dehydration

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1. Removal of water from a substance. 2. A chemical reaction in which a compound loses hydrogen and oxygen in the ratio 2:1. For instance, ethanol passed over hot pumice undergoes dehydration to ethene:

Substances such as concentrated sulphuric acid, which can remove H₂O in this way, are known as dehydrating agents. For example, with sulphuric acid, methanoic acid gives carbon monoxide:

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Food

Medicine

For more information on dehydration, visit Britannica.com.

Drying, normally used for factory-dried, as distinct from wind-dried, materials.

Dehydration (loss of fluids from the body) is a hazard in many sports and can be a serious medical problem. It is also a problem associated with some weight loss techniques, such as steam baths, plastic sweat suits, and diuretic pills (water tablets). Dehydration can result in overheating, a potentially dangerous lowering of blood pressure, and a reduction in the rate at which blood is pumped out of the heart. These effects can lead to illness, heat stroke, and even death. Dehydration can occur during exercise when the amount of fluid lost through sweating is greater than fluid replacement through drinking. It can cause poor performances even in temperate climates. A 2 per cent loss of body weight due to water loss, can lead to a 20 per cent drop in the working capacity of muscles. Dehydration reduces both the speed and strength of muscular contractions. To minimize the risk, water should be freely available during exercise and competitive sports. See also heat stroke and water replacement.

Definition

Dehydration is the loss of water and salts that are essential for normal body function.

Description

Dehydration occurs when the body loses more fluid than it takes in. Dehydration can upset the delicate fluid-salt balance needed to maintain healthy cells and tissues. The human body is generally over 60 percent water. The body works to maintain water balance through mechanisms such as the thirst sensation. When the body requires more water, the brain stimulates nerve centers to encourage a person to drink in order to replenish the water stores. Water intake can vary widely on a daily basis, influenced by such factors as access to water, thirst, habit, and cultural factors.

The kidneys are responsible for maintaining water balance through the elimination of waste products and excess water. Water is primarily absorbed through the gastrointestinal tract and excreted by the kidneys as urine. The variation in water volume ingested is dependent on the ability of kidneys to dilute and concentrate the urine as needed.

Children need more water than adults because they expend more energy, and most children who drink when they are thirsty get as much water as their systems require. Dehydration in children usually results from losing large amounts of fluid and not drinking enough water to replace the loss. This condition generally occurs in children who have a stomach flu characterized by vomiting and diarrhea or who cannot or will not take enough fluids to compensate for excessive losses associated with fever and sweating of acute illness. Dehydration can result from illness; a hot, dry climate; prolonged exposure to sun or high temperatures; not drinking enough water; and overuse of diuretics or other medications that increase urination.

Types of Dehydration

Dehydration is classified as mild, moderate, or severe based on how much of the body fluid is lost, estimated by loss in bodyweight. Mild dehydration is the loss of no more than 5 to 6 percent loss of body weight. Loss of 7 to 10 percent is considered moderate dehydration. Severe dehydration (loss of over 10 percent of body weight) is a life-threatening condition that requires immediate medical care.

Complications of Dehydration

When the body's fluid supply is severely depleted, hypovolemic shock is likely to occur. This condition, which is also called physical collapse, is characterized by pale, cool, clammy skin; rapid heartbeat; and shallow breathing.

Blood pressure sometimes drops so low it cannot be measured, and skin at the knees and elbows may become blotchy. Anxiety, restlessness, and thirst increase. After a child's temperature reaches 107°F (41.7°C) damage to the brain and other vital organs occurs quickly.

Demographics

Dehydration is a major cause of infant illness and death throughout the world. Dehydration is often a result of gastrointestinal disease and diarrhea in children. Among children in the United States, short-term diarrhea results in approximately 200,000 hospitalizations and 300 deaths per year. In developing countries, dehydration from illness is a common cause of death in children under five years of age, accounting for about 2 million deaths per year.

Causes and Symptoms

Dehydration is a deficit of body water that results when the output of water exceeds intake. Dehydration stimulates a child's thirst mechanism. Causes of dehydration may include the following:

• decreased water or fluid intake
• diarrhea
• vomiting
• excessive heat
• excessive sweating
• fever
• excessive urination (polyuria)
• diuretics or other medication that increase fluid loss
• caffeine or alcohol consumption

Sweating and the output of urine both decrease during dehydration. If water intake continues to fall short of water loss, dehydration worsens and a child may become critically ill.

