ELECTROLYTES

ELECTROLYTES. Electrolytes are molecules that, in solution, dissociate into positively charged ions (cations) and negatively charged ions (anions). Principal ions in body fluids are sodium, potassium, and chloride. A 70 kg adult has a body content of approximately 100 g sodium, 140 g potassium, and 95 g chloride. To maintain a stable body content, the amount of principal ions lost must equal the amount consumed. During growth and during pregnancy, the amount accreted for tissue formation also must be considered.

Physiological Functions

Sodium is the predominant cation in fluids outside the cells (extracellular fluid), whereas potassium is the predominant cation in the intracellular fluid. Chloride is the major anion of the extracellular fluid. Sodium plays a central role in regulating body fluid balance and distribution of fluid between the extracellular and intracellular compartments. As sodium is the major osmotically active particle in the extracellular fluid, sodium and its accompanying anion determines the osmolar concentration, or osmolarity, of this compartment. An increase in sodium concentration will increase the osmolarity of the extracellular fluid, thus causing water to move out of the cells into the extracellular compartment. It will also cause water retention by stimulating the thirst mechanism and by decreasing urine flow. The opposite occurs when sodium concentration is decreased. Thus, sodium plays a central role in regulating body fluid balance and the distribution of fluid between the extracellular and intracellular compartments.

Potassium is necessary for normal growth and plays an important function in cell metabolism, enzyme reactions, and synthesis of muscle protein. Both sodium and potassium are involved in maintaining proper acidity (pH) of the blood and in maintaining nerve and muscle functions. Normal resting membrane potentials of nerve and muscle cells range between –50 and 100 mV, with the inside of the cells negative with respect to the outside. These resting membrane potentials are maintained by the chemical gradient of potassium across cell membranes. Activation of excitable cells alters their membrane permeabilities to sodium and potassium, leading to changes in their membrane potentials. A weak stimulus causes a small depolarization (the inside of the cell is made less negative) as a result of sodium influx along its electrochemical gradient via the voltage-gated sodium channels in cell membranes. This is followed by repolarization, which is a manifestation of potassium efflux. If the stimulus is sufficiently strong, large changes in the membrane potential occur, during which the membrane potential may change from –70 mV to +30 mV, and then repolarize back to its resting membrane potential. This action potential, cause by alternation of potassium steady-state potentials with pulsed sodium potentials, gives rise to a traveling wave of depolarization that is conducted along the nerve fiber to exert an effect on the effector cells it innervates (supplies with nerves). In muscles, action potential leads to muscle contraction.

Dietary sodium chloride in foods and beverages is absorbed mostly in the small intestine. Active transport of sodium out of the small intestinal epithelial cells across their basolateral membrane provides an electrochemical gradient for the absorption of sodium across the luminal membrane. Entry of sodium through carrier proteins can either transport other solutes against their concentration gradient in the same direction (co-transport) or in an opposite direction (counter-transport). A number of transporters have receptor sites for binding sodium and glucose, galactose, or amino acids. Therefore, entry of sodium across the luminal membrane also brings in a solute. Counter-transport mechanisms operating in the kidneys allow excess hydrogen and potassium to be excreted in the urine.

Consumption of Sodium, Chloride, and Potassium

Consumption usually exceeds the needs of an individual, although the amount consumed varies widely with dietary habits. Most natural foods contain high potassium content but are lower in sodium content (Table 1). American adults consume an average of 2.5 to 3.5 g of potassium daily. Individuals consuming large amounts of fruits and vegetables may have a daily intake of as high as 11 g. Sodium is consumed mainly as sodium chloride (table salt). A small amount is consumed as sodium carbonate, sodium citrate, and sodium glutamate. Intakes of sodium vary, averaging 2 to 5 g/day of sodium or 5 to 13 g/day of sodium chloride. Only about 10 percent of sodium intake is from natural foods, the rest from sodium salts added during cooking and at the table, and from salts added during processing of foods. In regions where consumption of salt-preserved foods is customary, intake of sodium can be as high as 14 to 20 g/day.

Under normal circumstances, about 99 percent of dietary sodium, chloride, and potassium is absorbed. Absorption occurs along the entire length of the intestine, the largest fraction being absorbed in the small intestine and the remaining 5 to 10 percent in the colon. Potassium is also secreted in the colon. Various homeostatic regulatory mechanisms, the most important of which is aldosterone, modulate the absorption of sodium and secretion of potassium.

