Hypernatremia

Aka: Hypernatremia, High serum sodium

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II. Definitions

  1. Hypernatremia
    1. Serum Sodium exceeds 145 meq/liter

III. Epidemiology

  1. Incidence: 1% of hospitalized elderly patients

IV. Pathophysiology

  1. Free water deficient state
    1. Total Body Water deficit > Total Body Sodium Deficit
    2. Excess water loss or rarely excess Sodium intake or Sodium retention
  2. Lacks normal physiologic response to free water loss
    1. Inability to concentrate urine or inadequate ADH secretion
    2. Lack of thirst response or inadequate access to free water

V. Findings: Signs and Symptoms

  1. Infants
    1. Tachypnea
    2. Muscle Weakness
    3. Motor restlessness
    4. High pitched crying
    5. Lethargy
    6. Coma
  2. Adults
    1. Anorexia
    2. Nausea or Vomiting
    3. Muscle Weakness
    4. Lethargy
    5. Restlessness
    6. Hyperreflexia
    7. Spasticity
    8. Seizures

VI. Causes

  1. See specific types below
  2. Hypernatremia with Polyuria in hospitalized patients is common
    1. Results from Parenteral or enteral feeds AND
    2. Inadequate free water intake OR Increased free water loss (e.g. Central Diabetes Insipidus in Head Injury)

VII. Types: Based on Volume Status

  1. Hypervolemic Hypernatremia
    1. Hypernatremia with Increased Total Body Sodium
  2. Isovolemic Hypernatremia
    1. Hypernatremia with Normal Total Body Sodium
  3. Hypovolemic Hypernatremia
    1. Hypernatremia with Decreased Total Body Sodium

VIII. Labs (Dependent on Hypernatremia subtype as above)

  1. Serum labs
    1. Serum Sodium >145 mEq/L
      1. Severe symptoms occur at >160 mEq/L
    2. Serum Glucose
    3. Serum Calcium
    4. Serum Creatinine and Blood Urea Nitrogen
  2. Urine labs
    1. Urine Volume
    2. Urine Sodium
    3. Urine Potassium
    4. Urine Chloride
    5. Urine Calcium
  3. Calculations based on above
    1. Serum Osmolality
    2. Free Water Deficit
    3. Serum to urine Electrolyte ratio
      1. Urine Electrolytes: Urine Sodium + Urine Potassium
      2. Serum Electrolytes: Serum Sodium + Serum Potassium
      3. Interpretation (question whether Kidney is excreting or retaining Electrolyte-free water)
        1. Concentrated urine: Urine Electrolytes exceed serum Electrolytes
        2. Dilute urine: Serum Electrolytes exceed urine Electrolytes

IX. Management

  1. See specific Hypernatremia types based on fluid status
  2. See Hypervolemic Hypernatremia
  3. See Isovolemic Hypernatremia
  4. See Hypovolemic Hypernatremia

X. Complications of cerebral Dehydration

  1. Cerebral Hemorrhage
    1. Subarachnoid Hemorrhage
    2. Subcortical Hemorrhage
  2. Venous sinus thrombosis

XI. Prognosis: Mortality

  1. Children
    1. Acute Hypernatremia: 43%
    2. Chronic Hypernatremia: 7-29%
  2. Adults
    1. Acute Hypernatremia: 60%

XII. References

  1. Braun (2015) Am Fam Physician 91(5): 299-307 [PubMed]
  2. Miller (2023) Am Fam Physician 108(5): 476-86 [PubMed]

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