Causes and Symptoms (Magill’s Medical Guide, Sixth Edition)
The average adult’s total body weight is approximately 60 percent water. Daily water requirements vary based on age, gender, level of physical activity, and climate. Dehydration, loss of 3 percent or more of body weight from the rapid loss of water, is often accompanied by the loss of essential electrolytes such as sodium, potassium, and chloride. Conditions that deplete body water faster than it is absorbed include fever-induced sweating, diarrhea, vomiting, acidosis, anorexia nervosa, bulimia, diabetes mellitus and insipidus, undernutrition, obesity, a sedentary lifestyle, and lack of acclimatization to heat stress. People exercising in hot, humid environments provide an excellent example of how dehydration develops and progresses. Symptoms of dehydration may include dry mouth, lips, and skin; decreased salivation; dizziness; weakness; constipation; and confusion.
Heat gain is higher and evaporative heat loss is lower during physical exertion in a hot environment in children as compared to adults, predisposing children to more rapid and severe dehydration. Both child and adult bodies attempt to reduce the buildup of metabolic heat through blood flow adjustments and sweat gland secretion. Flushed, red skin indicates that peripheral blood vessels have dilated, carrying blood and internal heat to the body surface for cooling. Once the heat is carried to the periphery by the bloodstream, dissipation occurs mainly by sweat...
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Treatment and Therapy (Magill’s Medical Guide, Sixth Edition)
Rapid restoration of fluid volume and electrolyte balance are primary treatment goals that may require intravenous infusion if sufficient fluid cannot be ingested orally.
“Prehydrating” the body by consuming liberal amounts of fluid before anticipated heat stress and “trickle hydrating” while losing body fluid are critical. Cool fluids of about 40 degrees Fahrenheit (about 5 degrees Celsius) empty from the gastrointestinal tract and supply the dehydrated cells quicker than warmer or colder temperature fluid. Studies of fluid absorption indicate that excessive sugar in electrolyte drinks slows water movement into the bloodstream. Children have been shown voluntarily to drink nearly twice as much when flavored fluids, as compared to plain water, are allowed.
Monitoring body weight before and after dehydration episodes and drinking enough water to regain lost weight is important. Nearly all body weight lost during exercise is attributable to water loss, not fat loss. Consuming 1 pint (473 milliliters) of fluid will replenish 1 pound (9.45 kilograms) of water weight loss. People should drink back all lost water weight even though they may not feel thirsty, as the human thirst mechanism is not a good indicator of actual need. Checking the urine is also recommended, as dark yellow urine indicates that more water consumption is needed and nearly colorless urine indicates that adequate rehydration has been...
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Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
Many episodes of dehydration can be prevented from developing into heat cramps, heat exhaustion, and heatstroke during sporting events by adhering to the aforementioned guidelines. Heat cramps, especially muscle spasms in the calves and stomach, may occur during intense sweating, with the accompanying loss of electrolytes. Mineral loss, however, is always of secondary importance to fluid loss because water provides the medium in which all cellular processes occur.
Heat exhaustion occurs when increased sweating and peripheral blood flow reduce venous return of blood to the heart, resulting in cool and clammy skin, lower-than-normal blood pressure, and a rapid but weak heart rate. Less blood is pumped to the brain, causing weakness, faintness, dizziness, headaches, and a grayish look to the face. Treatment includes lying down in a shaded, breezy place, drinking cool fluids, and removing excess clothing. Heatstroke occurs when the brain can no longer maintain thermal balance, as evidenced by the cessation of sweating, hot (sometimes white to gray) skin, rapid and full pulse, and a rise in body temperature over 104 degrees Fahrenheit leading to disorientation and unconsciousness. Heatstroke is rare but requires immediate medical attention to reduce body temperature. The body temperature should be lowered quickly by placing ice packs to the groin, neck, and under the arms. Cool sheets may be placed over and under the...
