View source for Dehydration

{{DiseaseDisorder infobox |
  Name        = Dehydration |
  ICD10       = {{ICD10|E|86||e|70}} |
  ICD9        = {{ICD9|276.5}} |
}}

{{ three other uses|the medical condition|the removal of water through chemical or physical means|desiccation|the chemical reaction|dehydration reaction|food preservation by dehydration|drying (food)}}

'''Dehydration''' (''hypohydration'') is defined as an excessive loss of [[body fluid]]. It is literally the removal of [[water]] ({{lang-grc|ὕδωρ|hýdōr}}) from an object, however in [[Physiology|physiological]] terms, it entails a deficiency of fluid within an organism. 

There are three main types of dehydration: hypotonic or hyponatremic (primarily a loss of electrolytes, [[sodium]] in particular), hypertonic or hypernatremic (primarily a loss of water), and isotonic or isonatremic (equal loss of water and electrolytes).<ref name=freedehydration>[http://www.thefreedictionary.com/dehydration TheFreeDictionary.com --> dehydration] Citing The American Heritage Science Dictionary 2005. Retrieved on July 2, 2009</ref> In humans, the most commonly seen type of dehydration by far is isotonic (isonatraemic) dehydration which effectively equates with [[hypovolemia]], but the distinction of isotonic from hypotonic or hypertonic dehydration may be important when treating people who become dehydrated. Physiologically, dehydration, despite the name, does not simply mean loss of water, as water and solutes (mainly sodium) are usually lost in roughly equal quantities to how they exist in [[blood plasma]]. In hypotonic dehydration, [[intravascular water]] shifts to the [[extravascular space]], exaggerating intravascular volume depletion for a given amount of total body water loss. Neurological complications can occur in hypotonic and hypertonic states. The former can lead to [[seizure]]s, while the latter can lead to [[osmotic cerebral edema]] upon rapid rehydration.<ref>{{Cite document|url=http://emedicine.medscape.com/article/906999-overview|title=Dehydration|author=Lennox H Huang|date=Nov 3, 2009|publisher=eMedicine|postscript=<!--None-->}}</ref>

==Definition==
[[Hypovolemia]] is specifically a decrease in volume of [[blood plasma]].<ref> [http://www.medterms.com/script/main/art.asp?articlekey=3871 MedicineNet > Definition of Hypovolemia] Retrieved on July 2, 2009</ref><ref>[http://medical-dictionary.thefreedictionary.com/hypovolemia TheFreeDictionary.com --> hypovolemia] Citing Saunders Comprehensive Veterinary Dictionary, 3 ed. Retrieved on July 2, 2009</ref> Furthermore, hypovolemia defines water deficiency only in terms of volume rather than specifically water.

Nevertheless, the conditions usually appear simultaneously.

== Signs and symptoms ==
[[Symptom]]s may include  [[headache]]s similar to what is experienced during a [[hangover]], muscle [[cramps]] (especially leg cramps), 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 and, in extreme cases, [[death]]. 

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]]. [[sportsperson|Athlete]]s may suffer a loss of performance of up to 30%<ref>{{cite book
  | last = Bean
  | first = Anita
  | title = The Complete Guide to Sports Nutrition
  | publisher = A & C Black Publishers Ltd.
  | date = 2006
  | pages = 81–83
  | isbn = 0713675586 }}</ref> and experience [[Flushing (physiology)|flushing]], low endurance, rapid [[heart rate]]s, elevated body temperatures, and rapid onset of [[fatigue (physical)|fatigue]].

[[Symptom]]s of mild dehydration include [[thirst]], decreased [[urine]] volume, abnormally dark urine, unexplained tiredness, irritability, lack of tears when crying, [[headache]], dry mouth, [[dizziness]] when standing due to [[orthostatic hypotension]], and in some cases can cause insomnia.  Blood tests may show [[Human serum albumin#Hyperalbuminemia|hyperalbuminemia]].  Mild dehydration also has been shown to negatively impact people’s moods.  Experiments by the [[USDA]]'s [http://www.ars.usda.gov/main/main.htm Agricultural Research Service] has shown that dehydration is associated with [[confusion]], [[fatigue]], and negative moods. <ref>http://www.ars.usda.gov/is/pr/2009/091123.htm#_top</ref>  Mild dehydration, which includes water losses between 1% and 2%, observed in the experiment are comparable to mild dehydration experienced by people in their everyday lives.  

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 infants, [[fainting]], and sunken eyes.

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. At around 5% to 6% water loss, one may become groggy or sleepy, 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 (decreased skin turgor), vision may dim, urination will be greatly reduced and may become painful, and delirium may begin.  Losses greater than 15% are usually fatal.

