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

• Central Diabetes Insipidus (DI) (see Diabetes Insipidus, [[Diabetes Insipidus]])
  • Hypothalamic Infiltration
  • Pituitary-Hypothalamic Surgery
  • Head Trauma (see Head Trauma, [[Head Trauma]])
  • Phenytoin (Dilantin) (see Phenytoin, [[Phenytoin]])
  • Encephalitis (see Encephalitis, [[Encephalitis]])
• Nephrogenic Diabetes Insipidus (DI) (see Diabetes Insipidus, [[Diabetes Insipidus]])
  • Sarcoidosis (see Sarcoidosis, [[Sarcoidosis]])
  • Amyloidosis (see Amyloidosis, [[Amyloidosis]])
  • Hypercalcemia (see Hypercalcemia, [[Hypercalcemia]])
  • Hypokalemia (see Hypokalemia, [[Hypokalemia]])
  • Lithium (see Lithium, [[Lithium]])
  • Cisplatin (see Cisplatin, [[Cisplatin]])

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

• Hypertonic Saline (see Hypertonic Saline, [[Hypertonic Saline]])
• Normal Saline (see Normal Saline, [[Normal Saline]])
• Sodium Bicarbonate (see Sodium Bicarbonate, [[Sodium Bicarbonate]])
• Sodium Chloride (NaCl) (see Sodium Chloride, [[Sodium Chloride]])

Adrenal Hyperfunction

• Hyperaldosteronism (see Hyperaldosteronism, [[Hyperaldosteronism]])
• Cushing Syndrome (see Cushing Syndrome, [[Cushing Syndrome]])

---

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
  • Delirium (see Delirium, [[Delirium]])
  • Lethargy
  • Obtundation-Coma (see Obtundation-Coma, [[Obtundation-Coma]])
• 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

• xxxx
• xxxx
• xxxx
• xxxx

---

Treatment

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

---

References

• xxx