HYPONATREMIA

HYPONATREMIA Step 1: Is this TRUE hyponatremia? Check plasma osmolality: Posm low → True Hyponatremia Posm normal or high → Pseudo-Hyponatremia Causes: Hyperglycemia Hypertriglyceridemia Paraproteinemia Mannitol True Hyponatremia Is ADH appropriately suppressed? Check urine osmolality: Urine osmolality < 100 → ADH suppressed Causes: Polydipsia Insufficient osmole intake Urine osmolality > 100 → ADH present Why is ADH present? Check clinical volume status: Volume Status Categories Hypovolemic Renal (UNa > 20, FeNa > 1%) Osmotic diuresis (e.g., Diabetic Ketoacidosis*) Hypoaldosteronism Diuretics Polyuric Acute Tubular Necrosis Extra renal (UNa < 10, FeNa < 1%) GI losses (gastroenteritis*) Renal losses (especially thiazide diuretics) Insensible losses (Cystic Fibrosis*, Burns*) Bleeding Euvolemic SIADH (e.g., pain/post-op, neurologic trauma, drugs, pulmonary pathology, malignancy) Endocrinopathies (hypothyroidism) Adrenal insufficiency Pregnancy Hypervolemic Low intravascular volume (↓EABV) (Low UNa esp. < 20): Congestive heart failure* Nephrotic syndrome* Nephritic syndrome* Sepsis* with capillary leak High intravascular volume (↑EABV) (UNa > 20, FeNa > 1%): Renal Failure* Serum sodium correction in hyperglycemia: [Na⁺] corrected=[Na⁺]+(0.3×([glucose]−5))\text{[Na⁺] corrected} = \text{[Na⁺]} + (0.3 \times (\text{[glucose]} - 5)) [Na⁺] corrected=[Na⁺]+(0.3×([glucose]−5)) *Indicates Key Condition This is not an exhaustive list of medical conditions.