Sodium imbalance
Sodium is the major cation (90%) in extracellular fluid; potassium, the major cation in intracellular fluid. During repolarization, the sodium-potassium pump continually shifts sodium into the cells and potassium out of the cells; during depolarization, it does the reverse.
Sodium cation functions include maintaining tonicity and concentration of extracellular fluid, acid-base balance (reabsorption of sodium ions and excretion of hydrogen ions), nerve conduction and neuromuscular function, glandular secretion, and water balance.
The body requires only 2 to 4 g of sodium daily. However, most Americans consume 6 to 10 g daily (mostly sodium chloride, as table salt), excreting excess sodium through the kidneys and skin.
A low-sodium diet or excessive use of diuretics may induce hyponatremia (decreased serum sodium concentration); dehydration may induce hypernatremia (increased serum sodium concentration).
Causes
Sodium imbalance can result from several causes.
Hyponatremia
One of the main causes of hyponatremia is excessive GI loss of water and electrolytes. This can result from vomiting, suctioning, or diarrhea; excessive perspiration or fever; potent diuretics; or use of tap-water enemas.
When such losses decrease circulating fluid volume, increased secretion of antidiuretic hormone (ADH) promotes maximum water reabsorption, which further dilutes serum sodium. These factors are especially likely to cause hyponatremia when combined with too much electrolyte-free water intake.
Excessive drinking of water, infusion of I.V. dextrose in water without other solutes, malnutrition or starvation, and a low-sodium diet can also cause hypo-natremia, usually in combination with one of the other causes.
Trauma, surgery (wound drainage), and burns, which cause sodium to shift into damaged cells, can lead to decreased serum sodium levels, as can adrenal gland insufficiency (Addison’s disease), hypoaldosteronism, and cirrhosis of the liver with ascites.
Syndrome of inappropriate antidiuretic hormone secretion (SIADH), resulting from brain tumor, cerebrovascular accident, pulmonary disease, or neoplasm with ectopic ADH production, can lead to hyponatremia also. Certain drugs, such as chlorpropamide
and clofibrate, may produce an SIADH-like syndrome.
and clofibrate, may produce an SIADH-like syndrome.
Clinical effects of sodium imbalance
| System | Hyponatremia | Hypernatremia |
|---|