Reduced fluid intake may be a result of the following:

• appetite loss associated with acute illness
• nausea
• bacterial or viral infection or inflammation of the pharynx (pharyngitis)
• inflammation of the mouth caused by illness, infection, irritation, canker sores, or vitamin deficiency

Other conditions that can lead to dehydration include the following:

• disease of the adrenal glands, which regulate the body's water and salt balance and the function of many organ systems
• diabetes mellitus
• eating disorders
• kidney disease
• chronic lung disease

With mild dehydration, increased thirst and restlessness are usually the only apparent symptoms. In moderately dehydrated children, eyes are somewhat sunken, and the mouth and tongue are dry. Thirst is increased: an older child asks for water, and a younger child drinks eagerly when offered a cup or spoon of water. The skin is less elastic than it should be and is slow to return to its normal position after being pinched. The radial pulse (wrist area) is detectable, but rapid. The soft spot on a baby's head (fontanelle) is somewhat sunken. Two of the following symptoms usually indicate some degree of dehydration: drinks eagerly, thirsty, restless, irritable, sunken eyes, or skin pinch goes back slowly.

Children with severe dehydration are usually lethargic, in a stupor, or even in a coma. Symptoms are even more apparent (deeply sunken eyes without tears, very dry mouth and tongue, rapid and deep breathing). A skin pinch retracts very slowly (over two seconds). Children who are awake are very thirsty, although a child may drink poorly if in a stupor. A child may not have urinated for six hours or longer. When in hypovolemic shock, systolic blood pressure taken in the arm is low or not detectable, the arms and legs are cool, and the nail beds may have a bluish or purplish discoloration. Two of the following symptoms indicate severe dehydration: lethargic or unconscious, very slow skin pinch, sunken eyes, and not able to drink or drinking poorly.

Dehydration can cause confusion, constipation, discomfort, drowsiness, and fever. The skin turns pale and cold, the mucous membranes lining the mouth and nose lose their natural moisture. The pulse sometimes races and breathing becomes rapid. Significant fluid loss can cause serious neurological problems or death.

When to Call the Doctor

A doctor should be notified whenever an infant or child exhibits signs of dehydration or a parent is concerned that a stomach virus or other acute illness may lead to dehydration.

A doctor should also be notified if any of the following is the case:

• Symptoms of dehydration worsen.
• A breast-fed or bottle-fed infant is unable to feed or feeds poorly.
• An infant or child urinates very sparingly or does not urinate at all during a eight-hour period.
• An infant younger than two months of age has diarrhea or is vomiting.
• Dizziness, listlessness, or excessive thirst occurs.
• The child's heart is beating fast.
• The child has dry eyes, sunken eyes, a dry mouth, or is not producing tears.
• There is blood in the stool or vomit.

An infant can become dehydrated within hours after the onset of illness. In general, the smaller the child, the lower the threshold should be for healthcare intervention if dehydration is suspected.

Diagnosis

A child's symptoms and medical history alone usually suggest dehydration. Physical symptoms are usually all that is necessary for diagnosing dehydration, although laboratory tests may be ordered by the physician. Physical examination may reveal shock, rapid heart rate, and/or low blood pressure. Laboratory tests, including blood tests (to check electrolyte levels) and urine tests (e.g. urine specific gravity and creatinine), may be used to evaluate the severity of the problem.

Treatment

Increased fluid intake and replacement of lost electrolytes are extremely important for restoring fluid balances in infants and children who are dehydrated. Treatment is given based on severity of dehydration. Treatment should include two phases: a rehydration phase and a maintenance phase. In the rehydration phase, fluid losses are replaced quickly, within three to four hours until normal hydration is achieved. In the maintenance phase, calories and fluids are given. Rapid refeeding should follow rapid rehydration with the goal of returning the child to an unrestricted, age-appropriate diet including solids. Withholding foods to rest the gut is not recommended. Breastfeeding should be continued at all times through both stages of treatment. Full-strength formula is usually tolerated. Changing formula or diluting to half strength are common practices but are usually unnecessary and may even prolong symptoms and delay nutritional recovery.

