A client has a serum sodium level of 125 mEq/L (normal 135-145 mEq/L). Which clinical manifestations does the nurse MOST anticipate?

HYPONATREMIA is defined as serum sodium below 135 mEq/L. Normal: 135-145 mEq/L. A value of 125 mEq/L is SIGNIFICANTLY LOW. PATHOPHYSIOLOGY: sodium is the primary extracellular osmole; when sodium drops, serum osmolality drops; water moves by osmosis from the low-sodium ECF INTO cells (following osmotic gradient); BRAIN CELLS SWELL → neurological symptoms are the hallmark. CLINICAL MANIFESTATIONS based on severity and rate of onset: MILD (130-135 mEq/L): may be asymptomatic or have nausea, headache, malaise; MODERATE (125-130 mEq/L): headache, nausea, vomiting, lethargy, confusion, muscle cramps; SEVERE (<125 mEq/L): seizures, coma, respiratory arrest, death. RATE MATTERS: ACUTE hyponatremia (rapid drop) is more dangerous than chronic hyponatremia (brain has had time to adapt). CAUSES: HYPERVOLEMIC (too much water, normal sodium): heart failure, cirrhosis, nephrotic syndrome, SIADH; HYPOVOLEMIC (lost sodium and water, but more sodium than water): GI losses, diuretics, adrenal insufficiency; EUVOLEMIC: SIADH (syndrome of inappropriate antidiuretic hormone secretion — common cause; ADH causes water retention without sodium retention; causes: malignancy, CNS disorders, medications); water intoxication (rare). CONTRAST WITH HYPERNATREMIA (high sodium, >145 mEq/L): extreme thirst, dry mucous membranes, fever, decreased urine output, concentrated urine, confusion, seizures (cells shrink); treated with free water replacement. TREATMENT OF HYPONATREMIA: depends on cause and severity; mild-moderate: fluid restriction (for SIADH); replace sodium if depleted; CAUTION: correct SLOWLY (no more than 8-12 mEq/L per 24 hours) — rapid correction causes OSMOTIC DEMYELINATION SYNDROME (ODS, formerly central pontine myelinolysis) — irreversible brain damage. PN ROLE: monitor serum electrolytes; observe for neurological changes; report confusion or seizures immediately; measure I&O; implement fluid restriction if ordered.