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Brody, Jane E. “For Lifelong Gains, Just Add Water. Repeat.” The New York Times, July 11, 2000, p. F8. The average American consumes slightly more than half the recommended amount of water per day. To avoid the symptoms of dehydration (headache, lethargy, dizziness, mental fuzziness, and loss of appetite), one should drink at least eight glasses of water per day.
McArdle, William, Frank I. Katch, and Victor L. Katch. Exercise Physiology: Energy, Nutrition, and Human Performance. 7th ed. Boston: Lippincott Williams & Wilkins, 2010. A wide-ranging text on exercise and the human body, covering topics such as nutrition, energy transfer, exercise training, systems of energy delivery and utilization, enhancement of energy capacity, the effect of environmental stress, and the effect of exercise on successful aging and disease prevention.
Sawka, Michael N., Samuel N. Cheuvront, and Robert Carter. “Human Water Needs.” Nutrition Reviews 63, no. 6 (June, 2005): S30-S39. Provides information on daily water needs and the estimated amount of water intake required by an average adult male.
Sawka, Michael N., and Scott J. Montain. “Fluid and Electrolyte Supplementation for Exercise Heat Stress.” American Journal of Clinical Nutrition 72, no. 2S (August, 2000): S564-S572. During exercise in the heat, sweat output often exceeds water intake, resulting in a body water...
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Dehydration (Encyclopedia of Medicine)
Dehydration is the loss of water and salts essential for normal body function.
Dehydration occurs when the body loses more fluid than it takes in. This condition 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. Dehydration can upset the delicate fluid-salt balance needed to maintain healthy cells and tissues.
Water accounts for about 60% of a man's body weight. It represents about 50% of a woman's weight. Young and middle-aged adults who drink when they're thirsty do not generally have to do anything more to maintain their body's fluid balance. Children need more water because they expend more energy, but most children who drink when they are thirsty get as much water as their systems require.
Age and dehydration
Adults over the age of 60 who drink only when they are thirsty probably get only about 90% of the fluid they need. Developing a habit of drinking only in response to the body's thirst signals raises an older person's risk of becoming dehydrated. Seniors who have relocated to areas where the weather is warmer or dryer than the climate they are accustomed to are even likelier...
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Dehydration (Encyclopedia of Children's Health)
Dehydration is the loss of water and salts that are essential for normal body function.
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...
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Dehydration (Encyclopedia of Nursing & Allied Health)
Dehydration is the excessive loss of water from body tissues accompanied by an imbalance in essential electrolytes, such as sodium, potassium, and chloride.
Dehydration occurs when the body loses more fluid than it takes in. Dehydration can be caused by illness, injury, infection, prolonged exposure to sun or high temperatures, inadequate water intake, or overuse of diuretics or other medications that increase urination.
Water is distributed throughout three compartments in the body: inside the cells (intracellular), in the tissue (interstitial), and in the bloodstream (intravascular). Each compartment contains differing amounts of electrolytes that must remain in balance in order for body organs and systems to function correctly. Dehydration upsets this delicate balance. Total body water also varies in relation to age, gender, and amount of body fat. Adult males have approximately 60% water content, adult females have 50%, infants have an estimated 77%, and the elderly have 46% to 52%. An increase in body fat causes a decrease in the percent fluid content because fat does not contain significant amounts of water.
Causes and symptoms
Different types of dehydration have different causes. When managing patients with dehydration, the type of water loss must be determined to ensure appropriate treatment. In addition, water and sodium levels in the body are closely related; if one is abnormal, the other often is too.
Isotonic dehydration is an equal loss of water and sodium. Isotonic means that the number of particles contained on one side of a permeable membrane is the same as on the other side, thus there is no fluid shift in either direction. The amount of intracellular and extracellular water remains in balance. This can be caused by a complete fast, vomiting, and diarrhea.
