Dehydration

Definition

Dehydration occurs when you lose more fluid than you take in, and your body doesn't have enough water and other fluids to carry out its normal functions. If you don't replace lost fluids, you may get dehydrated.
Common causes of dehydration include intense diarrhea, vomiting, fever or excessive sweating. Not drinking enough water during hot weather or exercise also may cause dehydration. Anyone may become dehydrated, but young children, older adults and people with chronic illnesses are most at risk.
You can usually reverse mild to moderate dehydration by drinking more fluids, but severe dehydration needs immediate medical treatment. The safest approach is prevention of dehydration. Monitor your fluid loss during hot weather, illness or exercise, and drink enough liquids to replace what you lose.

Symptoms

Mild to moderate dehydration is likely to cause:

• Dry, sticky mouth
• Sleepiness or tiredness — children are likely to be less active than usual
• Thirst
• Decreased urine output — no wet diapers for three hours for infants and eight hours or more without urination for older children and teens
• Few or no tears when crying
• Dry skin
• Headache
• Constipation
• Dizziness or lightheadedness

Severe dehydration, a medical emergency, can cause:

• Extreme thirst
• Extreme fussiness or sleepiness in infants and children; irritability and confusion in adults
• Very dry mouth, skin and mucous membranes
• Lack of sweating
• Little or no urination — any urine that is produced will be dark yellow or amber
• Sunken eyes
• Shriveled and dry skin that lacks elasticity and doesn't "bounce back" when pinched into a fold
• In infants, sunken fontanels — the soft spots on the top of a baby's head
• Low blood pressure
• Rapid heartbeat
• Rapid breathing
• No tears when crying
• Fever
• In the most serious cases, delirium or unconsciousness

Unfortunately, thirst isn't always a reliable gauge of the body's need for water, especially in children and older adults. A better indicator is the color of your urine: Clear or light-colored urine means you're well hydrated, whereas a dark yellow or amber color usually signals dehydration.
When to see a doctor
If you're a healthy adult, you can usually treat mild to moderate dehydration by drinking more fluids, such as water or a sports drink (Gatorade, Powerade, others).
Get immediate medical care if you develop severe signs and symptoms such as extreme thirst, a lack of urination, shriveled skin, dizziness and confusion.
Treat children and older adults with greater caution. Call your family doctor right away if your loved one:

• Develops severe diarrhea, with or without vomiting or fever
• Has bloody stool
• Has had moderate diarrhea for three days or more
• Can't keep down fluids
• Is irritable or disoriented and much sleepier or less active than usual
• Has any of the signs or symptoms of mild or moderate dehydration

Go to the nearest hospital emergency room or call 911 or your emergency medical number if you think a child or older adult is severely dehydrated. You can help prevent dehydration from becoming severe by carefully monitoring someone who is sick and giving fluids, such as an oral rehydration solution (Pedialyte, others) at the first sign of diarrhea, vomiting or fever and by encouraging children to drink plenty of water before, during and after exercise.

Causes

Dehydration occurs when there isn't enough water to replace what's lost throughout the day. Your system literally dries out. Sometimes dehydration occurs for simple reasons: You don't drink enough because you're sick or busy, or because you lack access to safe drinking water when you're traveling, hiking or camping.
Other dehydration causes include:

• Diarrhea, vomiting. Severe, acute diarrhea — that is, diarrhea that comes on suddenly and violently — can cause a tremendous loss of water and electrolytes in a short amount of time. If you have vomiting along with diarrhea, you lose even more fluids and minerals. Children and infants are especially at risk.
• Fever. In general, the higher your fever, the more dehydrated you may become. If you have a fever in addition to diarrhea and vomiting, you lose even more fluids.
• Excessive sweating. You lose water when you sweat. If you do vigorous activity and don't replace fluids as you go along, you can become dehydrated. Hot, humid weather increases the amount you sweat and the amount of fluid you lose. But you can also become dehydrated in winter if you don't replace lost fluids. Preteens and teens who participate in sports may be especially susceptible, both because of their body weight, which is generally lower than that of adults, and because they may not be experienced enough to know the warning signs of dehydration.
• Increased urination. This is most often the result of undiagnosed or uncontrolled diabetes mellitus, a disease that affects the way your body uses blood sugar. This type of diabetes often causes increased thirst and more frequent urination. Another type of diabetes, diabetes insipidus, also is characterized by excessive thirst and urination, but in this case the cause is a hormonal disorder that makes your kidneys unable to conserve water. Certain medications — diuretics, antihistamines, blood pressure medications and some psychiatric drugs — as well as alcohol also can lead to dehydration, generally because they cause you to urinate or perspire more than normal.