Loss of Sodium, Chloride, and Potassium

Obligatory loss of fluids through skin, urine, and feces invariably causes loss of these ions. Minimal obligatory loss for an adult consuming average intakes has been estimated to be 115 mg/day for sodium and 800 mg/day for potassium. Over 95 percent of loss is in the urine. Under most circumstances, loss of chloride parallels that of sodium. Loss of these ions can increase greatly in diuresis, vomiting, and diarrhea. Loss of sodium chloride can also increase greatly from profuse sweating.

Recommended Intake. Daily minimum needs can be estimated from the amount required to replace obligatory

losses (Table 2). The need is increased in infants and children, and during pregnancy and lactation. Estimated safe minimum intake levels are higher than the minimum requirements to account for the various degrees of physical activity of individuals and environmental conditions. Average intakes in the United States are higher than the estimated safe minimum levels of sodium chloride (1.3 g/day) and potassium (2 g/day).

The association of high salt intake with hypertension and the beneficial effects of potassium in hypertension has led to recommendations that daily intake of salt should not exceed 6 g and that of potassium should be increased to 3.5 g. This can be achieved by increasing intake of dietary fruits and vegetables.

Regulation of Sodium, Chloride, and Potassium Balance

Various mechanisms regulate excretion of these ions by the kidneys to maintain homeostatic equilibrium of body fluids. Urinary sodium excretion is controlled by varying the rate of sodium reabsorption from the glomerular filtrate by tubular cells, whereas potassium excretion is controlled by varying the rate of tubular secretion of potassium.

Abnormally low blood volume (hypovolemia) in sodium deficit increases renal sodium chloride reabsorption by increasing sympathetic discharge to the kidneys, and by stimulation of two hormonal systems, the renin-angiotensin-aldosterone and the antidiuretic systems. This results in the production of low urine volume with low sodium and chloride contents. Hypovolemia also initiates the thirst mechanism and increases an appetite for salt (or salt cravings).The presence of salt appetite in animals is to ensure an adequate intake of salt to protect the extracellular fluid volume from excessive loss of sodium due to sweating, diarrhea, pregnancy, or lactation. The development of salt appetite is of significance in the successful adaptation to a terrestrial life, especially in herbivorous animals. The need for salt can be satisfied by providing cattle and sheep with salt licks. Humans and other carnivores are less dependent on separate supplies of salt because dietary salt can be obtained from meat. However, they may develop a craving for salt when they are sodium deficient. This deficit-induced salt craving may be mediated by hormones acting on the brain and by changes in gustatory response. Abnormally high blood volume (hypervolemia) in sodium excess increases renal excretion of sodium chloride by suppression of sympathetic discharge to the kidneys, suppression of the renin-angiotensin-aldosterone and antidiuretic systems, and stimulation of the secretion of atrial natriuretic peptides.

Aldosterone is the most important hormone regulating secretion of potassium. Aldosterone secretion is triggered by angiotensin II, by high plasma potassium concentration, or by low plasma sodium concentration. Plasma concentrations of potassium and hydrogen also affect directly the secretion of potassium by the distal nephrons. The rate of potassium secretion parallels the plasma potassium concentration. Secretion of potassium in response to changes in acid-base balance (which affects plasma pH) is complex. In general, acute acidosis decreases secretion of potassium, whereas acute alkalosis increases secretion and loss of potassium from the body. Response to chronic acid-base disorders is varied.

Sodium, Chloride, and Potassium Imbalance

Acute excessive intakes do not normally result in retention of sodium, chloride, and potassium because of the capacity of the kidneys to excrete these ions. Retention occurs when kidney function is compromised. Dietary deficiency does not normally occur because normal consumption usually exceeds body needs.

Since the extracellular fluid volume changes in parallel with its sodium concentration, sodium retention in renal failure or congestive heart failure results in edema and possibly hypertension (Table 3). Excessive loss of sodium resulting in hypovolemia and hypotension can occur through diuresis, Addison's disease, severe vomiting, or diarrhea.

