Hypernatremia

Hypernatremia or hypernatraemia (see American and British English spelling differences) is an electrolyte disturbance that is defined by an elevated sodium level in the blood. Hypernatremia is generally not caused by an excess of sodium, but rather by a relative deficit of free water in the body. For this reason, hypernatremia is often synonymous with the less precise term, dehydration.

Water is lost from the body in a variety of ways, including perspiration, insensible losses from breathing, and in the feces and urine. If the amount of water ingested consistently falls below the amount of water lost, the serum sodium level will begin to rise, leading to hypernatremia. Rarely, hypernatremia can result from massive salt ingestion, such as may occur from drinking seawater.

Ordinarily, even a small rise in the serum sodium concentration above the normal range results in a strong sensation of thirst, an increase in free water intake, and correction of the abnormality. Therefore, hypernatremia most often occurs in people such as infants, those with impaired mental status, or the elderly, who may have an intact thirst mechanism but are unable to ask for or obtain water.

Signs and symptoms
Clinical manifestations of hypernatremia can be subtle, consisting of lethargy, weakness, irritability, and edema. With more severe elevations of the sodium level, seizures and coma may occur.

Severe symptoms are usually due to acute elevation of the plasma sodium concentration to above 158 mEq/L (normal is typically about 135-145 mEq/L). Values above 180 mEq/L are associated with a high mortality rate, particularly in adults. However such high levels of sodium rarely occur without severe coexisting medical conditions.

Cause
Common causes of hypernatremia include:


 * Hypovolemic
 * Inadequate intake of water, typically in elderly or otherwise disabled patients who are unable to take in water as their thirst dictates. This is the most common cause of hypernatremia.
 * Excessive losses of water from the urinary tract, which may be caused by glycosuria, or other osmotic diuretics.
 * Water losses associated with extreme sweating.
 * Severe watery diarrhea
 * Euvolemic
 * Excessive excretion of water from the kidneys caused by diabetes insipidus, which involves either inadequate production of the hormone, vasopressin, from the pituitary gland or impaired responsiveness of the kidneys to vasopressin.
 * Hypervolemic
 * Intake of a hypertonic fluid (a fluid with a higher concentration of solutes than the remainder of the body). This is relatively uncommon, though it can occur after a vigorous resuscitation where a patient receives a large volume of a concentratedsodium bicarbonate solution. Ingesting seawater also causes hypernatremia because seawater is hypertonic.
 * Mineralcorticoid excess due to a disease state such as Conn's syndrome or Cushing's Disease

Treatment
The cornerstone of treatment is administration of free water to correct the relative water deficit. Water can be replaced orally or intravenously. Water alone cannot be administered as intravenously (because of osmolarity issue) rather can be given with addition to dextrose or saline infusion solutions. However, overly rapid correction of hypernatremia is potentially very dangerous. The body (in particular the brain) adapts to the higher sodium concentration. Rapidly lowering the sodium concentration with free water, once this adaptation has occurred, causes water to flow into brain cells and causes them to swell. This can lead to cerebral edema, potentially resulting in seizures, permanent brain damage, or death. Therefore, significant hypernatremia should be treated carefully by a physician or other medical professional with experience in treatment of electrolyte imbalances.