Hypovolemic Hypernatremia

Aka: Hypovolemic Hypernatremia, Hypernatremia with Decreased Total Body Sodium

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II. Pathophysiology

  1. Hypovolemia with Decreased Total Body Sodium (but extracellular Hypernatremia)

III. Causes: 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

IV. Causes: 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

V. 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
      1. Chronic Hypernatremia (>48 hours) should be replaced slowly (esp. in under age 30-40 years)
      2. Limit Serum Sodium reduction to 12 mEq/L per day
    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. Delivery
      1. Enteral water sources are preferred (e.g. Feeding Tube)
      2. D5W is an alternative (avoid 1/2NS due to risk of volume overload)
    5. Monitor Electrolytes closely while administering D5W
      1. Serum Sodium
      2. Serum Osmolality
        1. Do not decrease faster than 1-2 mOsm/kg water/hour
    6. Initial: Restore extracellular fluid volume to correct Hypotension
      1. Administer Normal Saline (0.9%)
    7. Next: Correct Serum Sodium
      1. Administer free water as above
  3. Treat underlying renal causes
    1. Losses from fever or Mechanical Ventilation
  4. Treat underlying renal causes
    1. Central Diabetes Insipidus
      1. Replace ADH (Desmopressin)
    2. Nephrogenic Diabetes Insipidus
      1. Treat primary problem (e.g. withdraw offending agent)

VI. References

  1. Braun (2015) Am Fam Physician 91(5): 299-307 [PubMed]

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