hyponatræmi

Hyponatræmi is a condition in which the serum sodium concentration is below 135 mmol/L. It is the most common electrolyte disorder encountered in clinical practice and may be acute (developing within hours) or chronic (lasting days to weeks). Symptoms range from none to life-threatening, depending on the magnitude and rate of sodium decline.

Classification of hyponatræmi is typically by extracellular fluid volume status. Hypovolemic hyponatræmi involves loss of salt and water with impaired free water excretion, as seen with gastrointestinal losses or diuretic use. Euvolemic hyponatræmi features normal fluid volume with inappropriately concentrated urine, most commonly due to SIADH, but also from hypothyroidism or adrenal insufficiency. Hypervolemic hyponatræmi occurs when there is excess total body water relative to sodium, as in heart failure, cirrhosis, or nephrotic syndrome. Numerous drugs, including thiazide diuretics, antidepressants, antipsychotics, and NSAIDs, can contribute to hyponatræmi.

Diagnosis relies on a structured work-up. Measure serum osmolality to identify hypotonic hyponatræmi and exclude pseudohyponatremia or hypertonic hyponatremia (for example, due to severe hyperglycemia). Determine urine osmolality and urine sodium to differentiate causes. Assess thyroid and adrenal function, review current medications, and evaluate volume status.

Management depends on symptoms and chronicity. Severe symptomatic hyponatræmi (confusion, seizures, coma) is treated with hypertonic saline (3% NaCl) given as a controlled bolus with close monitoring. Hypovolemic hyponatræmi is usually treated with isotonic saline, while euvolemic or hypervolemic cases are managed with fluid restriction and treatment of the underlying disorder; vasopressin receptor antagonists may be considered in select SIADH cases. The rate of correction must be carefully limited to avoid osmotic demyelination syndrome, typically not exceeding 8–10 mmol/L in 24 hours and 18 mmol/L in 48 hours, with adjustments for individual risk factors.

Prognosis varies with cause, duration, and the success of safe correction; hyponatræmi is associated with higher morbidity and mortality in hospitalized patients.