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Hyponatremia is defined as a serum sodium concentration below 135 mEq/L and represents the most common electrolyte disorder in hospitalized patients. It can range from asymptomatic to life-threatening, with symptoms primarily related to cerebral edema and neurological dysfunction.
Hyponatremia results from an imbalance between water intake and excretion, leading to excess free water relative to sodium. The primary mechanism involves either excessive water retention (often due to inappropriate ADH secretion), inadequate water excretion, or true sodium loss with inadequate replacement, causing cellular swelling particularly in the brain.
Clinical assessment focuses on determining the patient's volume status (hypovolemic, euvolemic, or hypervolemic) and symptom severity to guide treatment approach. Rapid correction should be avoided in chronic cases due to risk of osmotic demyelination syndrome, while acute symptomatic hyponatremia may require immediate intervention with hypertonic saline to prevent cerebral herniation.