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Hyponatremia
(Low Sodium)

Hyponatremia (Low Sodium) Overview

Sodium and water levels in the body are tightly regulated to keep it functioning normally. Sodium concentration is higher in the bloodstream than inside cells. Regulatory mechanisms help control and maintain sodium levels. The hormones aldosterone (made in the adrenal gland) and anti-diuretic hormone (ADH) or vasopressin (made in the pituitary) adjust the way the kidneys deal with water and sodium to maintain the appropriate total amount of sodium and water in the body.

Water in the body is closely linked to the location of sodium in the body. If the concentration of sodium is too high in the bloodstream, water will leak from cells into the blood stream to try to dilute and lower the sodium concentration. Conversely, if sodium levels in the bloodstream are too low, water will leave the blood and enter cells, causing them to swell.

Hyponatremia is the term used to describe low sodium levels in the bloodstream (hypo=low + natr=sodium + emia=blood). Acute hyponatremia describes the situation in which sodium levels drop quickly, while chronic hyponatremia describes situations with a gradual fall in the sodium concentrations over days or weeks. Chronic hyponatremia is often well tolerated since the body has a chance to adapt.

Neurologic changes are the most concerning consequence of hyponatremia. Cerebral edema (excess fluid in the brain, leading to swelling) may occur with severe or acute hyponatremia. Water enters the brain cells causing them to swell. Because the brain is enclosed in a bony skull that cannot expand, the brain is compressed since there is no room for swelling to occur. As a result, brain function may be compromised significantly.