Dehydration, also called hypohydration, is a condition in which the body loses too much water, usually as a result of excess sweating, vomiting, and/or diarrhea. Hydration describes a condition of fluid balance (water homeostasis) when adequate fluid levels are maintained. When fluid balance is not maintained, an individual is said to be dehydrated. Water is very important to the human body because about 75% of the body's weight is due to water. A person that is dehydrated and not drinking water can only live for about 10 days. Medical studies have shown that most Americans are underhydrated and should drink more water each day. Exercising or participating in sporting events can sometimes result in dehydration if sufficient water is not consumed to replace fluids lost by the sweating process.
Dehydration occurs when more fluid is lost from the body than is taken in. Water is essential to life. Body functions such as transporting nutrients, removing wastes, regulating body temperature, and lubricating of joints and membranes, as well as the chemical reactions that occur during cellular metabolism, all require water.
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%, newborns have about 80%, infants have an estimated 77%, and the elderly have 46%–52%. An increase in body fat causes a decrease in the percent age of fluid content because fat does not contain significant amounts of water.
Healthy people lose water through urination, elimination of solid wastes, sweating, and breathing out water vapor. This water must be replaced through the diet. The U.S. Institute of Medicine (IOM) recommended in 2004 (which is still accurate as of 2012) that relatively inactive adult men take in about 125 oz. (3.7 L, about 15 cups) of fluids daily and that women take in about 91 oz. (2.7 L, about 10 cups) to replace lost water. These recommendations are for total fluid intake from both beverages and food. Highly active adults, such as those that participate regularly in sporting events or athletic competitions, and those living in very warm climates need more fluid.
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:
Dehydration involves more than just water deficiency. Electrolytes are ions that form when salts dissolve in water or body fluids. In order for cells to function adequately, 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. Athletes and others that participate in exercises are often told to consume water or sports drinks. Sports beverages, such as the branded Gatorade, Powerade, and 10K Thirst Quencher, are designed to help rehydrate the body when fluids and electrolytes are depleted during strenuous physical activities. For instance, it is noticeable during professional National Football League (NFL) football games that players are given fluids when leaving the field of play.
Risk factors for dehydration in the general population include:
Risk factors for dehydration in seniors include:
There are three basic types of dehydration, defined by the sodium/water balance in body fluids. Doctors who are treating patients with dehydration must determine the type of water loss 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. Isotonic dehydration 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 is 135–145 mmol/L, where mmol stands for millimoles). 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 and 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 (irregular 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.
Diarrhea, often accompanied by vomiting, is the leading cause of dehydration. Both water and electrolytes are lost in large quantities. Bacteria, viruses, or parasites often cause diarrhea. Fever that often accompanies disease accelerates the amount of water that is lost through the skin. For children, their smaller size means the greater the risk of dehydration. Worldwide, acute diarrhea accounts for the death of about 4 million children each year. The World Health Organization (WHO) and the United Nations Children's Fund (UNICEF) state that about 1.5 million children under the age of five years die annually from acute diarrhea. In the United States, about 220,000 children are hospitalized for dehydration caused by diarrhea annually.
Heavy sweating also causes dehydration and loss of electrolytes. Athletes, especially endurance athletes and individuals with active outdoor professions, such as roofers and road crew workers, are at high risk of becoming dehydrated. Children who play sports outdoors can also be vulnerable to dehydration.
Certain chronic illnesses that disrupt fluid balance can cause dehydration. Kidney disease and hormonal disorders, such as diabetes or adrenal or pituitary gland disorders, can cause fluid and electrolyte loss through excessive urination. Such disorders as cystic fibrosis or other genetic disorders resulting in inadequate absorption of nutrients from the intestines can cause chronic diarrhea that leads to dehydration. Individuals with eating disorders who abuse laxatives, diuretics, or enemas or who regularly cause themselves to vomit are vulnerable to severe electrolyte imbalances and dehydration. The same is true of people with alcoholism. People who have severe burns over a large part of their body also are likely to become dehydrated because they no longer have unbroken skin to act as a barrier to evaporation.
Dehydration can be mild, moderate, or severe. Mild dehydration occurs when fluid losses equal 3%–5%. At this point, the thirst sensation is felt, and is often accompanied by dry mouth and thick saliva.
Severe dehydration occurs when fluid losses are 10% or more of their body weight. Severe dehydration is a medical emergency for individuals of any age. A loss of fluids equaling 15%–20% of a person's body weight is fatal. Signs of severe dehydration include all those of moderate dehydration as well as lack of sweating, little or no urine production, dry skin that has little elasticity, low blood pressure, rapid heartbeat, fever, delirium, or coma.
Mild dehydration can often be treated at home. However, a doctor should be consulted whenever:
A doctor's diagnosis of dehydration includes taking a recent health history, checking especially for the presence of specific illnesses, vomiting, diarrhea, constipation, fever, or such other noticeable symptoms as less frequent urination or lack of thirst. The doctor will also want to know about chronic illnesses and current medications.
In addition to taking the patient's history, dehydration is diagnosed by a physical examination. A healthcare professional or observant adult can usually tell if someone is moderately or severely dehydrated by simply looking at them. Visual signs are often enough to begin treatment.
