hyponatremi

Hyponatremia refers to a serum sodium concentration below 135 milliequivalents per liter (mEq/L). It is a common electrolyte disorder that can range from mild to life-threatening, depending on the acuity and underlying cause.

Hyponatremia is usually divided by tonicity: hypotonic hyponatremia, the most common form; hypertonic hyponatremia, caused by high osmolal substances such as glucose; and pseudohyponatremia, a laboratory artifact in severe hyperlipidemia or hyperproteinemia.

Common causes include syndrome of inappropriate antidiuretic hormone secretion (SIADH) from lung disease, CNS disorders, or certain drugs; volume depletion with loss of Na and water; heart failure, cirrhosis, and nephrotic syndrome; renal disease; adrenal insufficiency and hypothyroidism; primary polydipsia and excessive water intake.

Symptoms are variable and can be nonspecific. Mild cases may be asymptomatic. Acute or severe hyponatremia can cause confusion, headache, nausea, vomiting, seizures, and coma due to cerebral edema.

Evaluation includes measurement of serum osmolality, urine osmolality and urine sodium, assessment of volume status, and testing for contributing conditions such as thyroid and adrenal function and hyperglycemia to distinguish hyponatremia types.

Management depends on severity, duration, and cause. Severe or life-threatening hyponatremia with neurologic symptoms is treated with hypertonic saline (3%) carefully given as small boluses with frequent monitoring to avoid rapid overcorrection. In patients at risk of overcorrection, desmopressin may be used to pace correction. Less urgent cases favor fluid restriction and treating the underlying disorder.

Overly rapid correction carries risk of osmotic demyelination syndrome; target no more than about 8 to 10 mEq/L increase in the first 24 hours in most patients, with careful monitoring. Chronic hyponatremia often requires slower correction.