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Electrolytes

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
  • 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.

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.


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