Changes in plasma concentration of potassium affects the excitability of nerves and muscle cells (Table 3). Retention of potassium causes hyperkalemia (plasma potassium concentration exceeding 5.0 mmol/l), and depletion causes hypokalemia (plasma potassium concentration less than 3.5 mmol/l). Retention of potassium occurs when there is a lack of aldosterone secretion, or a lack of responsiveness of the kidney to aldosterone. An important clinical manifestation of hyperkalemia is cardiac arrhythmia, which can lead to cardiac arrest. Depletion of potassium can occur through hyperaldosteronism, diuresis,

vomiting, or diarrhea. Manifestations of hypokalemia include depressed neuromuscular functions and, in more severe hypokalemia, cardiac arrhythmias.

Nutritional Considerations

Epidemiological and experimental evidence has implicated habitual high dietary salt consumption in the development of hypertension, but controversy remains regarding the importance of sodium salts in the regulation of blood pressure and the mechanisms by which salt influences blood pressure (Stamler, 1977). Intervention studies of dietary salt restrictions to lower blood pressure have produced mixed results. Nevertheless, various clinical trials indicate some beneficial effects of dietary restriction of sodium on blood pressure, and it may also decrease the incidence of stroke and ischemic heart disease.

High consumption of potassium, found in foods like oranges, apricots, and dates, on the other hand, appears to have a protective action against cardiovascular diseases, although the mechanism of action is not known. Epidemiological studies have demonstrated an inverse relationship of potassium intake with blood pressure, incidence of stroke, and other cardiovascular diseases (Young, Huabao, and McCabe). A direct relationship between blood pressure and the ratio of sodium to potassium in the urine has also been found (Stamler).

Repeated intake over a long period of salt from salted and smoked products is associated with atrophic gastritis and gastric cancer. However, experimental evidence indicates that salt alone is not carcinogenic; the high dietary salt content may enhance the initiation of cancer by facilitating the action of any carcinogen, such as polycyclic aromatic hydrocarbons, present in the diet (Cohen and Roe, 1977), or potentiating Helicobacter pylori–associated carcinogenesis (Fox et al., 1999).

See also Minerals; Nutrient Requirements; Nutrition; Salt; Sodium; Thirst.

BIBLIOGRAPHY

Cohen, A. J., and F. J. Roe. "Evaluation of the Aetiological Role of Dietary Salt Exposure in Gastric and Other Cancers in Humans." Food and Chemical Toxicology 35 (1997): 271–293.

Fox, James G., et al. "High Salt Diet Induces Gastric Epithelial Hyperplasia and Parietal Cell Loss, and Enhances Helicobacter pylori Colonization in C57BL/6 Mice." Cancer Research 59 (1999): 4823–4828.

Lentner, Cornelius, ed. Geigy Scientific Tables. 8th ed., vol. 1. Basel: Ciba-Geigy Limited, 1981.

National Research Council. Recommended Dietary Allowances. 10th ed. Washington, D. C.: National Academy Press, 1989.

Palmer, Biff F., Robert J. Alpern, and Donald W. Seldin. "Physiology and Pathophysiology of Sodium Retention." In The Kidney: Physiology and Pathophysiology, edited by Donald W. Seldin and Gerhard Giebisch. 3d ed., Philadelphia: Lippincott Williams and Wilkins, 2000. Vol II, Chapter 54, pp. 1473–1517.

Rodriguez-Soriano, Juan. "Potassium Homeostasis and Its Disturbance in Children." Pediatric Nephrology 9 (1995): 364–374.

Stamler, Jeremiah. "The INTERSALT Study: Background, Methods, Findings, and Implications." American Journal of Clinical Nutrition 65 (1997): 626S–642S.

Toto, Robert D., and Donald W. Seldin. "Salt Wastage." In The Kidney: Physiology and Pathophysiology, edited by Donald W. Seldin and Gerhard Giebisch. vol. 2, 3d ed., pp. 1519–1536. Philadelphia: Lippincott Williams and Wilkins, 2000.

Young, David B., Huabao Lin, and Richard D. McCabe. "Potassium's Cardiovascular Protective Mechanisms." American Journal of Physiology 268 (1995): R825–R837.