Risk factors

Anyone can become dehydrated if they lose too many fluids. But certain people are at greater risk, including:

• Infants and children. Infants and children are especially vulnerable because of their relatively small body weights and high turnover of water and electrolytes. They're also the group most likely to experience diarrhea.
• Older adults. As you age, you become more susceptible to dehydration for several reasons: Your body's ability to conserve water is reduced, your thirst sense becomes less acute and you're less able to respond to changes in temperature. What's more, older adults, especially people in nursing homes or living alone, tend to eat less than younger people do and sometimes may forget to eat or drink altogether. Disability or neglect also may prevent them from being well nourished. These problems are compounded by chronic illnesses such as diabetes, by hormonal changes associated with menopause and by the use of certain medications.
• People with chronic illnesses. Having uncontrolled or untreated diabetes puts you at high risk of dehydration. But other chronic illnesses also make you more likely to become dehydrated. These include kidney disease, alcoholism and adrenal gland disorders. Even having a cold or sore throat makes you more susceptible to dehydration because you're less likely to feel like eating or drinking when you're sick. A fever increases dehydration even more.
• Endurance athletes. Anyone who exercises can become dehydrated, especially in hot, humid conditions or at high altitudes. But athletes who train for and participate in ultramarathons, triathlons, mountain climbing expeditions and cycling tournaments are at particularly high risk. That's because the longer you exercise, the more difficult it is to stay hydrated. During exercise, your body may lose more water than it can absorb. With every hour you exercise, your fluid debt increases. Dehydration is also cumulative over a period of days, which means you can become dehydrated with even a moderate exercise routine if you don't drink enough to replace what you lose on a daily basis.
• People living at high altitudes. Living, working and exercising at high altitudes (generally defined as above 8,200 feet, or about 2,500 meters) can cause a number of health problems. One is dehydration, which commonly occurs when your body tries to adjust to high elevations through increased urination and more rapid breathing — the faster you breathe to maintain adequate oxygen levels in your blood, the more water vapor you exhale.
• People working or exercising outside in hot, humid weather. When it's hot and humid, your risk of dehydration and heat illness increases. That's because when the air is humid, sweat can't evaporate and cool you as quickly as it normally does, and this can lead to an increased body temperature and the need for more fluids.

Complications

Dehydration can lead to serious complications, including:

• Heat injury. If you don't drink enough fluids when you're exercising vigorously and perspiring heavily, you may end up with a heat injury, ranging in severity from mild heat cramps to heat exhaustion to potentially life-threatening heatstroke.
• Swelling of the brain (cerebral edema). Sometimes, when you're getting fluids again after being dehydrated, the body tries to pull too much water back into your cells. This can cause some cells to swell and rupture. The consequences are especially grave when brain cells are affected.
• Seizures. Electrolytes — such as potassium and sodium — help carry electrical signals from cell to cell. If your electrolytes are out of balance, the normal electrical messages can become mixed up, which can lead to involuntary muscle contractions and sometimes to a loss of consciousness.
• Low blood volume shock (hypovolemic shock). This is one of the most serious, and sometimes life-threatening, complications of dehydration. It occurs when low blood volume causes a drop in blood pressure and a drop in the amount of oxygen in your body.
• Kidney failure. This potentially life-threatening problem occurs when your kidneys are no longer able to remove excess fluids and waste from your blood.
• Coma and death. When not treated promptly and appropriately, severe dehydration can be fatal.

Tests and diagnosis

Your doctor can often diagnose dehydration on the basis of physical signs and signs and symptoms such as little or no urination, sunken eyes, and skin that lacks its normal elasticity and resilience when pinched. If you're dehydrated, you're also likely to have low blood pressure, especially when moving from a lying to a standing position, a faster than normal heart rate and reduced blood flow to your extremities.
To help confirm the diagnosis and pinpoint the degree of dehydration, you may have other tests, such as:

• Blood tests. Blood samples may be used to check for a number of factors, such as the levels of your electrolytes — especially sodium and potassium — and how well your kidneys are working.
• Urinalysis. Tests done on your urine can help show whether you're dehydrated and to what degree.

If it's not obvious why you're dehydrated, your doctor may order additional tests to check for diabetes and for liver or kidney problems.