Hypertonic dehydration occurs when water loss is greater than sodium loss. Blood sodium levels may be >145 mmol/l (normal range=135 to 145 mmol/l). Higher blood sodium levels combined with decreased water in the intravascular space increases the osmotic pressure in the bloodstream, which, in turn, pulls more fluid out of the cells. This type of dehydration is usually caused by extended fever with limited oral rehydration. Mortality is more likely to occur from hypertonic than from isotonic dehydration.
Hypotonic dehydration occurs when sodium loss is greater than water loss. Blood sodium levels may be less than 135 mmol/l; and the osmotic pressure is greater inside the cells, which pulls more fluid out of the intravascular space into the intracellular space. This type of dehydration occurs with overuse of diuretics, which causes excessive sodium and potassium loss. Potassium depletion affects respiration, increases nausea, and, if severe enough, may cause respiratory arrest or central nervous system (CNS) seizures. Potassium depletion may also cause arrhythmias (an alteration in the heartbeat). As a result, patients are told to take diuretics with orange juice or to eat a banana, both of which are high in potassium.
Strenuous activity, excessive sweating, prolonged time in the sun, and extended vomiting or diarrhea cause fluid loss. Elderly people who move to warm, dry climates frequently become dehydrated because of the climate change combined with a tendency to not drink enough water. Large amounts of fluid can also be lost from prolonged fever. Healthy people require about 1 milliliter of water for each calorie their body metabolizes; but during a fever the metabolic rate increases by seven percent for each 1°F rise in body temperature. Fever also increases the respiratory rate, resulting in additional water loss from the lungs. Further causes of fluid loss that may be overlooked include caffeine and alcohol consumption, which increase urination and fluid excretion.
Decreased oral intake of fluids is a common cause of dehydration and often occurs during times of appetite loss from illness or after oral surgery or injury. The elderly are at high risk for decreased intake because their thirst mechanism may no longer function or they may be physically unable to get a drink. Infants, another high-risk group, are more likely to develop dehydration than adults because they have a higher metabolic rate and their immature kidneys have difficulty concentrating urine. Children who do not wet their diapers for three hours or more are dehydrated. Dehydration is also associated with disorders of the adrenal glands, which regulate water-electrolyte balance; diabetes mellitus; eating disorders; renal disease; and chronic lung disease.
Symptoms of dehydration at any age may include some or all of the following: cracked lips, dry or sticky mucous membranes, sunken eyes, lethargy, and/or confusion. Urine output is minimal and the skin loses its elasticity (turgor) and is slow to return to its normal position after being raised off the back of the hand (tenting). The heart rate and respiratory rate may be elevated. A dehydrated infant may not shed tears when crying and may have a depressed fontanel (soft spot on their head), although recent studies have shown that a depressed fontanel is not an accurate indicator of dehydration.
The general diagnosis of dehydration can be made based on the patient's symptoms and medical history. Physical examination may reveal any of the symptoms mentioned above, along with shock, rapid heart rate, and low blood pressure. Blood tests are required to determine what deficiency exists (or what is elevated) so that therapy for electrolyte replacement can be planned. Blood tests to check electrolyte levels and urine tests such as urine specific gravity are used to evaluate the severity of the fluid loss. Other laboratory tests may be ordered to determine if an underlying condition (e.g., diabetes or an adrenal gland disorder) is the cause.
Increased fluid intake and replacement of lost electrolytes are usually sufficient to restore fluid balance in patients who are mildly or moderately dehydrated. For individuals who are mildly dehydrated, just drinking plain water may be all the treatment that is needed. Adults may replace lost electrolytes by drinking sports beverages, such as Gatorade or Recharge. Parents should follow label instructions when giving children Pedialyte or other commercial products recommended for the treatment of dehydration in children. Children who are dehydrated should be given only clear fluids for the first 24 hours.
