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Dehydration
Classification and external resources
Nurses encourage a patient to drink an oral rehydration solution to reduce dehydration he acquired from cholera.
ICD-10	E86
ICD-9	276.5

In physiology and medicine, dehydration (hypohydration) is defined as the excessive loss of body fluid.^[1] It is literally the removal of water (Ancient Greek: ὕδωρ hýdōr) from an object; however, in physiological terms, it entails a deficiency of fluid within an organism. Dehydration of skin and mucous membranes can be called medical dryness.

There are three 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).^[2] 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 seizures, while the latter can lead to osmotic cerebral edema upon rapid rehydration.^[3]

Definition[link]

Hypovolemia is specifically a decrease in volume of blood plasma.^[4][5] Furthermore, hypovolemia defines water deficiency only in terms of volume rather than specifically water.

Signs and symptoms[link]

Symptoms may include headaches similar to what is experienced during a hangover, 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. Athletes may suffer a loss of performance of up to 30%^[6] and experience flushing, low endurance, rapid heart rates, elevated body temperatures, and rapid onset of fatigue.

Symptoms 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 insomnia. Other possible symptoms include cloudy urine and stinging during urination. Blood tests may show hyperalbuminemia. Mild dehydration also has been shown to negatively impact people’s moods. Experiments by the USDA's Agricultural Research Service has shown that dehydration is associated with confusion, fatigue, and negative moods.^[7] 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, seizures, sunken fontanel (soft spot) in infants, fainting, and sunken eyes.

The symptoms become increasingly severe with greater water loss. One's heart and respiration rates begin to increase to compensate for decreased 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 the elderly dying suddenly 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.

In studies of terminally ill patients who have chosen to die, it has been shown that deaths by terminal dehydration are generally peaceful, and are not associated with suffering when supplemented with adequate pain medication.^[8][9]

Differential diagnosis[link]

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-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 (hypovolemic)
  • Vomiting
  • Burns
  • Lacrimation
  • Use of methamphetamine, amphetamine 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 salt diets
  • 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)).^[10]
  • 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[link]

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.^{[11][12][13][14][15]}

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 litres of water.^{[citation needed]} 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 kidneys 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 bowels.^[16] In warm or humid weather or during heavy exertion, however, the water loss can increase by an order of magnitude or more^{[citation needed]} 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^[13] 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.^{[citation needed]}

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.

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 marathons, athletes take frequent water stops and water breaks to avoid dehydration. The claim that pure water without isotonic additives can prevent dehydration is questioned, however, and the European Food Safety Authority states that reduced body water content is only a symptom of dehydration and not what drinking water controls.^[17] Drinking water without replenishing electrolytes may instead lead to developing hypotonic dehydration.

Treatment[link]

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.^[18] Solid foods can contribute to fluid loss from vomiting and diarrhea.^[19]

In more severe cases, correction of a dehydrated state is accomplished by the replenishment of necessary water and electrolytes (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 isotonic or hypotonic. Pure water injected into the veins will cause the breakdown (lysis) of red blood cells (erythrocytes).

When fresh water is unavailable (e.g., at sea or in a desert), seawater, alcohol, and even urine will worsen the condition.

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.^[20]

See Also[link]

• Terminal dehydration

References[link]

• Ira R. Byock, M.D., "Patient Refusal of Nutrition and Hydration: Walking the Ever-Finer Line." American Journal Hospice & Palliative Care, pp. 8–13. (March/April 1995)

Notes[link]

External links[link]

Look up dehydration in Wiktionary, the free dictionary.

• Dehydration Causes and Symptoms
• Water requirements in adults
• Definition of dehydration by the U.S. National Institutes of Health's MedlinePlus medical encyclopedia
• Rehydration Project at rehydrate.org
• About dehydration
• Are you drinking enough?
• Skin Diseases Informations | SkinTurgor.com

This article has multiple issues. Please help improve it or discuss these issues on the talk page. This biography of a living person needs additional citations for verification. Tagged since July 2009. Its lead section may not adequately summarize its contents. Please consider expanding the lead to provide an accessible overview of the article's key points. Tagged since November 2009.

Raymond Paul "Ray" Mears (born 7 February 1964) is an English woodsman, instructor, author and TV presenter. His TV appearances cover bushcraft and survival techniques, and he is best known for the TV series Ray Mears' Bushcraft, Ray Mears' World of Survival, Extreme Survival, Survival with Ray Mears, Wild Britain with Ray Mears and Ray Mears Goes Walkabout.

Early life[link]

Mears grew up in Kenley, Greater London, and the North Downs, where he discovered a countryside abundant with wildlife. Educated at Reigate Grammar School, a co-educational independent school in Reigate, Surrey, he learned to track foxes in the forest at a young age. As a boy, he desired to sleep out on the trail, but unable to afford camping equipment, he resorted to setting up camp using what he could find in his surroundings.

Interests[link]

Mears's enthusiasm for his subject, combined with his broad knowledge of survival and the uses which may be made of plants, trees and other natural materials found in woodland, forest or desert, have made him a popular figure in TV broadcasting in the UK.^{[citation needed]} He has travelled extensively across the world for his TV series and has learned survival techniques from the indigenous peoples he has met. In his programmes he demonstrates his knowledge of the wild, how to find food from seeds, berries, roots and other growing things, and how to survive by constructing temporary shelters, fires and canoes from natural materials.

Mears has practiced Judo for many years. He once proudly on TV when challenged as a guest wrestled the then winner of a 6 player bushmans tournament. Mears emerged victorious after a strenuous and competitive match. The bush community were most impressed.