Hwai-Ping Sheng

Diarrhea

Daily, about 8 to 10 l of water and large amounts of ions enter the gastrointestinal tract; about 1 to 2 l are from the diet, the rest from secretions of the alimentary tract. The greater part of this fluid is absorbed by the intestinal cells so that only about 150 ml of fluid are lost daily in the stool of an adult. Stools contain a low content of sodium and chloride but a high content of potassium so that the daily losses averages 6 mmol for sodium, 12 mmol for potassium, 3 mmol for chloride, and 5 mmol for bicarbonate. Loss of this water and ions can increase greatly in diarrhea, and if extreme, several liters of fluid can be lost, leading to dehydration and electrolyte and acid-base disturbances.

Diarrhea is defined as an increase in stool liquidity and a fecal volume of more than 200 ml/day in adults. Clinically, the most common and important causes of diarrhea are osmotic and secretory. Ingestion of a poorly absorbable solute, such as magnesium sulfate, or malabsorption or maldigestion of a specific solute because of enzyme deficiencies, as seen in lactase deficiency, can cause osmotic diarrhea. The presence of these solutes increases the intestinal luminal osmolarity, causing water to be retained in the lumen.

Various viral and bacterial infections can cause secretory diarrhea. Enteroinvasive bacteria such as Shigella and Salmonella invade intestinal mucosa to produce ulceroinflammatory lesions resulting in a failure of normal absorption. On the other hand, bacteria such as Vibrio cholerae release toxins that increase secretion of sodium chloride and water. If the cholera is severe, up to 18 l of watery stools can be passed in a day. These stools contain ionic concentrations similar to that of plasma, so that large amounts of sodium, chloride, and potassium can be lost.

Dehydration caused by diarrhea ranges from mild to severe. The severity of dehydration can be assessed clinically by examining the patient for sunken eyeballs, skin turgor, mental status, blood pressure, and urine output. Fluid replacement is of utmost importance, especially in severe dehydration, to prevent circulatory collapse. Although diarrhea causes losses of sodium as well as potassium and bicarbonate, the immediate concern in treating severe diarrhea is to replace sodium and water to restore the circulatory volume. Dehydration in diarrhea can be reversed by oral or, in emergency, intravenous rehydration therapy.

The World Health Organization has recommended the use of oral rehydration therapy for treatment of mild to moderate cases of diarrhea. This program has been very successful in reducing mortality from diarrheal diseases, particularly in infants in developing countries. Oral rehydration fluid contains 3.5 g of sodium chloride, 2.5 g of sodium bicarbonate, 1.5 g of potassium chloride, and 20 g of glucose in 1 l of water. An alternative household remedy is to make a solution containing three "finger pinches" of salt, a "fistful of sugar" and one quart of water. Addition of sugar to the oral rehydration fluid helps to increase the absorption of sodium chloride through the sodium-glucose transporter system in the small intestine.

Thermoregulation Through Perspiration

Heat is produced continuously by the body during metabolism, and it is also taken up by the body from the environment by radiation and conduction. Heat is lost from the body by radiation, conduction and convection, and evaporation. Even in the absence of perspiration, water is lost continuously from the body by evaporation from the upper respiratory tract and by passive evaporation from the skin. These insensible water losses amount to a total of about 0.6 l/day, of which slightly more than 50 percent is from the skin. For every liter of water that evaporates from the body, 580 kcal (2428 kJ) of heat is dissipated. During intense physical exertion or at a high ambient temperature, loss of heat from radiation, conduction, and insensible water loss are insufficient to prevent a rise in body temperature. Under these circumstances, heat loss is enhanced by the production and evaporation of sweat. Loss of heat by evaporation of sweat is an effective means of removing excess heat from the body, and it can be controlled by regulating the rate of sweating. When the body temperature rises above 98.6°F (37°C), stimulation of the temperature-regulating center in the hypothalamus causes sweating.

Sweat is produced by sweat glands by actively secreting into ducts a fluid similar in composition to that of plasma. As this primary secretion passes along the ducts of the sweat glands to the surface of the skin, sodium and chloride are absorbed in excess of water, resulting in the production of a dilute fluid that has a lower content of sodium and chloride. Sodium chloride content in sweat varies; it depends on the rate of flow. For a young adult, the average value is about 50 mmol/l for sodium and 30 mmol/l for chloride. The transport mechanisms for sodium and chloride are affected in patients suffering from cystic fibrosis so that their concentrations in the sweat are increased. For the purpose of diagnosis, the upper limit of the normal values for children and young adults are set at 70–80 mmol/l for sodium and 60–70 mmol/l for chloride (Lentner, ed.).