A child who is vomiting should sip one or two teaspoons of liquid every 10 minutes. A child who is less than a year old and who is not vomiting should be given one tablespoon of liquid every 20 minutes. A child who is more than one year old and who is not vomiting should take two tablespoons of liquid every 30 minutes. A baby who is being breast-fed should be given clear liquids for two consecutive feedings before breastfeeding is resumed. A bottle-fed baby should be given formula diluted with water to half the formula strength for the first 24 hours after symptoms of dehydration are identified.
To calculate fluid loss accurately, weight changes should be charted every day and a record kept of how many times a patient vomits or has diarrhea. A record of fluid output (including sputum or vomit) and of fluid intake or replacement should be kept for at least 24 to 48 hours to see if balance is being accomplished. Parents should note how many times a baby's diaper must be changed. If dehydration continues, emergency department treatment or hospitalization to receive intravenous fluids and electrolytes may be necessary.
Children and adults can gradually return to their normal diet after they have stopped vomiting and no longer have diarrhea. Gelatin is often a welcomed substitute for additional water and does count as fluid replacement. Bland foods should be reintroduced first, with other foods added as the digestive system is able to tolerate them. Milk, ice cream, cheese, and butter should not be eaten until 72 hours after symptoms have disappeared.
When treating dehydration, the underlying cause must be addressed. For example, if dehydration is caused by vomiting or diarrhea, medications should be prescribed to resolve these symptoms. Patients who are dehydrated due to diabetes, kidney disease, or adrenal gland disorders must receive treatment for these conditions as well as for the resulting dehydration. If dehydration is being caused by diuretics. a dose adjustment made by the physician or a change to a different diuretic may be necessary.
Mild dehydration rarely results in complications. If the cause is eliminated and lost fluid is replaced, mild dehydration can usually be resolved in 24 to 48 hours. Vomiting and diarrhea that continue for several days without adequate fluid replacement can be fatal since more is lost than water and sodium. Severe potassium loss may lead to cardiac arrhythmias, respiratory distress or arrest, or convulsions (seizures). The risk of life-threatening complications is greater for young children and the elderly. However, dehydration that is rapidly recognized and treated has a good outcome.
Health care team roles
The nurse and the physician have the greatest responsibility in recognizing and treating dehydration. For hospitalized patients, the physician should order appropriate fluid and electrolyte replacement and the nurse should ensure that the correct fluids are given to the patient. The nurse should monitor the patient for signs that the dehydration (e.g., decrease in fever, increase in blood pressure, reduced heart rate) is resolving and should notify the physician if it is not.
Blood tests used to diagnose dehydration are collected by specially trained nursing assistants or by laboratory technicians. Outpatient samples in a physician's office may be taken by the nurse or a technician. In some institutions, the nurse collects the blood sample. Usually, urine samples are collected by the nurse, and results calculated by the laboratory technician.
Patients who are vomiting or who have diarrhea can prevent dehydration by drinking enough fluid to keep their urine the color of pale straw. Infants and young children with diarrhea and vomiting can be given electrolyte solutions such as Pedialyte to help prevent dehydration, as well as suppository medication to stop the vomiting. People who are not ill can maintain proper fluid balance by drinking several glasses of water before going outside on a hot day. It is also a good idea to avoid coffee and tea, which increase body temperature and water loss.
Patients should ask a pharmacist whether or not any medications they are taking may cause dehydration and what to do to prevent it other than adequate fluid intake. Prompt medical attention should be sought to correct any underlying condition that increases the risk of dehydration.
Extracellularutside the cells.
Hypertonicne solution having a greater amount of solute (dissolved substance in a solution) than another solution, thus it exerts more osmotic pressure than the second solution and the body will attempt to equalize pressure by passing fluid through the cell membranes.
Hypotonicne solution having a lesser amount of solute than another solution, thus it exerts less osmotic pressure than the second solution.
Intracellularnside the cells.
Isotonicwo solutions exerting the same amount of osmotic pressure on a cell membrane.
Osmotic pressurehe pressure exerted on a semipermeable membrane that separates two solutions and the particles they contain.
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