Mears is particularly interested in the survival of groups of resistance fighters and partisans for extended periods during the Second World War, such as the Norwegian heavy water plant saboteurs (see The Real Heroes of Telemark^[1]) and the Bielski brothers in Belarus (see Extreme Survival).

Personal life[link]

Mears met his partner, Rachel, in 1992 when she attended one of his five day survival courses. The couple lived in East Sussex with her two adult children, and married in 2005, after Rachel was diagnosed with breast cancer. Rachel died from cancer in 2006, aged 50, and her ashes are scattered in the Ashdown forest near their home.^[2]

While filming a documentary in Wyoming in 2005 Mears was involved in a serious accident. The helicopter in which he and his camera crew were travelling struck the ground during a steep low level turn, and broke apart, rolling to a stop. The fuel tank was ruptured in the accident, and escaping fuel covered Mears and the crew. No fire occurred, and Mears was able to escape the wreckage and assist in the rescue and first aid of one of the crew who was badly injured. Mears escaped uninjured.^[3]

Non-television work[link]

Mears started his bushcraft company aged 19. Mears' first book, The Survival Handbook, was published in 1990. Mears has continued to publish books, both standalone works, and as accompaniments to his TV series.

In September 2007, he was awarded an honorary doctorate from Oxford Brookes University, and in the same year he began to deliver public lectures across the United Kingdom on his experiences in front of and behind the lens.

In July 2010, Mears was asked by Northumbria Police to help them track fugitive killer Raoul Moat, after he fled his temporary tent-based shelter in the village of Rothbury.^[4]

Television[link]

Mears has made a number of series for BBC television, visiting various parts of the world and covering such topics as bushcraft and survival skills, the traditional culture of indigenous peoples, and the achievements of noted explorers.

In 2009 he was approached by ITV to present a planned revival of its long-running nature documentary series Survival.^[5] The resulting three-part series was rebranded Survival with Ray Mears and broadcast on ITV1 in 2010. Each episode followed Mears as he used his tracking skills to locate bears, wolves and leopards. In a Radio Times interview to promote the series, Mears complained of being typecast by the BBC.^[6] This series was followed by Wild Britain with Ray Mears, also broadcast by ITV.

Series[link]

• Wild Tracks (BBC, 1994)
• Tracks (BBC, 1994–97)
• Ray Mears' World of Survival (BBC, 1997–98, 2 seasons of 6 episodes each)
• Ray Mears' Country Tracks (BBC, 1998, 2002–03)
• The Essential Guide to Rocks (BBC Education, 1998)
• Ray Mears' Extreme Survival (BBC, 1999–2002, 3 seasons of 6 episodes each)
• Ray Mears' Adventure Special (BBC, 2001) – Mears takes Ewan McGregor into the Honduran jungle on the trail of the prehistoric people of the Mosquito Coast.
• Ray Mears' Real Heroes of Telemark (BBC, 2003)
• Ray Mears' Bushcraft (BBC, 2004–05, 2 seasons of 5 episodes each)
• Ray Mears' Wild Food (BBC, 2007, 5 episodes)
• Ray Mears Goes Walkabout (BBC, June 2008, 4 episodes)^[7] – Mears tours the Australian outback. An accompanying hardcover book was published in the UK by Hodder and Stoughton in March 2008. In the series Mears meets one of his heroes: Les Hiddins (aka "The Bush Tucker Man"). He also heads to the Kimberley region to meet the reputed aboriginal artist and bush guide Ju Ju Wilson.
• Ray Mears' Northern Wilderness (BBC Two, Autumn 2009, 6 episodes) – Mears follows in the footsteps of pioneers who opened up Canada, such as Samuel Hearne, John Rae and David Thompson.
• Survival with Ray Mears (ITV, Spring 2010, 3 episodes)
• Wild Britain with Ray Mears (ITV, Autumn 2010, 6 episodes) - To be followed in 2011 by extended 60 minute episodes with exclusive additional content to be broadcast on UKTV's natural history channel Eden.

Books[link]

• The Survival Handbook (1990)
• The Outdoor Survival Handbook (1992)
• Ray Mears' World of Survival (1997)
• Bushcraft (2002)
• Essential Bushcraft (2003)
• The Real Heroes of Telemark: The True Story of the Secret Mission to Stop Hitler's Atomic Bomb (2003)
• Ray Mears' Bushcraft Survival (2005)
• Wild Food by Ray Mears & Professor Gordon Hillman (2007)
• Ray Mears Goes Walkabout (2008)
• Vanishing World - A Life of Bushcraft (2008)
• Northern Wilderness (2009)

Quotations[link]

Quotations by Ray Mears include:

• "Bushcraft is what you carry in your mind and your muscles."
• "The great thing about bushcraft is that wherever you go, the skills go with you."
• "One of the great things about bushcraft is that skills you learn in your back garden can be used all over the world." ^[8]
• "Knowledge is the key to survival and the best thing about that is: it doesn't weigh anything."
• "You cannot underestimate the importance of preparation."
• "As far as I'm concerned, these people are just showmen." On Bear Grylls^[9]

See also[link]

• Les Hiddins
• Mors Kochanski
• Lofty Wiseman
• Richard Proenneke
• Les Stroud
• Bear Grylls
• Rüdiger Nehberg
• Bruce Parry
• Lars Monsen

References[link]

External links[link]

• Official website
• Ray Mears on Myspace
• Ray Mears at the Internet Movie Database
• Ray Mears Woodlore on Facebook
• Ray Mears Bushcraft's channel on YouTube
• Ray Mears' Survival shows on Dave (UKTV)
• Photographs of 2005 helicopter accident
• Wild Britain on itvWILD