In people over age 50, the body’s [[thirst]] sensation diminishes and continues diminishing with age. Many senior citizens suffer symptoms of dehydration. Dehydration along with [[hyperthermia]] results in seniors dying during extreme hot weather.

Diseases of the gastrointestinal tract can lead to dehydration in various ways. Often, dehydration becomes the major problem in an otherwise self-limited illness. Fluid loss may even be severe enough to become life-threatening.

Numerous studies have shown that for terminally ill patients who choose to die, deaths by [[terminal dehydration]] are generally peaceful and not associated with suffering, when supplemented with adequate pain medication.<ref>{{cite journal |author=Printz LA |title=Terminal dehydration, a compassionate treatment |journal=Archives of Internal Medicine |volume=152 |issue=4 |pages=697–700 |year=1992 |month=April |pmid=1373053 |doi=10.1001/archinte.152.4.697 |url=http://archinte.ama-assn.org/cgi/pmidlookup?view=long&pmid=1373053}}</ref><ref>{{cite journal |author=Sullivan RJ |title=Accepting death without artificial nutrition or hydration |journal=Journal of General Internal Medicine |volume=8 |issue=4 |pages=220–4 |year=1993 |month=April |pmid=8515334 |doi=10.1007/BF02599271 |url=}}</ref>

== Differential diagnosis ==
In humans, dehydration can be caused by a wide range of diseases and states that impair
water [[homeostasis]] in the body. These include:

* External or [[stress (medicine)|stress]]-related causes
** Prolonged physical activity with [[sweating]] without consuming adequate water, especially in a hot and/or dry environment
** Prolonged exposure to dry air, e.g., in high-flying airplanes (5%–12% relative humidity)
** [[Blood loss]] or [[hypotension]] due to [[physical trauma]]
** [[Diarrhea]]
** [[Hyperthermia]]
** [[shock (circulatory)|Shock]] (hypovolemic)
** [[Vomit]]ing
** [[Burn (injury)|Burns]]
** [[Lacrimation]]
** Use of [[methamphetamine]], [[amphetamine]], [[caffeine]] and other stimulants
** Excessive consumption of [[alcoholic beverages]]

* [[Infectious diseases]]
** [[Cholera]]
** [[Gastroenteritis]]
** [[Shigellosis]]
** [[Yellow fever]]

* [[Malnutrition]]
** [[Electrolyte disturbance]]
*** [[Hypernatremia]] (also caused by dehydration)
*** [[Hyponatremia]], especially from restricted [[sodium chloride|salt]] [[Dieting|diet]]s
** [[Fasting]]
** 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 (2.2 lb)).<ref>[http://www.heartspring.net/symptoms_of_dehydration.html Dehydration Symptoms - Benefits of Drinking Water - Signs of Fluid Imbalance<!-- Bot generated title -->]</ref>
** [[Patient refusal of nutrition and hydration]]
** Inability to swallow (obstruction of the oesophagus)

Other causes of obligate water loss
* Severe [[hyperglycemia]], especially in [[diabetes mellitus]]
** [[Glycosuria]]
**[[Uremia]]
* [[Diabetes insipidus]]
* Acute emergency dehydration event
* [[Foodborne illness]]

== Prevention==

Dehydration is best avoided by [[drinking]] sufficient [[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 some water frequently).  

For routine activities in which a person is not perspiring to any large degree, drinking when one is thirsty is sufficient to maintain hydration.  However, during exercise, relying on thirst alone may be insufficient to prevent dehydration from occurring.  This is particularly true in hot environments or for those older than 65.  For an exercise session, an accurate determination of how much fluid is necessary to consume during the workout can be made by performing appropriate weight measurements before and after a typical exercise session, to determine how much fluid is lost during the workout.<ref>{{Cite web|url=http://www.webmd.com/balance/features/water-water-everywhere|title=Water, Water, Everywhere|publisher=WebMD}}</ref><ref>{{Cite web|url=http://health.msn.com/blogs/healthy-diet-fit-body-post.aspx?post=1188190|title=Metabolism Myth #5|publisher=MSN Health|author=Dr. Mark Dedomenico}}</ref><ref>{{Cite web|url=http://journals.lww.com/acsm-msse/Fulltext/2007/02000/Exercise_and_Fluid_Replacement.22.aspx|title=Exercise and Fluid Replacement|publisher=American College of Sports Medicine}}</ref><ref>{{Cite web|url=http://www.cbsnews.com/stories/2008/04/02/eveningnews/main3991145.shtml|title=Busting The 8-Glasses-A-Day Myth|publisher=CBS|author=Nancy Cordes}}</ref><ref>{{Cite web|url=http://dms.dartmouth.edu/news/2002_h2/08aug2002_water.shtml|title="Drink at Least 8 Glasses of Water a Day" - Really?|publisher=Dartmouth Medical School}}</ref>

Drinking water beyond the needs of the body entails little risk when done in moderation, since the kidneys will efficiently remove any excess water through the urine with a large margin of safety.