To replace calories quickly during acute illness, food should be given as soon as the child will tolerate it. During both rehydration and maintenance phases, fluid losses from vomiting and diarrhea should be replaced continuously. Restricting lactose (milk and milk products) is usually not necessary but may be helpful in a child with a severe intestinal disease or diarrhea in a malnourished child.

Children with minimal dehydration weighing less than 10 kilograms (22 pounds) should be given 60 to 120 mL (2–4 ounces) of an oral rehydration solution (ORS) for each episode of vomiting or diarrheal stool. Those weighing more than 10 kg (22 lbs) should be given 120 to 240 mL (4–8 ounces). Food should not be restricted. Children with mild to moderate dehydration should be given 50 to 100 mL (roughly 2–3.5 ounces) of an ORS per kilogram body weight during two to four hours to replace fluid losses. Additional ORS should be administered to replace ongoing losses from vomiting and diarrhea. In a sick child, a teaspoon, syringe, or medicine dropper can be used to offer a small amount at first with amounts increasing as tolerated. If the child appears to want more, more can be given. Severe dehydration is a medical emergency requiring intravenous fluids immediately.

For moderate or severe dehydration, a child should be treated in a medical facility. Moderate dehydration can be treated orally, but severe dehydration requires the child to take fluids intravenously (IV). When treating dehydration, the underlying cause must also be addressed. For example, if dehydration is caused by vomiting, medications may be prescribed to resolve these symptoms. However, anti-diarrheal medications are not recommended in children. A child who is dehydrated due to diabetes, kidney disease, or adrenal gland disorders must receive treatment for these conditions as well as for the resulting dehydration.

For older children who are mildly dehydrated, just drinking plain water may be all the treatment that is needed. For infants and younger children, especially when ill, drinking a commercial ORS should be encouraged. Parents should follow label instructions when giving children Pedialyte or other commercial products recommended for relieving dehydration. Sports drinks are not recommended as they contain a lot of sugar and may worsen diarrhea.

In order to accurately calculate fluid loss, it is important to chart weight changes every day and keep a record of how many times a child vomits or has diarrhea. Parents should note how many times a baby's diaper must be changed.

Alternative Treatment

Gelatin water may be substituted for electrolyte-replacement solutions if an ORS is unavailable. It is made by diluting a 3-oz package in a quart of water or by adding one-fourth teaspoon of salt and a tablespoon of sugar to a pint of water. Receiving the right amount of electrolytes is very important, and thus homemade remedies such as gelatin (or adding salt or sugar to water) are not recommended because of the potential for quantity errors when mixing. However, these may be useful if ORS cannot be obtained in an emergency. Parents should keep a can of ORS on hand for emergencies.

Formulas containing soy fiber have been reported to reduce liquid stools.

Prognosis

Mild dehydration rarely results in complications. If the cause is eliminated and lost fluid is replaced, mild dehydration can usually be cured quickly.

Vomiting and diarrhea that continue for several days without adequate fluid replacement can be fatal. However, dehydration that is rapidly recognized and treated has a good outcome.

Prevention

Ensuring that children always drink adequate fluids during an illness helps to prevent dehydration. Parents can prevent dehydration in infants and children who are vomiting or who have diarrhea by increasing fluids to compensate for losses. Infants and children with diarrhea and vomiting should be given ORS such as Pedialyte immediately to help prevent dehydration.

Children who are not ill can maintain proper fluid balance by drinking water or fluids even before they are thirsty. Children should drink fluids before going outside to exercise or play (especially on a hot day). Dehydration can usually be prevented by drinking enough fluid for urine to remain the color of pale straw. Water in foods, especially fruits and vegetables, is a great source of fluid. Fruits and vegetables can contain up to 95 percent water, so a well-balanced diet is a good way to stay hydrated.

Parents should know whether any medication their child is taking can cause dehydration and should get prompt medical care to correct any underlying condition that increases the risk of dehydration.

Other methods of preventing dehydration and ensuring adequate fluid intake are as follows:

• eating more soup at mealtime
• drinking plenty of water and juice at mealtime and between meals
• keeping a glass of water nearby

Children should not be given coffee or tea, because they increase body temperature and water loss. Avoiding caffeinated soft drinks may also reduce the risk of dehydration. These beverages are all diuretics (substances that increase fluid loss).

Resources

Books

Batmanghelidj, F. Water: For Health, For Healing, For Life: You're Not Sick, You're Thirsty! New York: Warner Books, 2003.

