What is hyponatremia?
Hyponatremia is the medical term used when blood Na + levels are below normal, that is, below 135 mEq/L  (<135 mmol/L). In clinical practice, it constitutes the most frequent change in electrolytes.
Hyponatremia is a water imbalance, with a relative excess of body water in relation to the sodium value. It is usually associated with a disturbance in the hormone that regulates the water balance, vasopressin (also called antidiuretic hormone). In people with this problem, caused by one or more factors, the body conserves too much water which will cause a dilution of Na + in the blood.
Hyponatremia can also occur due to increased body loss of Na+. It can be classified according to the duration of Na+ reduction: acute when the time duration is less than 48 hours or chronic when hyponatremia has existed for more than 48 hours.