Electrolytes are positively or negatively charged particles that readily dissolve in water. The predominant positively charged electrolytes in the body are sodium, potassium, calcium, and magnesium, while negatively charged electrolytes include chloride, phosphates, and bicarbonate.
Description
Salts are chemical compounds composed of atoms that carry electrical charges. Dissolved in water, the components in a salt exist as ions. Collectively, these ions are called electrolytes. Electrolytes are dissolved in different compartments of body water including: the serum portion of the blood, inside the cells (intracellular), and out-side the cells (extracellular). The concentration of these electrolytes varies considerably from one area to the other. However, there is a narrow concentration limit of these electrolytes that the body must maintain within each of these compartments. The body transfers electrolytes intracellularly and extracellularly as required to maintain electrolyte balance. Electrolyte concentrations of extracellular fluid can be measured in a blood sample.
Function
The kidney filters electrolytes in blood and maintains a balance by excreting the proper amount in the urine. An electrolyte's concentration in a solution of dissolved salts can be measured as the amount in milliequivalents (mEq) per volume of solution (i.e. per liter). Electrolytes have many functions and roles in the body. The concentration of electrolytes must be maintained within a narrow range within the blood, otherwise deleterious physiological effects may occur. Several of the most important electrolytes will be discussed individually in the following sections.
Sodium balance
HYPONATREMIA. The most common electrolyte disorder is hyponatremia, it occurs in almost 1% of all patients hospital admissions. Hyponatremia is a condition characterized by low sodium in the blood, below 136 mEq per liter of blood. In hyponatremia, the sodium concentration has been overdiluted by an excess of water or a loss of sodium in the body. Hyponatremia may result from intraveous administration of water to hospitalized patients or can also occur with small amounts of water consumption in those who have impaired kidney function and several other conditions such as liver cirrhosis, heart failure, underactive adrenal glands as with Addison's disease, and various antidiuretic hormone disorders. Over 50% of hospitalized patients with AIDS have been reported to suffer from hyponatremia. Lethargy and confusion are typically the first signs of hyponatremia. Muscle twitching and seizures may occur as hyponatremia progresses with risk of stupor, coma, and death in the most severe cases. Due to the effects on the central nervous system, mortality risk is considerably greater in acute hyponatremia than in chronic hyponatremia. Other factors that reduce survival are the presence of debilitating illnesses such as alcoholism, hepatic cirrhosis, heart failure, or malignancy.
HYPERNATREMIA. Hypernatremia is a condition characterized by a high concentration of sodium in the blood, above 145 mEq per liter of blood. There is too little water compared to the amount of sodium in the blood, often resulting from a low intake of water. Profuse sweating, vomiting, fever, diarrhea, or abnormal kidney function may result in hypernatremia. With age, there is a decreased thirst sensation; therefore, hypernatremia is more common in the elderly. Aging reduces the kidney's ability to concentrate urine; therefore, taking diuretics may further exacerbate hypernatremia. Hypernatremia is very serious, particularly in the elderly. Almost half of individuals hospitalized for this condition will die, although it is often secondary to other illnesses.
Major causes of high sodium levels include:
limited water access, particularly when combined with any other cause
excess water loss due to profuse sweating, vomiting, fever, diarrhea
disorders of other electrolytes
head trauma or neurosurgery involving the pituitary gland
As with hyponatremia, the major symptoms of hypernatremia result from brain dysfunction. Severe hypernatremia can lead to confusion, muscle twitching, seizures, coma, and death. The effects on central nervous system hyperosmolality and the seriousness of the under-lying illness lead to greater mortality in acute hypernatremia compared to chronic hypernatremia.
Calcium balance
HYPOCALCEMIA. A low calcium blood level is referred to as hypocalcemia. Calcium is measured in extracellular fluid in two forms: total calcium concentration and ionized calcium concentration. About 50% of the total calcium concentration in the plasma exists in ionized form, which is the form that has biological activity at cell membranes. The remainder is either bound to the plasma proteins (about 40%) or complexed in the non-ionized form (about 10%) with anions such as phosphate. In hypocalcemia the total calcium concentration falls below 2.4 mEq/l in the extracellular fluid. Hypocalcemia can result from a number of problems. The most common reason is an inability to mobilize calcium from the bones or a chronic loss of calcium in the urine.
An abnormally low blood calcium concentration may not produce any symptoms. However, over time the lack of calcium in the blood can affect brain function causing neurologic symptoms such as memory loss, depression, confusion, delirium, and hallucinations. Once calcium levels return to normal, these symptoms are reversible. Very severe cases of hypocalcemia can lead to seizures, tetany, and muscle spasms in the throat, affecting breathing. The condition is usually first discovered during routine blood tests because often there are no symptoms evident.
HYPERCALCEMIA. A high calcium blood level is referred to as hypercalcemia. The blood calcium concentration rises above 10.5 mg per deciliter of blood. Increased gastrointestinal tract absorption or increased intake of calcium may lead to hypercalcemia. Individuals who consume large amounts of calcium or who take calcium containing antacids can develop hypercalcemia. Absorption of calcium can be increased in the gastrointestinal tract with an overdose of vitamin D. The condition is usually first discovered during routine blood tests because hypercalcemia often doesn't have any symptoms at all.