Rate of sweat production depends on the ambient temperature and humidity, and the degree of activity of the individual. For a 70 kg man doing light work at an ambient temperature of 84°F (29°C), daily loss is about 2 to 3 l. An unacclimatized individual who is performing hard physical activity in a hot, humid environment may lose, for a short time, up to 2 to 4 l/hour of sweat. As the duration of perspiration increases, the rate of production decreases to about 0.5 l/hour. Therefore, even at maximal sweating, the rate of heat loss may not be rapid enough to dissipate the excess heat from the body. Dehydration from excessive loss of water and sodium chloride stimulates the thirst mechanism, and if water intake is not increased, it can cause weakness and, if severe, circulatory collapse.

Adaptation to heat leads to physiological changes that include an increase in sweat production, an increase in plasma volume, and a decrease in concentration of sodium and chloride in the sweat and urine. These latter two effects are caused by an increase in aldosterone secretion as a result of dehydration and loss of sodium from the body. The decrease in the concentration of sodium and chloride in sweat and urine allows for better conservation of these ions in the body. An unacclimatized person who sweats profusely often loses as much as 13 to 30 g of salt per day for the first few days, but after four to six weeks of acclimatization the loss can be as low as 3 to 5 g a day.

There is a limit at which the body can lose heat even when perspiring maximally. The progressive rise in body temperature will affect the heat-regulating ability of the hypothalamus, resulting in a decrease in sweating. Therefore, a high body temperature tends to perpetuate itself unless measures are taken specifically to decrease the body temperature. When the body temperature rises beyond a critical temperature of 106°F (41°C), the person is likely to develop heat stroke. Symptoms include dizziness, abdominal distress, delirium, and eventually loss of consciousness. Some of these symptoms are exacerbated by a mild degree of circulatory shock as a result of sodium loss and dehydration.

Electrolytes

Definition

Purpose

Description

Precautions

Interactions

Complications

Parental concerns

Resources

Definition

Electrolytes are ions that form when salts dissolve in water or fluids. These ions have an electric charge. Positively charged ions are called cations. Negatively charged ions are called anions. Electrolytes are not evenly distributed within the body, and their uneven distribution allows many important metabolic reactions to occur. Sodium (Na⁺ ), Potassium (K⁺ ), Calcium (Ca2+), Magnesium (Mg2+ ), chloride (Cl-), phosphate (HPO42-), bicarbonate (HCO3-), and Sulfate (SO4-) are important electrolytes in humans.

Purpose

Electrolytes play a critical role in almost every metabolic reaction in the body. For example, they:

• Help control water balance and fluid distribution in the body
• Create an electrical gradient across cell membranes that is necessary for muscle contraction and nerve transmission

KEY TERMS

Diuretic —A substance that removes water from the body by increasing urine production

Glucose —A simple sugar that results from the breakdown of carbohydrates. Glucose circulates in the blood and is the main source of energy for the body

Homeostasis —The complex set of regulatory mechanisms that works to keep the body at optimal physiological and chemical stability in order for cellular reactions to occur

Hormone —A chemical messenger produced by one type of cell and travels through the bloodstream to change the metabolism of a different type of cell

Serum —The clear fluid part of the blood that remains after clotting. Serum contains no blood cells or clotting proteins, but does contain electrolytes.

• Regulate the acidity (pH) of the blood
• Help regulate the level of oxygen in the blood
• Are involved in moving nutrients into cells and waste products out of cells

Description

Water is essential to life. Dehydration occurs when more water is lost from the body than is replaced. A loss of 20% of the body’s water can be fatal. Water balance and electrolyte concentrations are closely intertwined. Dehydration is a major cause of electrolyte imbalances

Electrolytes, proteins, nutrients, waste products, and gasses are dissolved in fluid in the body. This fluid is not distributed evenly. About two-thirds of it is found inside cells (intracellular fluid). The rest is found in the spaces between cells (interstitial fluid), in the circulatory system, and in small amounts in other places such as the stomach. Changes in the concentration of electrolytes results in changes to the distribution of water throughout the body as water moves into or out of cells

