II. Type: Renal Sodium Loss (impaired renal concentrating ability)

  1. Findings
    1. Urine Osmolality 300-600 mOsm/kg
    2. Urine Sodium >20 meq/liter
  2. Causes (Hypotonic polyuria)
    1. Diuretics
    2. Interstitial Nephritis (Nephrogenic DIabetes)
    3. High urine flow states
    4. Severe protein malnutrition
    5. Hypokalemia
    6. Hypercalcemia
    7. Osmotic diuresis (usually results in Hyponatremia)
      1. Hyperosmolar nonketotic coma
      2. Glycosuria (excess Urine Glucose)
      3. Mannitol
      4. Postobstructive diuresis
      5. Enteral Feedings
    8. Non-oliguric Acute Tubular Necrosis (ATN) - recovery phase

III. Type: Extra-renal Sodium Loss

  1. Findings
    1. Urine Osmolality >600-800 mOsm/kg water
    2. Urine Sodium <10-20 meq/liter
  2. Causes
    1. Gastrointestinal losses
      1. Vomiting
      2. Osmotic Diarrhea
      3. Nasogastric suction
    2. Respiratory losses
    3. Skin losses
    4. Heat Illness
    5. Adrenal Insufficiency

IV. Management

  1. Reverse underlying causes (especially renal underlying causes)
  2. Sodium correction (moderate to severe Hypernatremia)
    1. Calculate Free Water Deficit
    2. Replace Free Water Deficit with D5W over 48 hours
    3. Correction rate
      1. Acute: 1 mEq/hour
      2. Chronic: 0.5 mEq/hour (do not decrease Sodium >8-10 mEq in 24 hours)
    4. Monitor electrolytes closely while administering D5W
      1. Serum Sodium
      2. Serum Osmolality
        1. Do not decrease faster than 1-2 mOsm/kg water/hour
    5. Initial: Restore extracellular fluid volume
      1. Administer Normal Saline (0.9%)
    6. Next: Correct Serum Sodium
      1. Administer half Normal Saline (0.45%)

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