Kleinman, Ronald E., and the American Academy of Pediatrics Committee on Nutrition. Pediatric Nutrition Handbook, 5th ed. Elk Grove Village, IL: American Academy of Pediatrics, 2003.

Physicians Committee for Responsible Medicine. Healthy Eating for Life for Children. Hoboken, NJ: Wiley, 2002.

Speakman, Elizabeth, and Norma Jean Weldy. Body Fluids and Electrolytes, 8th ed. London: Mosby Incorporated, 2001.

Willett, Walter C., and P. J. Skerrett. Eat, Drink, and Be Healthy: The Harvard Medical School Guide to Healthy Eating. New York: Simon & Schuster Source, 2002.

Workman, M. Linda. Introduction to Fluids, Electrolytes and Acid-Base Balance. London: Saunders, 2001.

Periodicals

Steiner, M. J., et al. "Is this child dehydrated?" Journal of the American Medical Association 291, no. 22 (June 2004): 2746–54.

Organizations

American Academy of Pediatrics. 141 Northwest Point Blvd., Elk Grove Village, IL 60007–1098. Web site: www.aap.org.

American College of Emergency Physicians. 1125 Executive Circle, Irving, TX 75038–2522. Web site: www.acep.org.

Web Sites

Rehydration Project. Available online at www.rehydrate.org (accessed November 16, 2004).

"Why Is Dehydration so Dangerous?" Rehydration Project. Available online at www.rehydrate.org/dehydration/index.html (accessed November 16, 2004).

[Article by: Crystal Heather Kaczkowski, MSc. Maureen Haggerty]

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The removal of water vapor from air by the use of absorbing or adsorbing materials.

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A depletion of fluids from the body that can hinder thermoregulation and cause an increase in core temperature. A reduction of the body's fluid volume may result in a lowering of blood pressure and cardiac output. Dehydration occurs during exercise if the fluid lost through perspiration and urine exceeds fluid replacement. Mild dehydration may cause a general malaise and insomnia, and it leads to poor performances even in temperate climates. A two% loss of body-weight due to water loss can lead to a 20% drop in the working capacity of muscles. Training may increase tolerance to dehydration. See also heat stroke, water replacement.

Dehydration is the excessive loss of water from the body. Water can be lost through urine, sweat, feces, respiration, and through the skin. Symptoms of dehydration in order of severity are: thirst, nausea, chills, clammy skin, increased heart rate, muscle pain, reduced sweating, dizziness, headache, shortness of breath, dry mouth, fatigue, lack of sweating, hallucinations, fainting, and loss of consciousness. Dehydration can affect mental alertness, renal function, circulation, and total physical capacity.

The following can help to avoid dehydration:

1. Drink before feeling thirsty
2. Drink enough fluid to have pale yellow urine
3. Avoid caffeine and alcohol, which act as diuretics
4. Drink two to three cups of fluid two hours before exercise or heavy outside work in hot temperatures
5. Drink one to two cups of fluid every fifteen minutes during exercise or heavy outside work in hot temperatures
6. Avoid exercising during midday heat, and wear appropriate clothing that allows airflow around the body

Athletes, elderly persons, young children, and those with specific illnesses that affect fluid balance, such as severe diarrhea, are at higher risk for dehydration than the average person.

See also Malnutrition; Oral rehydration therapy; Sports nutrition.

Bibliography
Dorland's Pocket Medical Dictionary, 23d edition (1982). Philadelphia: W. B. Saunders.
Berning, Jacqueline R., and Steen, Suzanne Nelson (1998). Nutrition for Sport and Exercise, 2nd edition. Gaithersburg, MD: Aspen.

KEY TERMS Diabetes—a condition in which the body either does not make or cannot respond to the hormone insulin. As a result, the body cannot use glucose (sugar). There are two types, type 1 and type 2. Diuretic—a substance that removes water from the body by increasing urine production. Electrolyte—ions in the body that participate in metabolic reactions. The major human electrolytes are sodium (Na+), potassium (K+), calcium (Ca 2+), magnesium (Mg2+), chloride (Cl-), phosphate (HPO 2-), bicarbonate (HCO-), and sulfate (SO 2-). Laxative—A substance that stimulates movement of food through the bowels. Laxatives are used to treat constipation.

    Demographics
    Causes and symptoms
    Diagnosis
    Treatment
    Nutrition concerns
    Prognosis
    Prevention
    Resources

What is Dehydration?

