Nephrology Book

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HyponatremiaAka: Low Serum Sodium

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  1. Definition
    1. Serum Sodium < 135 meq/L
  2. Pathophysiology
    1. Hypoosmolar Hyponatremia is most common
    2. Sodium is the principal osmole
    3. Hyponatremia is a water excess state
  3. Symptoms: Acute Hyponatremia (develops over <24 hours)
    1. Symptom onset when Serum Sodium <125 meq/L
    2. Initial
      1. Nausea
      2. Vomiting
      3. Headache
    3. Later or Severe (Serum Sodium <120 meq/L)
      1. Seizure
      2. Coma
      3. Respiratory arrest
  4. Symptoms: Chronic Hyponatremia (develops over >48 hours)
    1. Lethargy
    2. Confusion
    3. Muscle cramps
    4. Neurologic Impairment
  5. Prognosis: Mortality
    1. Acute Hyponatremia (Serum Sodium <120 meq/L): 50%
      1. Mortality associated with cerebral edema
    2. Chronic Hyponatremia: 10%
      1. Mortality associated with underlying condition
  6. Approach
    1. Is patient hypervolemic?
      1. See Hypervolemic Hypoosmolar Hyponatremia
    2. Measure Serum Osmolarity
      1. Hyperosmolar Hyponatremia (Serum Osms >300)
      2. Hypoosmolar Hyponatremia (Serum Osms <280)
        1. Hypovolemic Hypoosmolar Hyponatremia
        2. Isovolemic Hypoosmolar Hyponatremia
        3. Hypervolemic Hypoosmolar Hyponatremia
      3. Normoosmolar Hyponatremia (Serum Osms 280-300)
  7. Management
    1. See specific Hyponatremia protocols based on Serum Osms
    2. See Hyponatremia Management
  8. References
    1. Kone in Tisher (1993) Nephrology, p. 87-100
    2. Levinsky in Wilson (1991) Harrison's IM, p. 281-84
    3. Rose (1989) Acid-Base and Electrolytes, p. 601-38

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