SIADH

Pt with h/o cerebral tumor presents with new onset hyponatremia s/p surgery. Symptoms of fever, headache, neck stiffness, SOB additionally concerning for pneumonia, meningitis. Medications include amiodarone, carbamazepine, chlorpromazine, SSRI. Denies use of diuretics, Ecstasy. Does not eat low salt diet. Fever, MMM, nuchal rigidity, pulmonary crackles, euvolemia on exam.

  • Labs

    • Serum mOsm: [(Na x 2) + (glucose / 18) + (BUN / 2.8)] < 280

    • Urine Na > 40 mEq/L and urine osmolality > 100 mOsm/kg

    • Serum BUN:Cr ratio, TSH within normal limits

    • Urine drug screen negative

  • Trial of 1L NS

    • SIADH indicated by decreased sodium levels s/p bolus

    • If urine Na > 40 mEq/L or urine Osm < 100 mOsm/kg s/p bolus, reconsider hypovolemic hyponatremia

  • Imaging

    • U/S shows no IVC collapse (euvolemic)

    • Consider CXR to evaluate for pneumonia

  • Treatment

    • D/c medications associated with SIADH

    • Fluid restrict to 1.5L daily

    • If no improvement with fluid restriction

      1. Obtain ACTH stimulation test to r/o adrenal insufficiency

      2. ACTH stimulation test negative for adrenal insufficiency: Obtain renal consult and consider starting vaptans

  • Pt counseled that long-term control may require loop diuretics and high salt diet

 

Notes

  • Diuretic use and low sodium diets can complicate differentiating between hypovolemic and euvolemic hyponatremia

  • Conditions commonly associated with SIADH

    • Surgery

    • Pneumonia

    • CNS insults (e.g. tumor, meningitis)

  • Other euvolemic hyponatremia etiologies include hypothyroidism, adrenal insufficiency, Ecstasy use