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| ==Overview==
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| '''Dehydration''' ('''hypohydration''') is the removal of [[water]] (''hydro'' in ancient [[Greek language|Greek]]) from an object. [[Medical]]ly, it is a condition in which the body contains an insufficient volume of water for normal functioning.
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| == Causes of Dehydration==
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| In [[human]]s, dehydration can be caused by a wide range of [[disease]]s and states that impair
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| water [[homeostasis]] in the body. These include:
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| * External or [[stress (medicine)|stress]]-related causes
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| ** Prolonged physical activity without consuming adequate water, especially in a hot and/or humid environment
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| ** Prolonged exposure to dry air, e.g., in high-flying airplanes (5-15% r.h.)
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| ** Survival situations, especially desert survival conditions
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| ** [[Blood loss]] or [[hypotension]] due to [[physical trauma]]
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| ** [[Diarrhea]]
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| ** [[Hyperthermia]]
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| ** [[Shock (medical)|Shock]] (hypovolemic)
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| ** [[Vomit]]ing
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| ** [[Burn (injury)|Burns]]
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| ** [[Lacrimation]]
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| * [[Infectious diseases]]
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| ** [[Cholera]]
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| ** [[Gastroenteritis]]
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| ** [[Shigellosis]]
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| ** [[Yellow fever]]
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| * [[Malnutrition]]
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| ** [[Electrolyte disturbance]]
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| *** [[Hypernatremia]] (also caused by dehydration)
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| *** [[Hyponatremia]], especially from restricted [[sodium chloride|salt]] [[Dieting|diet]]s
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| ** Consumption of alcohol, [[caffeine]] or other [[diuretic]] substances.
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| ** [[Fasting]]
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| ** Recent rapid [[weight loss]] may reflect progressive depletion of fluid volume. (The loss of 1 L of fluid results in a weight loss of 1 kg, or 2.2 lb.)<ref>http://www.heartspring.net/symptoms_of_dehydration.html</ref>
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| ** [[Patient refusal of nutrition and hydration]]
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| * Other causes of obligate water loss
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| ** Severe [[hyperglycemia]], especially in [[Diabetes mellitus]]
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| *** [[Glycosuria]]
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| == Symptoms and prognosis ==
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| [[Symptom]]s may include [[headache]]s similar to what is experienced during a hangover, a sudden episode of [[visual snow]], decreased [[blood pressure]] ([[hypotension]]), and [[dizziness]] or [[fainting]] when standing up due to [[orthostatic hypotension]]. Untreated dehydration generally results in [[delirium]], [[unconsciousness]], swelling of the tongue[http://answers.yahoo.com/question/index?qid=20061109213902AATOqs3] and in extreme cases [[death]].
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| Dehydration symptoms generally become noticeable after 2% of one's normal water volume has been lost. Initially, one experiences [[thirst]] and discomfort, possibly along with loss of [[appetite]] and [[dry skin]]. This can be followed by [[constipation]]. Athletes may suffer a loss of performance of up to 30%<ref>{{cite book
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| | last = Bean
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| | first = Anita
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| | title = The Complete Guide to Sports Nutrition
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| | publisher = A & C Black Publishers Ltd.
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| | date = 2006
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| | pages = pp. 81-83
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| | isbn = 0713675586 }}</ref>, and experience [[Flushing (physiology)|flushing]], low endurance, rapid [[heart rate]]s, elevated body temperatures, and rapid onset of [[fatigue (physical)|fatigue]].
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| [[Symptom]]s of mild dehydration include [[thirst]], decreased [[urine]] volume, abnormally dark urine, unexplained tiredness, lack of [[tears]] when [[crying]], [[headache]], dry mouth, and [[dizziness]] when standing due to [[orthostatic hypotension]].
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| In moderate to severe dehydration, there may be no urine output at all. Other symptoms in these states include [[lethargy]] or extreme sleepiness, [[seizure]]s, sunken [[fontanel]] (soft spot) in [[infant]]s, [[fainting]], and sunken eyes.
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| The symptoms become increasingly severe with greater water loss. One's heart and [[respiration (physiology)|respiration]] rates begin to increase to compensate for decreased [[blood plasma|plasma]] volume and [[blood pressure]], while body temperature may rise because of decreased sweating. Around 5% to 6% water loss, one may become groggy or [[sleep]]y, experience headaches or [[nausea]], and may feel tingling in one's limbs ([[paresthesia]]). With 10% to 15% fluid loss, muscles may become spastic, skin may shrivel and wrinkle, vision may dim, urination will be greatly reduced and may become painful, and delirium may begin. Losses greater than 15% are usually fatal.
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| <ref>http://faculty.washington.edu/kepeter/118/notes/pdf-set5/118water-bal-06.htm</ref>
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| == Treatment ==
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| [[Image:Cholera rehydration nurses.jpg|left|thumb|250px|Nurses encouraging this patient to drink an Oral Rehydration Solution to improve dehydration he acquired from [[cholera]].<br/><small>Courtesy:[[Centers for Disease Control and Prevention]]</small>]]
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| The best treatment for minor dehydration is drinking water and stopping fluid loss.
