hypernatremia

Etiology

• excessive loss of free water (most common)
  • sweating - fever
  • diarrhea
  • diuretics concurrent with fluid restriction
  • osmotic diuresis
    • glucose
    • urea
    • mannitol
  • diabetes insipidus
    • nephrogenic diabetes insipidus
    • central diabetes insipidus
    • gestational diabetes insipidus
  • loss of urine-concentrating ability
    • polyuric phase of acute tubular necrosis (ATN)
    • postobstructive uropathy
    • hypercalcemia
    • hypokalemia
  • lack of thirst
• excessive sodium intake
  • incorrect reconstitution of infant formula
  • high osmolar enteral feedings
  • use of NaHCO3 in cardiopulmonary resuscitation
  • hypertonic diasylate
  • table salt ingestion
• hypothalamic dysfunction (impaired pituitary secretion of ADH)
  • impaired thirst (older nursing home residents)
  • congenital lesions
  • neoplasms
  • granulomatous disease: sarcoidosis
  • trauma
  • central diabetes insipidus
• shift in hypotonic water from intracellular to extracellular space
  • vigorous exercise
  • seizures
  • mild hypernatremia
• adrenal hyperfunction
  • Cushing's disease
  • primary hyperaldosteronism
  • mild hypernatremia
• predisposing factors
  • renal insufficiency
  • dementia
  • ischemic heart disease
  • pneumonia
  • sepsis
  • cardiac dysrhythmia
  • anemia
  • hypertension
  • congestive heart failure (CHF)
  • stroke

Pathology

• hyperosmolarity
• total body water loss
• blunted thirst mechanism or inability to ingest water sufficient to replenish losses
• impaired pituitary secretion of ADH

Clinical manifestations

• symptoms appear with [Na+] > 155-160 meq/L
• central nervous system
  • lethargy
  • muscle weakness
  • confusion
  • seizures & irritability in infants
  • intracerebral or subarachnoid hemorrhage
    • rupture of cerebral veins secondary to changes in brain volume
  • coma
  • death
• thirst may go unrecognized secondary to decreased state of consciousness
• symptoms related to rate of change of sodium concentration
  • acute hypertonicity leads to neuronal shrinkage
  • during chronic hypernatremia, cellular adaptation occurs
• signs of dehydration
  • hypotension
  • tachycardia
  • poor skin turgor
  • sunken eyes
  • may not be recognized in the elderly
• generally associated with systemic disorder

Laboratory

• serum chemistries
  • electrolytes
• appropriate tests for underlying systemic disorder
• free water deficit = total body water x (140/Na+ - 1)
  • total body water in liters = 0.6 x weight in kg
• free water clearance (in liters)
  • urine volume x (1 - (urine Na+ + urine K+)/serum Na+)
• urine osmolality
  • maximally concentrated with inadequate water intake
    • in the elderly, this may be only 600-800 mosm/kg (500-700)
  • inappropriately dilute urine in patients with renal water loss (i.e diabetes insipidus, hyperglycemia of diabetes mellitus)
• lumbar puncture
  • increased CSF protein
  • few if any WBC in CSF
  • not necessarily indicated

Complications

• cerebral edema & seizures may occur with excessively rapid correction of hypernatremia
• survivors often show neurologic sequelae

Management

• correct hypernatremia over 48-72 hours
  • acute hypernatremia may be treated more rapidly
    • 5% dextrose titrated to serum sodium of 140-145 meq/L over 24 hours
  • add free water deficit + free water clearance + 10 mL/kg/day to determine water deficit (see Laboratory above)
  • rate of correction < 0.5 meq/l/hour
  • time period necessary to correct free water deficit: (measured [Na+] - desired [Na+]) / 0.5 meq/L/hr
  • no more than 1/2 of the calculated water deficit should be given in the 1st 24 hours
  • < 10 meq/L should be corrected in the 1st 24 hours to prevent cerebral edema
• replacement fluids
  • correct hypovolemia (hypotension) with normal saline or lactated ringers
  • hypotonic fluids appropriate after hypovolemia (hypotension) corrected
    • water
    • D5W
    • 1/2 normal saline
  • generally decreased level of consciousness dictates IV replacement
  • replacement may be oral if patient is awake
  • water treatment of choice orally or by NG-tube
• hypotensive or tachycardic patient
  • normal saline or lactated ringers may be used initially
• frequent electrolyte measurements to determine response to therapy
• diabetes insipidus (impaired pituitary secretion of ADH) is treated with desmopression (intranasal or oral)

More general terms

• electrolyte disorder
• sign/symptom

Additional terms

• hyponatremia
• sodium (Na+) in serum