Laboratory tests are important indicators of dehydration; blood tests include complete blood count (CBC), blood chemistries such as electrolytes (e.g., sodium, potassium, chloride), blood urea nitrogen (BUN), and creatinine, among others. Examination of urine and measurement of a 24-hour urine sample may be done to determine if output is normal or decreased. Heart rate and blood pressure will be measured and an electrocardiogram may be taken to see if heart rhythm is altered. In hospitalized patients with possible dehydration, fluid intake and output may be measured to determine if kidney function is impaired.
Other laboratory tests may be ordered to determine if an underlying condition (e.g., diabetes or an adrenal gland disorder) is the cause of the dehydration.
The goal of treatment is to restore fluid and electrolyte balance. For individuals with mild dehydration, this can be done in infants and children by giving them oral rehydration solutions, such as the branded products Pedialyte, Infalyte, Naturalyte, Oralyte, or Rehydralyte. These are available in supermarkets and pharmacies without a prescription. These solutions have the proper balance of salts and sugars to restore the electrolyte balance. Water, apple juice or other juices, chicken broth, and similar fluids are effective in treating mild dehydration. Oral rehydration fluids can be given to young children in small sips as soon as vomiting and diarrhea start. They may continue to vomit and have diarrhea, but some of the fluid will be absorbed.
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 breastfed 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.
Older children who are dehydrated can be given oral rehydration solutions or sports drinks such as Gatorade for moderate and severe dehydration; otherwise, general fluids are fine. Athletes who are dehydrated should be given sports drinks. 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. Adults who are mildly or moderately dehydrated usually improve by drinking water and avoiding coffee, tea, and soft drinks that contain caffeine.
Individuals of all ages who are seriously dehydrated need to be treated by a medical professional. In the case of severe dehydration, the individual may be hospitalized and fluids given intravenously (IV; directly into the vein). Hospital care will include not only immediate replacement of fluids but may also involve treating an underlying chronic illness, such as diabetes, kidney disease, or heart disease, that has resulted in fluid loss and dehydration.
Treatment of dehydration may involve changing any medications that have caused excessive fluid loss. In some cases, patients may be given antiemetics or antidiarrheal drugs to stop the vomiting or diarrhea that may be causing the dehydration.
People can keep rehydration products in the home in case they are needed. Fluid replacement products that contain essential body chemicals and nutrients are available at pharmacies and some supermarkets; pharmacists can offer advice about the best ones to help correct or prevent dehydration and to restore electrolyte balance.
The World Health Organization recommends a homemade solution to help the dehydrated person correct fluid levels and also receive needed sugars and nourishment. To rehydrate the body, the following ingredients can be combined and sipped frequently over several hours:
Mild dehydration rarely results in complications. It can usually be reversed by correcting fluid levels through drinking or receiving fluids intravenously. If the cause is eliminated and lost fluid is replaced, mild dehydration can usually be resolved in 24 to 48 hours.
On the other hand, 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. Imbalances in the electrolyte sodium can cause too much water to be absorbed by brain cells, causing them to swell and rupture—a serious complication of dehydration. Underlying chronic diseases can complicate the correction of dehydration, resulting in organ system dysfunction. Severe dehydration can lead to shock and kidney failure, which can be life threatening.
Preventing dehydration is easier than treating it once it occurs. Drinking eight glasses of water a day prevents dehydration. More may be needed in hot weather. Beginning each day with a glass of water containing a small amount of lemon or other citrus juice helps restore fluid and blood sugar (glucose) levels that have diminished overnight. Water and other clear liquids (decaffeinated/herbal tea, juices, and clear soups) can be consumed slowly throughout the day rather than drinking too much at mealtimes, which will dilute digestive juices. Alcoholic beverages and excessive amounts of caffeine-containing drinks, which dehydrate the body, should be avoided.
Studies have shown that people at work tend to drink less water than those performing other pursuits. Oftentimes, headaches occur while working because of a lack of water. Because many experts contend most Americans are underhydrated, it is good practice to consume small amounts of water throughout the workday. In fact, it is good practice to do so in any situation, whether at work or play.
Another way to prevent dehydration is to be alert to situations in which it could occur, such as exercising in hot weather or vomiting and diarrhea in infants and young children. Athletes and people who work in hot conditions should drink regularly whether or not they feel thirsty. Rehydration of young children should begin at the first sign of fluid loss. A health-care provider should be consulted before the situation becomes serious.
Besides drinking to restore fluid balance, normal consumption of food is necessary when someone is dehydrated. Because intestinal upsets with either diarrhea or vomiting can result in loss of interest in eating or the temporary inability to keep food down or digest it, foods should be kept simple and as soft or liquid as possible, including weak tea, broth, bouillon, plain soups, and lightly cooked vegetables. Large amounts of fluids should not be consumed all at once, as this delays gastric emptying and encourages urination. It is recommended that dehydrated individuals sip fluids in small amounts at frequent intervals (e.g., 3.5–7.0 oz. [about 100–200 mL] every 20 minutes) to achieve effective rehydration. Flavored gelatin is often a good fluid replacement and is easy to digest. Such high-fiber foods as whole fruit, bread, grains, and meat should be avoided until the intestinal tract has had a rest. Milk is not a clear liquid and may not be tolerated; milk is not ideal for fluid replacement. Caffeine-containing drinks and alcohol encourage excess urination and should be avoided.
See also Hydration .
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Tish Davidson, AM
Revised by Rebecca J. Frey, PhD
Revised by William A. Atkins, BB, BS, MBA