water across membranes affects the concentration of sodium in the blood. Sodium acts as a force that pulls water across membranes, and water moves from places with lower sodium concentration to places with higher sodium concentration. This happens through a process called osmosis. When evaluating sodium imbalances, both total body water and total body sodium must be considered. Hypernatremia Hypernatremia means that the concentration of sodium in the blood is too high. An individual is considered to be having high sodium at levels above 145 mEq/L of sodium. Hypernatremia is not common in individuals with no other health concerns. Most individuals with this disorder have either experienced loss of water from diarrhea, altered sense of thirst, inability to consume water, inability of kidneys to make concentrated urine, or increased salt intake. Causes There are three types of hypernatremia each with different causes. The first is dehydration along with low total body sodium. This is most commonly caused by heatstroke, burns, extreme sweating, vomiting, and diarrhea. The second is low total body water with normal body sodium. This can be caused by diabetes insipidus, renal disease, hypothalamic dysfunction, sickle cell disease, and certain drugs. The third is increased total body sodium which is caused by increased ingestion, Conn's syndrome, or Cushing's syndrome. Symptoms Symptoms of hypernatremia may vary depending on type and how quickly the electrolyte disturbance developed. Common symptoms are dehydration, nausea, vomiting, fatigue, weakness, increased thirst, excess urination. Patients may be on medications that caused the imbalance such as diuretics or nonsteroidal anti-inflammatory drugs. Some patients may have no obvious symptoms at all. Treatment It is crucial to first assess the stability of the patient. If there are any signs of shock such as tachycardia or hypotension, these must be treated immediately with IV saline infusion. Once the patient is stable, it is important to identify the underlying cause of hypernatremia as that may affect the treatment plan. The final step in treatment is to calculate the patients free water deficit, and to replace it at a steady rate using a combination of oral or IV fluids. The rate of replacement of fluids varies depending on how long the patient has been hypernatremic. Lowering the sodium level too quickly can cause cerebral edema. Hyponatremia Hyponatremia means that the concentration of sodium in the blood is too low. It is generally defined as a concentration lower than 135 mEq/L. This