Physiology of Serum Sodium

Composition of Serum

  • Serum Water: accounts for 93% of the serum volume
    • Serum sodium is restricted to the serum water fraction
  • Nonaqueous Components: accounts for 7% of the serum volume
    • Nonaqueous components are mainly lipids and proteins

Etiology of Hypernatremia

Water Loss Alone

Renal Water Loss

Extra-Renal Water Loss

  • Fever (see Fever, [[Fever]]): insensible water loss from skin
  • Burns (see Burns, [[Burns]]): insensible water loss from skin
  • Hyperventilation: insensible water loss from lungs

Water + Sodium Loss

Renal Water + Sodium Loss

  • Chronic Kidney Disease (CKD) (see Chronic Kidney Disease, [[Chronic Kidney Disease]]): osmotic diuresis
  • Hyperglycemia (see Hyperglycemia, [[Hyperglycemia]]): osmotic diuresis
  • Mannitol (see Mannitol, [[Mannitol]]): osmotic diuresis

Extra-Renal Water + Sodium Loss

  • Sweating/Diaphoresis (see Diaphoresis, [[Diaphoresis]])

Sodium Gain

Excessive Sodium Administration

Adrenal Hyperfunction

Diagnosis of Hypernatremia

  • Serum Sodium

Laboratory Serum Sodium Measurement Technology

  • Flame Photometry Assay of Serum Sodium: measures sodium concentration in whole plasma
    • In the presence of hyperproteinemia or hyperlipidemia (with expansion of nonaqueous component of the serum), pseudohyponatremia may be seen with this assay method
  • Sodium-Selective Electrode Assay of Sodium: measures sodium activity in serum water -> this assay gives the true, physiologically relevant sodium concentration as it measures sodium activity in serum water alone
    • Indirect Potentiometry: current assay used in many hospital laboratories
    • Direct Potentiometry

Clinical Manifestations

Neurologic Manifestations

  • Ataxia (see Ataxia, [[Ataxia]])
  • Encephalopathy/Altered Mental Status
  • Irritability
  • Reversible Splenial Lesion Syndrome (RESLES) (see Reversible Splenial Lesion Syndrome, [[Reversible Splenial Lesion Syndrome]])
  • Seizures (see Seizures, [[Seizures]])
  • Spasticity
  • Thirst
  • Tremor (see Tremor, [[Tremor]])

Other Manifestations

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  • xxxx
  • xxxx
  • xxxx


General Treatment Considerations

  • Calculate Free Water Deficit = (0.6) x (Wt in kg) x ((Serum Na/140)-1)
    • Note: total body water = 0.6 x BW in kg
  • Correct serum Na at <1 mEq/L per hr
  • Replace 50% of free water deficit over first 24 hrs, then rest over next 48 hrs

Treatment by Type

  • Hypovolemic: NS until euvolemic, then D5W
  • Hypervolemic: Lasix (or HD) + D5W
  • Central Diabetes Insipidus
    • Pitressin (see xxxx, [[]]: 2.5 U IM q48hrs
    • Desmopressin (DDAVP) (see Desmopressin, [[Desmopressin]]): 10-20 ug qday intranasal
  • Nephrogenic Diabetes Insipidus
    • xxx


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