The components of body fluid—electrolytes, proteins, and so forth—are not evenly distributed either. Different types of cells have membranes that allow some electrolytes (and other components of the fluid) to pass across them while blocking others. This difference in the distribution of electrolytes (and thus electric charges) on either side of cell membranes makes it possible for many metabolic reactions to take place

Water passes easily across cell membranes. When fluid with two different concentrations of electrolytes is separated by a cell membrane, there is pressure (called osmotic pressure) for water to flow across the membrane from fluid that contains fewer electrolytes (less concentrated) into fluid that contains more electrolytes (more concentrated). The cell uses energy to resist osmotic pressure and maintain different concentrations of electrolytes on either side of the membrane because even small changes in the concentrations and distribution of electrolytes can result in large movements of water in and out of cells. Maintaining this difference, or gradient, across cell membranes is a major part of the complex regulatory events called homeostasis that keep conditions within the body stable within very narrow limits. When there is an imbalance in electrolytes many systems in the body are affected and serious, even fatal, health problems can result.

Causes of electrolyte imbalances

An electrolyte imbalance occurs when the concentration of a specific electrolyte is either too high or too low. The concentration of electrolytes is strongly affected by the amount of fluid in the body. Fluid balance is largely controlled by hormones that act on the kidneys and regulate how much urine the kidneys produce. The average male adult loses about 1.5-2.5 L of water daily through urine production, sweating, breathing out water vapor, and bowel movements depending on exercise levels and environmental temperature. The United States Institute of Medicine recommends that adult men drink a minimum of 3 L of liquids a day, and that women drink a minimum of 2.2 L to replace lost water

Dehydration is a major cause of electrolyte imbalance. It occurs whenever water is lost from the body and not replaced fairly quickly. When fluids are lost, electrolytes in those fluids are lost too, increasing the risk of electrolyte imbalance. Dehydration can be caused in many ways. These include:

• Heavy exercise, especially in hot weather. Sodium and water are both lost through the skin with heavy sweating
• Limited fluid intake. This is a particular problem with the elderly, especially those who are unable to walk or are bedridden
• Severe vomiting and diarrhea. Large amounts of water and many electrolytes that would normally be absorbed in the intestines are lost with diarrhea and vomiting. Small children with diarrhea can become seriously dehydrated in less than one day. Infants can become dehydrated within hours
• High fever. Increased water loss through the skin due to fever is especially serious in infants and young children
• Severe burns. More water is lost from the surface of the body when the skin is not there to prevent evaporation, and damaged cells release their electrolytes into interstitial fluid, upsetting the electrolyte balance

Electrolyte imbalances can have other causes unrelated to dehydration. These include:

• Kidney damage or kidney failure. This is a common cause of electrolyte imbalances in the elderly and can be fatal
• Anorexia nervosa (self starvation) or bulimia nervosa (binge and purge eating)
• Excessive intake of water. Called water intoxication, this can result in swelling in the brain. In 2007, a Sacramento, California, woman died when she participated in a radio station contest that involved drinking large amounts of water in a short period of time
• Some drugs, herbal supplements, and chemotherapy. Some medications/treatments selectively increase the excretion of certain electrolytes, cause the body to retain excess water, or stimulate the kidneys to produce excess urine
• Hormonal imbalances in the production of hormones that regulate the kidneys. This causes too little or too much urine to be produced
• Cancer. Some tumors produce chemicals that upset electrolyte balance
• Abuse of electrolyte supplements

Specific electrolyte imbalances

Each electrolyte has a special function in the body, although if one electrolyte is out of balance, the concentrations and actions of other electrolytes are often affected. The serum concentration of sodium, potassium, and chloride can be measured in a simple blood test. Sodium, chloride, potassium, and calcium concentrations can also be determined from a urine sample. A urine test helps show how well the kidneys are functioning. Electrolyte imbalances are most common among the seriously ill and the elderly. Kidney (renal) failure is the most common cause of electrolyte imbalances

SODIUM . Sodium affects how much urine the kidney produces and is involved in the transmission of nerve impulses and muscle contraction. Too high a concentration of sodium in the blood causes a condition called hypernatremia. Causes of hypernatremia include excessive water loss (e.g., severe diarrhea), restricted water intake, untreated diabetes (causes water loss), kidney disease, hormonal imbalances, and excessive salt (NaCL) intake. Symptoms include signs of dehydration such as extreme thirst, dark urine, sunken eyes, fatigue, irregular heart beat, muscle twitching, seizures, and coma

