Definition for Hyponatremia

Hypolimnion

Hypoosmotic

A metabolic condition in which there is not enough sodium (salt) in the body fluids outside the cells (serum sodium is less than 136 meq/L). Clinical indicators and treatment depend on the cause of hyponatremia and whether or not it is associated with a normal, decreased or increased ECF volume.

Signs and Symptoms

Neurologic symptoms usually do not occur until the serum sodium level has dropped to approximately 120-125 meq/L. Hyponatremia with decreased ECF volume: irritability, apprehension, dizziness, postural hypotension, dry mucus membranes, cold and clammy skin, tremors, seizures. Hyponatremia with normal or increased ECF volume: headache, lassitude, apathy, confusion, weakness, edema, weight gain, elevated blood pressure, muscle cramps, convulsions.

History and Risk Factors

Diarrhea, fistulas, vomiting, NG suction, diuretics, adrenal insufficiency, skin losses (burns, wound drainage), other. Note: hyperlipidemia, hyperproteinemia, and hyperglycemia may cause a pseudo-hyponatremia. This must be ruled out before determining therapy. For every 100 mg/dl increase in glucose, the sodium is diluted by 1.6 meq/L.

Diagnostic Tests

Serum sodium will be less than 136 meq/L. Serum osmolality will be decreased except in cases of pseudo-hyponatremia, azotemia, or toxins that increase osmolality (example: ethanol). Urine specific gravity will be decreased because of the kidneys attempt to excrete excess water. Urine sodium: decreased (except in SIADH and adrenal insufficiency).

Collaborative Management

The goal of therapy is to get the patient out of immediate danger (eg return the sodium level to greater than 120 meq/L) and then gradually return the serum sodium to a normal level and restore normal ECF volume.