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]])
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
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
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
References