Dehydration is a condition in which the body looses too much water usually as a result of excess sweating, vomiting, and/or diarrhea.

Description of Dehydration

Dehydration occurs because more fluid is lost from the body than is taken in. Water is essential for life. Transporting nutrients throughout the body, removing wastes, regulating body temperature, lubrication of joints and membranes, and chemical reactions that occur during cellular metabolism all require water.

The amount of water a person needs to prevent dehydration varies widely depending on the individual’s age, weight, level of physical activity, and the environmental temperature. The individual’s health and the medications they take may also affect the amount of water a person needs. Most dehydration results from an acute, or sudden, loss of fluids. However, slow-developing chronic dehydration can occur, most often in the frail elderly and infants and young children who must rely on others to supply them with liquids.

Healthy people lose water from urination, elimination of solid wastes, sweating, and breathing out water vapor. This water must be replaced through diet. Water makes up about 75% of the body weight of infants, 65% of the weight of children and 60% of the weight of an adult. In 2004, the United States Institute of Medicine (IOM) recommended that relatively inactive adult men take in about 3.7 L (about 15 cups) of fluids daily and that women take in about of 2.7 liters (about 10 cups) to replace lost water. These recommendations are for total fluid intake from both beverages and food. Highly active adults and those living in very warm climates need more fluids.

About 80% of the water the average person needs is replaced by drinking liquids. The other 20% is found in food. Below are listed some foods and the percentage of water that they contain.

• iceberg lettuce 96%
• squash, cooked. 90%
• cantaloupe, raw, 90%
• 2% milk 89%
• apple, raw 86%
• cottage cheese 76%
• potato, baked 75%
• macaroni, cooked 66%
• turkey, roasted 62%
• steak, cooked 50%
• cheese, cheddar 37%
• bread, white 36%
• peanuts, dry roasted 2%

Dehydration involves more than just water deficiency. Electrolytesare ions that form when salts dissolve in water or body fluids. In order for cells to function correctly, the various electrolytes, such as sodium(Na+ ) and potassium (K+), must remain within a very narrow range of concentrations. Often electrolytes are lost along with water. For example sodium is lost in sweat. To prevent the effects of dehydration, both water and electrolytes must be replaced in the correct proportions.

Signs of dehydration

General dehydration

• Thirst
• Less frequent urination
• Dry skin
• Fatigue
• Light-headedness
• Dark colored urine

Dehydration in children

• Dry mouth and tongue
• No tears when crying
• No wet diapers for 3 hours or more
• Sunken abdomen, eyes, or cheeks
• High fever
• Listlessness or irritability
• Skin that does not flatten when pinched and released

National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, U.S. Department of Health and Human Services.

The removal of water; in chemistry, the loss of two hydrogen atoms for every oxygen atom (see H).

1. The purposeful removal of water from a food product, usually by the action of heat and/or vacuum.
   
2. The accidental or ancillary loss of water developed upon standing or in contact with another substance, packaging, environmental, or chemical influence. See Spray Drying, Drying Techniques, Syneresis.1.
   

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1. the removal of combined, or adsorbed, water from a chemical compound; see also anhydrous.
2. the process or result of losing water, especially the abnormal loss of water from an organism.
3. the replacement of water by solvents.

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The state when the body loses more water than it takes in. There is a negative fluid balance, so that the circulating blood volume decreases and tissue fluids are reduced and tissues are dehydrated. The clinical syndrome of dehydration includes loosening and wrinkling of the skin, and a bad skin-tenting reaction, in which a pinched-up fold of skin takes longer than normal to disappear; there is usually evidence of the cause of the dehydration, e.g. vomiting, polyuria. Clinical pathological tests are essential to determine the severity of the dehydration.

• cellular d. — caused by increased osmoconcentration of the extracellular fluid.

(dē′hīdrā′shən)
n

1. the removal of water (for example, from the body or tissue). n 2. a decrease in serum fluid coupled with the loss of interstitial fluid from the body. Dehydration is associated with disturbances in fluid and electrolyte balance.

For a list of words related to dehydration, see:

• Afflictions and Conditions - dehydration: deficiency or loss of water in body tissues marked by thirst, nausea, and exhaustion
• Business and Science of Agriculture - dehydration: process of removing water from soil or products

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