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Dehydration means your body does not have as much water and fluids as it should. Dehydration can be caused by losing too much fluid, not drinking enough water or fluids, or both. Vomiting and diarrhea are common causes.

Infants and children are more susceptible to dehydration than adults because of their smaller body weights and higher turnover of water and electrolytes. The elderly and those with illnesses are also at higher risk.

Dehydration is classified as mild, moderate, or severe based on how much of the body's fluid is lost or not replenished. When severe, dehydration is a life-threatening emergency.

Your body may lose too much fluids from:

• Vomiting or diarrhea
• Excessive urine output, such as with uncontrolled diabetes or diuretic use
• Excessive sweating (for example, from exercise)
• Fever

• Nausea
• Loss of appetite due to illness
• Sore throat or mouth sores

Dehydration in sick children is often a combination of both -- refusing to eat or drink anything while also losing fluid from vomiting, diarrhea, or fever.

• Dry or sticky mouth
• Low or no urine output; concentrated urine appears dark yellow
• Not producing tears
• Sunken eyes
• Markedly sunken fontanelles (the soft spot on the top of the head) in an infant
• Lethargic or comatose (with severe dehydration)

A physical examination may also show signs of:

• Low blood pressure
• Blood pressure that drops when you go from lying down to standing
• Rapid heart rate
• Poor skin turgor -- the skin may lack its normal elasticity and sag back into position slowly when pinched up into a fold by the doctor; normally, skin springs right back into position
• Delayed capillary refill
• Shock

• Blood chemistries (to check electrolytes, especially sodium, potassium, and bicarbonate levels)
• Urine specific gravity (a high specific gravity indicates significant dehydration)
• BUN (blood urea nitrogen -- may be elevated with dehydration)
• Creatinine (may be elevated with dehydration)
• Complete blood count (CBC) to look for signs of concentrated blood

When dehydration is recognized and treated promptly, the outcome is generally good.

Untreated severe dehydration may result in seizures, permanent brain damage, or death.

Call 911 if you or your child have the following symptoms

• Dizziness
• Lightheadedness
• Lethargy
• Confusion

Call your doctor right away if you or your child has any of the following symptoms:

• Not producing tears
• Sunken eyes
• Little or no urine output for 8 hours
• Dry skin that sags back into position slowly when pinched up into a fold
• Dry mouth or dry eyes
• Sunken soft-spot on the top of your infant's head
• Fast-beating heart
• Blood in the stool or vomit
• Diarrhea or vomiting (in infants less than 2 months old)
• Listlessness and inactiveness

Also call your doctor if you are not sure whether your attempts to give your child proper fluids are working.

• An illness is combined with the inability to keep down any fluids
• Vomiting has been going on for longer than 24 hours in an adult or longer than 12 hours in a child
• Diarrhea has lasted longer than 5 days in an adult or child
• Your infant or child is much less active than usual or is irritable
• You or your child have excessive urination, especially if there is a family history of diabetes or you are taking diuretics

Even when healthy, drink plenty of fluid every day. Drink more when the weather is hot or you are exercising.

Carefully monitor someone who is ill, especially an infant, child, or older adult. If you believe that dehydration is developing, consult a doctor before the person becomes moderately or severely dehydrated. Begin fluid replacement as soon as vomiting and diarrhea start -- DO NOT wait for signs of dehydration.

Always encourage the person to drink during an illness, and remember that a person's fluid needs are greater when that person has fever, vomiting, or diarrhea. The easiest signs to monitor are urine output (there should be frequent wet diapers or trips to the bathroom), saliva in the mouth, and tears when crying.

Porter SC. The value of parental report for diagnosis and management of dehydration in the emergency department. Ann Emerg Med. 2003; 41(2): 196-205.

Guerrant RL. Practice guidelines for the management of infectious diarrhea. Clin Infec Dis. 2001; 32(3): 331-351.

Committee on Sports Medicine and Fitness. American Academy of Pediatrics. Climatic heat stress and the exercising child and adolescent. Pediatrics. 2000; 106(1 Pt 1): 158-159.