If symptoms occur, typically the earliest are:
constipation
loss of appetite
nausea and vomiting
abdominal pain
Large amounts of urine may be produced by the kidneys. Due to excess urine production, fluid levels in the body decrease and may lead to dehydration. Severe hypercalcemia may induce brain dysfunction symptoms such as weakness, confusion, emotional disturbances, delirium, hallucinations, and coma. Additionally, abnormal heart rhythms and death may follow. In chronic conditions, kidney stones or calcium-containing crystals that can cause permanent damage may form.
Potassium balance
HYPOKALEMIA. A low potassium blood level is referred to as hypokalemia. It occurs when the blood potassium concentration falls below 3.8 mEq per liter of blood. Hypokalemia is common in the elderly. Common causes include decreased intake of potassium during acute illness, nausea and vomiting, and treatment with thiazide or loop diuretics. About 20% of patients receiving thiazide diuretics develop hypokalemia, which is dose-dependent but usually mild. Since several foods contain potassium, hypokalemia is not typically due to a low intake. It is usually due to malfunction of the kidneys or abnormal loss through the gastrointestinal tract. People with heart disease have to be especially cautious regarding hypokalemia (particularly when taking digoxin), because they are prone to developing abnormal heart rhythms.
Potassium usually can be replaced relatively easily by eating foods rich in potassium or by taking potassium salts (potassium chloride) orally.
HYPERKALEMIA. A high level of potassium in the blood is referred to as hyperkalemia. It occurs when the blood potassium concentration rises above 5.0 mEq per liter of blood. Hyperkalemia typically results when the kidneys excrete too little potassium.
Antidiuretic hormone (ADH)—A hormone that encourages the kidney to retain water when body stores are low.
Bicarbonate—A salt of carbonic acid produced by neutralizing a hydrogen ion.
Dehydration—A deficit of body water that results when the output of water exceeds intake.
Diuretic—An agent or drug that eliminates excessive water in the body by increasing the flow of urine.
Edema—An increase in blood volume instigates an accumulation of extracellular fluid resulting in swelling of the feet, ankles, and lower legs.
Electrolyte—A substance such as an acid, bases, or salt. An electrolyte's water solution will conduct an electric current and ionizes. Acids, bases, and salts are electrolytes.
Homeostasis—An organism's regulation of body processes to maintain internal equilibrium in temperature and fluid content.
Hypoparathyroidism—A condition resulting from an absence or deficiency in parathyroid hormone. It is characterized by hypocalcemia and hyperphosphatemia.
Tetany—A general stiffening and spasms of the muscles that can occur in severe cases of hypocalcemia.
a sudden release of potassium from the cell reservoir in such cases as when a large amount of muscle tissue is destroyed (crush injury) or severe burn injuries, or an overdose on crack cocaine
The kidney's ability to excrete potassium is over-whelmed due to a rapid influx into the blood, resulting in life-threatening hyperkalemia. Generally, hyperkalemia is more dangerous than hypokalemia. A blood potassium concentration above 5.5 mEq/liter starts to affect the electrical conducting system in the heart. If the concentration continues to increase, the heart rhythm becomes irregular which may cause the heart to eventually stop.
Mild hyperkalemia often may not produce any symptoms. Symptoms may include an irregular heartbeat that could be experienced as palpitations. Hyperkalemia is typically first diagnosed during a routine blood test or by examining changes in an electrocardiogram. Severe deficiencies may lead to muscular weakness, twitches, and paralysis.
Magnesium balance
HYPOMAGNESEMIA. A low level of magnesium in the blood is known as hypomagnesemia. The level of magnesium in the blood decreases below 1.6 mEq per liter of blood. Metabolic and nutritional disorders are usually the culprit of hypomagnesemia, most often when intake of magnesium is decreased during starvation or intestinal malabsorption compounded with greater kidney excretion.
Symptoms of hypomagnesemia may include:
loss of appetite
nausea and vomiting
sleepiness
weakness
personality changes
muscle spasms
tremors
When hypomagnesemia occurs along with hypocalcemia, the magnesium must be replaced before successful treatment of the calcium disorder.
HYPERMAGNESEMIA. A high level of magnesium in the blood is referred to as hypermagnesemia. The blood magnesium concentration rises above 2.1 mEq per liter of blood. Hypermagnesemia is quite rare unless people with kidney failure are given magnesium salts or consume magnesium-containing drugs such as antacids. Weakness, low blood pressure, and impaired breathing can result and the heart may stop if the concentration increases above 12 to 15 mEq per liter.
Phosphate regulation
Phosphorus occurs in the body almost solely in the form of phosphate, which is composed of one phosphorus and four oxygen atoms. Phosphate is found mostly in bones, although a significant amount is found intracellularly. It plays a role in energy metabolism and acid-base regulation, and it is used as a building block for DNA. Phosphate is excreted in the urine and stool.
Sources of phosphate include:
spinach, turnip greens, collard greens, kale, and other green leafy vegetables
Speakman, Elizabeth and Weldy, Norma Jean. Body Fluids and Electrolytes 8th ed. London: Mosby Incorporated, 2001.
Workman, M. Linda Introduction to Fluids, Electrolytes and Acid-Base Balance London: W B Saunders Co., 2001.
PERIODICALS
Beck, L.H. "The aging kidney. Defending a delicate balance of fluid and electrolytes." Geriatrics 55, no. 4 (2000): 26-28, 31-32.
Sawka, M. N., and S. J. Montain. "Fluid and electrolyte supplementation for exercise heat stress." American Journal of Clinical Nutrition 72, 2 suppl., (2000): 564S-572S.
OTHER
Nr-Space, et al. Fluids & Electrolytes CD-ROM. Delmar Publishers, 2001.