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| Water is preferable to sport drinks and other commercially-sold rehydration fluids, as the balance of electrolytes they provide may not match the replacement requirements of the individual. To stop fluid loss from vomiting and diarrhea, avoid solid foods and drink only clear liquids.<ref>"Healthwise Handbook," Healthwise, Inc., 1999</ref>
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| In more severe cases, correction of a dehydrated state is accomplished by the replenishment of necessary water and [[electrolyte]]s ([[rehydration]], through [[oral rehydration therapy]] or [[intravenous therapy]]). Even in the case of serious lack of fresh water (e.g., at sea or in a desert), drinking seawater or [[urine]] does not help, nor does the consumption of [[alcohol]]. It is often thought that the sudden influx of [[salt]] into the body from seawater will cause the [[cell (biology)|cell]]s to dehydrate and the [[kidney]]s to overload and shut down but it has been calculated that an average adult can drink up to 0.2 liters of seawater per day before the kidneys start to fail.
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| When dehydrated, unnecessary [[sweating]] should be avoided, as it wastes water. If there is only dry food, it is better not to eat, as water is necessary for [[digestion]]. For severe cases of dehydration where [[fainting]], [[unconsciousness]], or other severely inhibiting symptom is present (the patient is incapable of standing or thinking clearly), emergency attention is required. Fluids containing a proper balance of replacement electrolytes are given orally or intravenously with continuing assessment of electrolyte status; complete resolution is the norm in all but the most extreme cases.
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| == Avoiding dehydration ==
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| Dehydration is best avoided by drinking plenty of water. The greater the amount of water lost through perspiration, the more water must be consumed to replace it and avoid dehydration. Since the body cannot tolerate large deficits or excesses in total body water, consumption of water must be roughly concurrent with the loss (in other words, if one is perspiring, one should also be drinking water frequently). Drinking water slightly beyond the needs of the body entails no risk, since the kidneys will efficiently remove any excess water through the urine with a large margin of safety.
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| A person's body, during an average day in a temperate climate such as the United Kingdom, loses approximately 2.5 [[litre]]s of water. This can be through the [[lung]]s as water vapor, through the [[skin]] as [[sweat]], or through the [[kidney]]s as [[urine]]. Some water (a less significant amount, in the absence of [[diarrhea]]) is also lost through the [[bowel]]s. In warm or humid weather or during heavy exertion, however, the water loss can increase by an order of magnitude or more through perspiration;all of which must be promptly replaced. In extreme cases, the losses may be great enough to exceed the body's ability to absorb water from the gastrointestinal tract; in these cases, it is not possible to drink enough water to stay hydrated, and the only way to avoid dehydration is to reduce perspiration (through rest, a move to a cooler environment, etc.).
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| A useful rule of thumb for avoiding dehydration in hot or humid environments or during strenuous activity involves monitoring the frequency and character of urination. If one develops a full bladder at least every 3-5 hours and the urine is only lightly colored or colorless, chances are that dehydration is not occurring; if urine is deeply colored, or urination occurs only after many hours or not at all, water intake may not be adequate to maintain proper hydration.
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| When large amounts of water are being lost through perspiration and concurrently replaced by drinking, maintaining proper electrolyte balance becomes an issue. Drinking fluids that are hypertonic or hypotonic with respect to perspiration may have grave consequences ([[hyponatremia]] or [[hypernatremia]], principally) as the total volume of water turnover increases.
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| If water is being lost through abnormal mechanisms such as [[vomiting]] or [[diarrhea]], an imbalance can develop very quickly into a medical emergency. In fact, the main mechanisms through which diseases such as [[infantile diarrhea]] and [[cholera]] kill their victims are dehydration and loss of electrolytes.
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| During sports events, water stops and water breaks are provided to avoid dehydration of athletes.
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| == See also == | | == See also == |
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| * [[Hypovolemia]], a depletion of blood volume that can be caused by dehydration | | * [[Hypovolemia]], a depletion of blood volume that can be caused by dehydration |
| * [[Water intoxication]] | | * [[Water intoxication]] |
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| ==References==
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| * Ira R. Byock, M.D., ''[http://www.dyingwell.com/prnh.htm Patient Refusal of Nutrition and Hydration: Walking the Ever-Finer Line]''. American Journal Hospice & Palliative Care, pp. 8-13. (March/April 1995)
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| ==Notes== | | ==Notes== |
| <references/> | | <references/> |
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| {{Fluid, electrolyte, acid base metabolic pathology}} | | {{Fluid, electrolyte, acid base metabolic pathology}} |
| {{Endocrine, nutritional and metabolic pathology}} | | {{Endocrine, nutritional and metabolic pathology}} |
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| [[ca:Deshidratació]] | | [[ca:Deshidratació]] |
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| [[zh:脱水]] | | [[zh:脱水]] |
| [[pl:Odwodnienie]] | | [[pl:Odwodnienie]] |
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| [[Category:Electrolyte disturbance]] | | [[Category:Electrolyte disturbance]] |
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| [[Category:Physical examination]] | | [[Category:Physical examination]] |
| [[Category:Primary care]] | | [[Category:Primary care]] |
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