The normal concentration of sodium in the blood plasma is 136-145 mM. If thesodium level falls too late, it's called hyponatremia; if it gets too high, it's called hypernatremia.
A sodium level in the blood that is too low is dangerous and can cause seizures and coma. Very high sodium levels can lead to seizures and death.
Sodium is a mineral element and an important part of the human body. It controls the volume of fluid in the body and helps maintain the acid-base level. About 40% of the body's sodium is contained in bone, some is found within organs and cells and the remaining 55% is in blood plasma and other fluids outside cells. Sodium is important in proper nerve conduction, the passage of various nutrients into cells, and the maintenance of blood pressure.
The body continually regulates its handling of sodium. When a person eats toomuch or too little sodium, the intestines and kidneys respond to adjust concentrations to normal. During the course of a day, the intestines absorbs dietary sodium while the kidneys excrete a nearly equal amount of sodium into theurine.
The concentration of sodium in the blood depends on the total amount of sodium and water in arteries, veins, and capillaries (the circulatory system). Thebody regulates sodium and water in different ways, but uses both to help correct blood pressure when it is too high or too low.
If the body has too little sodium (called hyponatremia), the body can eitherincrease sodium levels or decrease water in the body. Too high a concentration of sodium (hypernatremia), can be corrected either by decreasing sodium orby increasing body water.
There are many diseases that can cause abnormal salt levels, including diseases of the kidney, pituitary gland, and hypothalamus. This is especially a concern in elderly patients, who have a harder time regulating the concentrations of various nutrients in the bloodstream.
Low salt levels can be caused by eating too little salt or excreting too muchsodium or water, and by diseases that impair the body's ability to regulatesodium and water. Keeping to a low-salt diet for many months or sweating toomuch during a race on a hot day, can make it hard to keep sodium levels highenough. While these conditions alone aren't likely to cause loss salt levels,it can occur under special circumstances. For example, patients taking diuretic drugs who eat a low-sodium diet may have hyponatremia. term="Diuretics" type="print-hyplink" >Diuretic drugs can correct high blood pressure by helping the body get rid of sodium into the urine -- but excreting too much sodiumcan cause hyponatremia. Usually only mild hyponatremia occurs in patients taking diuretics. However, sodium levels can fall dangerously low in patients who eat a low-sodium diet and drinking too much water. Severe and prolonged diarrhea also can cause low sodium levels. A person with severe diarrhea can lose large amounts of water, sodium, and various nutrients. Some diarrheal diseases release especially large amounts of sodium and are most likely to cause hyponatremia. Drinking too much water may cause low sodium levels, because when the water is absorbed into the blood, it can dilute the sodium. This causeof hyponatremia is rare, but has been found in mentally ill patients who compulsively drink more than 20 liters of water a day. Excessive drinking of beer, which is mostly water without much sodium, can also produce hyponatremia when combined with a poor diet.
Marathon running under certain conditions can lead to hyponatremia, since sweat contains both sodium and water. Studies show that about 30% of marathon runners experience mild hyponatremia during a race. However, drinking water during a race isn't the answer -- this can lead to severe hyponatremia because the drinking water dilutes the sodium in the bloodstream. Such runners may experience brain problems as a result of the severe hyponatremia and require emergency treatment.
Hyponatremia also develops from disorders in organs that control the body's regulation of sodium or water. The adrenal gland secretes a hormone that travels to the kidney, where it prompts the kidney to retain sodium by not excreting it into the urine. Addison's disease, which damages the adrenal gland, cantherefore lead to low levels of sodium in the body.
The hypothalamus and pituitary gland are also involved in sodium regulation by making and releasing vasopressin, known as the anti-diuretic hormone, intothe bloodstream. Vasopressin prompts the kidneys to reduce the amount of water released into urine. If the body produces too much vasopressin, it promptsthe body to conserve water, causing a lower concentration of sodium in the blood. In addition, certain types of cancer cells produce vasopressin, which also can lead to hyponatremia. If the body produces too little vasopressin, thebody doesn't conserve enough water and the level of sodium in the body rises.
High sodium levels may occur in diabetes insipidus, a disease that causes toomuch urine to be produced. In this type of diabetes, either the hypothalamusfails to make vasopressin, or the kidneys don't respond to vasopressin. In either case, the kidney is able to regulate the body's sodium levels, but can't retain water. High sodium levels don't occur in diabetes insipidus if the patient is able to drink enough water to keep up with urinary loss, which maybe as high as 10 liters per day.
Sodium levels may rise in unconscious patients because they can't drink water. Water is continually lost by evaporation from the lungs and in the urine; if the patient isn't given water intravenously, the sodium concentration in the blood may increase and hypernatremia could develop. Hypernatremia can alsooccur in rare diseases in which the thirst impulse is impaired. Hypernatremiaalso can occur accidentally in the hospital when patients are given solutions containing sodium.
Symptoms of high sodium levels can include confusion, coma, paralysis of thelung muscles, and death. The severity of the symptoms is related to how quickly the high sodium levels developed. If the levels build up suddenly, the brain cells can't adapt to their new high-sodium environment. Hypernatremia is especially dangerous for children and the elderly. Moderately low sodium levels may trigger fatigue, confusion, headache, muscle cramps, and nausea. Severehyponatremia can lead to seizures and coma.
Abnormal sodium levels are diagnosed by measuring the concentration of sodiumin the blood. In low sodium levels, unless the cause is obvious, a variety of tests are needed to determine if sodium was lost from the urine, diarrhea,or from vomiting. Tests are also used to determine hormone problems. The patient's diet and use of diuretics must also be considered.
Severely low sodium levels can be treated by giving intravenous sodium and water into the blood. Moderate hyponatremia due to use of diuretics or high levels of vasopressin is often treated by drinking less water each day. Hyponatremia due to an abnormal adrenal gland is treated with hormone injections. High sodium level is treated with an intravenous solution of water a normal concentration of sodium. The infusion is performed over many hours or days to prevent abrupt and dangerous changes in brain cell volume. In emergencies, suchas when a high sodium level is causing brain symptoms, infusions may be conducted with half the normal concentration of salt.
A low sodium level is just one manifestation of a variety of disorders. Whileit can easily be corrected, the prognosis for the underlying condition thatcauses it varies. The prognosis for treating a high sodium level is excellent, unless neurological symptoms are severe or if a doctor tries to reverse thecondition too quickly.
It is not always easy to prevent abnormal salt levels. Patients who take diuretic medications must be checked regularly for the development of hyponatremia. High levels occur only in unusual circumstances that are not normally under a person's control.