Too low a concentration of sodium in the blood causes hyponatremia. This is one of the most common electrolyte imbalances, and occurs in about 1% of hospitalized individuals. It can result from vomiting, diarrhea, severe burns, taking certain drugs that cause the kidneys to selectively excrete sodium, inadequate salt intake, water intoxication (a problem among the elderly with dementia), hormonal imbalances, kidney failure, and liver damage. Symptoms include nausea, vomiting, headache, tissue swelling (edema), confusion, mental disorientation, hallucinations, muscle trembling, seizures, and coma

POTASSIUM . Potassium ions play a major role in regulating fluid balance in cells, the transmission of nerve impulses, and in muscle contractions. Too high a concentration of potassium causes a condition called hyperkalemia that is potentially life threatening. The most common cause is kidney failure. It can also result from severe burns or injury (excess potassium released from injured cells), inadequate adrenal hormones (Addison’s disease), the use of certain medications, and excessive use of potassium supplements. Sometimes hyperkalemia occurs in conjunctions with hypernatremia. Symptoms include nausea, diarrhea, weakness, muscle pain, and irregular heart beat, coma and death

Abnormally low concentrations of potassium cause hypokalemia. Hypokalemia can result from excess adrenal hormones (Cushing’s disease), kidney disease, long-term use of certain diuretic drugs, laxative abuse, bulimia, and kidney failure. Symptoms include increased production of urine, muscle pain, paralysis, irregular heart beat, and low blood pressure

CALCIUM . Calcium is needed to build and maintain bones. It also plays a role in nerve impulse transmission and muscle contraction. Excess calcium results in a condition called hypercalcemia. Hypercal-cemia can be caused by too much parathyroid hormone (PTH), certain cancers, some genetic disorders, and excessive use of antacids containing calcium in rare cases. Symptoms include bone and muscle pain, mental changes such as depression and confusion, increased urine production, fatigue, nausea, and vomiting

Abnormally low concentrations of calcium cause hypocalcemia. Hypocalcemia can be caused by too little parathyroid hormone, kidney failure, and vitamin D deficiency . Vitamin D is necessary for the body to absorb calcium. Symptoms include muscle twitches and spasms, convulsions, mental changes such as depression and irritability, dry skin, and brittle nails

MAGNESIUM . Magnesium is involved in protein synthesis and cellular metabolism . Abnormally high concentrations of magnesium, or hypermagnesemia, may occur with severe (end-stage) renal failure or by overdose of magnesium-containing intravenous fluids. Hypermagnesemia is rare. Symptoms include exhaustion, low blood pressure, depressed heart and breathing rate, and slow reflexes

Abnormally low concentrations of magnesium, or hypomagnesemia, are most common among people with alcoholism and those who are severely malnourished. Other causes include digestive disorders that interfere with the absorption of magnesium from the intestines. Symptoms of hypomagnesemia include vomiting, weight lose, leg cramps, muscle spasms, seizures, and irregular heartbeat

CHLORIDE . Chloride is involved in regulating blood pressure. High concentrations of chloride, called hyperchloremia, can be caused by kidney failure, kidney dialysis, and an overproduction of parathyroid hormone. Symptoms include weakness, headache, nausea, and vomiting. In people with diabetes, hyperchloremia makes it difficult to control blood glucose levels

Hypochloremia often occurs along with hypona-tremia or hypokalemia and is caused by excessive fluid loss (e.g., diarrhea). Serious deficiencies of chloride cause the blood to become less acidic, resulting in a condition called metabolic alkalosis. Symptoms of severe hypochloremia include confusion, paralysis, and difficulty breathing

PHOSPHATE . Phosphate helps control the acidity level (pH) of the blood. Phosphate also causes calcium to be deposited in bones. High blood levels of phosphate, or hyperphosphatemia, often result in too low levels of calcium, or hypocalcemia. Hyperphosphatemia is usually caused by kidney failure. It can also result from kidney dialysis, parathyroid gland dysfunction, and several inherited diseases. Mild hyperphosphatemia usually produces no symptoms. Severe imbalance can cause tingling in the fingers, muscle cramps, and convulsions

Hypophosphatemia, or abnormally low concentrations of phosphate in the blood, often occurs along with hypomagnesemia and hypokalemia. It can also be caused by kidney disease, kidney dialysis, vitamin D deficiency, and hormonal imbalances. Up to 30% of individuals admitted to hospital intensive care units have hypophosphatemia.

