SIADH

Key considerations: Cerebral salt wasting (vs SIADH — volume status differentiates), Adrenal insufficiency, Hypothyroidism causing hyponatremia

Cannot miss

history: Medications (SSRIs, carbamazepine, NSAIDs), pulmonary symptoms, neurologic symptoms, malignancy history; exam: Volume status assessment (euvolemic in SIADH), neurologic exam, signs of hypothyroidism/adrenal insufficiency; labs: Serum osmolality (low <280), urine osmolality (>100 mOsm/kg), urine sodium (>40 mEq/L), TSH, cortisol, BMP; imaging: Chest imaging (malignancy/pulmonary cause); Head CT/MRI if CNS cause suspected; bedside: Serum sodium, volume status assessment

immediate: Severe (Na <120 or symptomatic): 3% hypertonic saline 1-2 mL/kg/hr; Correct no faster than 8 mEq/L in 24 hours (10-12 if active seizures); general: Fluid restriction 800-1000 mL/day first line; Treat underlying cause; Vaptans (tolvaptan) for chronic SIADH if fluid restriction fails; Salt tablets and loop diuretics as adjunct

admit: Na <125 or symptomatic, requires IV hypertonic saline; discharge: Mild chronic hyponatremia with identified cause and outpatient follow-up; consults: Endocrinology, nephrology for refractory cases

Overcorrection of hyponatremia causes osmotic demyelination syndrome (central pontine myelinolysis) — irreversible
If overcorrecting, give free water or DDAVP to slow correction rate
SIADH is euvolemic — if the patient appears hypovolemic, consider cerebral salt wasting instead