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.{{Fact|date=November 2008}} This can be through the lungs as [[water vapor]] (about 350ml), through the skin by [[perspiration]] (100ml) and by diffusion through the skin (350ml), or through the [[kidney]]s as [[urine]] (1000-2000ml, about 900ml of which is obligatory water excretion that gets rid of solutes). Some water (about 150-200ml, in the absence of [[diarrhea]]) is also lost through the [[bowel]]s.<ref>{{Cite document|url=http://www.sparknotes.com/health/minerals/major/section1.html|title=Major Minerals|publisher=SparkNotes|postscript=<!--None-->}}</ref> 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 either pre-hydrate<ref>{{Cite web|url=http://journals.lww.com/acsm-msse/Fulltext/2007/02000/Exercise_and_Fluid_Replacement.22.aspx|title=Exercise and Fluid Replacement|publisher=American College of Sports Medicine}}</ref> or find ways to reduce perspiration (through rest, a move to a cooler environment, etc.)

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.

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 [[Tonicity#Hypertonicity|hypertonic]] or [[Tonicity#Hypotonicity|hypotonic]] with respect to perspiration may have grave consequences ([[hyponatremia]] or [[hypernatremia]], principally) as the total volume of water turnover increases.

If water is being lost through mechanisms such as [[vomiting]] or [[diarrhea]], an imbalance can develop very quickly into a medical emergency. 

During sports events such as [[marathon]]s, athletes take frequent [[water stop (sports)|water stop]]s and [[water break]]s to avoid dehydration.

== Treatment ==
[[Image:Cholera rehydration nurses.jpg|right|thumb|250px|Nurses encourage a patient to drink an oral rehydration solution to improve dehydration he acquired from [[cholera]].]]

The treatment for minor dehydration often considered the most effective is drinking water and stopping fluid loss. Plain water restores only the volume of the blood plasma, inhibiting the thirst mechanism before solute levels can be replenished.<ref>"Formulating carbohydrate-electrolyte drinks for optimal efficacy." Murray, R. & Stofan, J. (2001).</ref> Solid foods can contribute to fluid loss from vomiting and diarrhea. <ref>"Healthwise Handbook," Healthwise, Inc. 1999</ref>

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 [[fluid replacement]] by [[intravenous therapy]]). As oral rehydration is less painful, less invasive, less expensive, and easier to provide, it is the treatment of choice for mild dehydration. Solutions used for intravenous rehydration must be [[Tonicity#Isotonicity|isotonic]] or [[Tonicity#Hypotonicity|hypotonic]].  Pure water injected into the veins will cause [[lysis]] of [[erythrocytes]].  

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]].

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.

Some research indicates that artificial hydration to alleviate symptoms of dry mouth and thirst in the dying patient may be futile.<ref>{{Cite document|title=Dehydration and the dying patient|author=JE Ellershaw, JM Sutcliffe, CM Saunders|publisher=Journal of pain and symptom|date=1995|url=http://linkinghub.elsevier.com/retrieve/pii/0885392494001233|postscript=<!--None-->}}</ref>

== References ==

* [[Ira Byock|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)

== Notes ==
{{reflist|2}}

== External links ==
{{wiktionary}}
* [http://www.water.org.uk/home/water-for-health/medical-facts/adults Water requirements in adults]
* [http://www.nlm.nih.gov/medlineplus/ency/article/000982.htm#visualContent Definition of dehydration by the U.S. National Institutes of Health's MedlinePlus medical encyclopedia]
* [http://rehydrate.org/index.html Rehydration Project at rehydrate.org]

{{Fluid, electrolyte, acid base metabolic pathology}}

[[Category:Causes of death]]
[[Category:Electrolyte disturbances]]
[[Category:Nutrition]]
[[Category:Symptoms]]

[[bg:Дехидратация]]
[[ca:Deshidratació]]
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[[es:Deshidratación]]
[[fr:Déshydratation]]
[[ko:탈수]]
[[hi:शरीर का निर्जलीकरण]]
[[id:Dehidrasi]]
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[[it:Disidratazione]]
[[he:התייבשות]]
[[kn:ನಿರ್ಜಲೀಕರಣ]]
[[lt:Organizmo dehidratacija]]
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[[nl:Dehydratie (geneeskunde)]]
[[ja:脱水 (医療)]]
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[[pl:Odwodnienie]]
[[pt:Desidratação]]
[[ru:Дегидратация (синдром)]]
[[simple:Dehydration]]
[[sk:Odvodnenie (choroba)]]
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[[ta:நீர்ப்போக்கு]]
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[[uk:Зневоднення організму]]
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[[Category:2Fix]]