Electrolyte supplements

Most people get all the electrolytes and water they need from a normal diet. However, some individuals, such as athletes, people with severe diarrhea and vomiting, cancer patients, people with hormonal imbalances, and other very ill people, need fluid and electrolyte replacement therapy. Short-term therapy often quickly restores electrolyte balances

Electrolyte replacement supplements can be sold either over-the-counter or by prescription. Prescription supplements are used for seriously ill or hospitalized patients and can be given by mouth or intravenously under supervision of a physician

In North America, commonly used over-the-counter electrolyte replacements include:

• Sports drinks formulated to replace electrolytes lost through sweating. These drinks, such as Gatorade and Powerade, also contain sugars and sometimes caffeine. According to the American College of Sports Medicine, sports drinks are effective in supplying energy for muscles, maintaining blood sugar levels, preventing dehydration, and replacing electrolytes lost in sweat
• Dietary supplements in the form of tablets and powders containing electrolytes. These are popular among athletes who participate in endurance sports. Some also contain herbs and flavorings. They are regulated by the United States Food and Drug Administration (FDA) as dietary supplements
• Electrolyte replacements for children such as Pedialyte, Naturalyte, or Rehydralyte. These are sold in supermarkets and pharmacies and are used primarily in children who have lost fluids through vomiting and diarrhea. Children should not be given sports drinks for this purpose

Precautions

As with any dietary supplement, electrolyte replacements can be abused. When used properly, they are of great benefit and have no undesirable side effects

Sports drinks should not be given to children who need rehydration because of vomiting and diarrhea. Instead, oral rehydration liquids specially formulated for children should be used

Interactions

The goal of electrolyte replacement therapy is to restore the body to its natural condition. When used this way, electrolyte replacement does not interfere with other drugs. Many drugs, however, have the potential to cause electrolyte imbalances. When starting a new drug, individuals should discuss possible side effects with their healthcare provider.

Complications

No complications are expected when electrolyte replacement therapy is used as directed. Seriously ill individuals and those using long-term electrolyte replacement therapy should have their electrolyte levels checked regularly.

Parental concerns

Dehydration is a real threat to children, especially infants and toddlers. Parents should be alert to dehydration caused by illness or athletic activity and begin oral fluid and electrolyte replacement therapy immediately. Parents of young children with vomiting, diarrhea, or high fever should consult their healthcare provider promptly about steps to take to prevent dehydration.

Resources

BOOKS

Hawkins, w. Rex. Eat Right—Electrolyte: A Nutritional Guide to Minerals in Our Daily Diet. Amherst, NY: Prometheus Books, 2006.

ORGANIZATIONS

American Academy of Pediatrics. 141 Northwest Point Blvd. Elk Grove Village, IL 60007. Telephone: (847) 434-4000. Website: http://www.aap.org>

American College of Sports Medicine. 401 West Michigan Street, Indianapolis, IN 46202. Telephone: (317) 637-9200. Fax: (317) 634-7871. Website: http://www.acsm.org>

OTHER

“Electrolytes.” Lab Tests Online. April 11, 2005. [cited May 6, 2007]. http://www.labtestsonline.org/understanding/analytes/electrolytes/glance.html>

Kenney, Larry. “Dietary Water and Sodium Requirements for Active Adults.” Sports Science Exchange 92.17, no.1 (2004). [cited May 6, 2007]. http://www.gssiweb.com/Article_Detail.aspx?articleID=667>

Micromedex. “Carbohydrates and Electrolytes (System-ic).”MayoClinic.com May 21, 1998. [cited May 6, 2007]. http://www.mayoclinic.com/health/drug-information/DR202112>

Murray, Robert. “The Risk and Reality of Hyponatremia.” Gatorade Sports Science Institute. [cited May 6, 2007]. http://www.gssiweb.com/>

Helen Davidson.

electrolytes Chemically salts that dissociate in solution and will carry an electric current; clinically used to mean the mineral salts of blood plasma and other body fluids, especially sodium and potassium.