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dehydration
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Dehydration (hypohydration)
is the removal of water (hydro in ancient Greek) from an object. Medically, it
is a condition in which the body contains an insufficient volume of water for
normal functioning.
Medical causes of dehydration in humans
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 without consuming adequate water, especially in a
hot and/or humid environment
Prolonged exposure to dry air, e.g., in high-flying airplanes (5-15% r.h.)
Survival situations, especially desert survival conditions
Blood loss or hypotension due to physical trauma
Diarrhea
Hyperthermia
Shock (hypovolemic)
Vomiting
Burns
Lacrimation
Infectious diseases
Cholera
Gastroenteritis
Shigellosis
Yellow fever
Malnutrition
Electrolyte imbalance
Hypernatremia (also caused by dehydration)
Hyponatremia, especially from restricted salt diets
Consumption of alcohol, caffeine or other diuretic substances.
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, or 2.2 lb.)[1]
Patient refusal of nutrition and hydration
Other causes of obligate water loss
Severe hyperglycemia, especially in Diabetes mellitus
Glycosuria
Symptoms and prognosis
Symptoms may include headaches 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, 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 50%,[citation needed]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, lack of tears when crying, headache, dry
mouth, and dizziness when standing due to orthostatic hypotension.
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. 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, vision may dim, urination will be greatly reduced and may become
painful, and delirium may begin. Losses greater than 15% are usually fatal. [2]
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Treatment
Nurses encouraging this patient to drink an Oral Rehydration Solution to improve
dehydration he acquired from cholera.
Courtesy:Centers for Disease Control and PreventionThe best treatment for minor
dehydration is drinking water and stopping fluid loss. 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.[3]
In more severe cases, correction of a dehydrated state is accomplished by the
replenishment of necessary water and electrolytes (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 cells to dehydrate and
the kidneys to overload and shut down but it has been calculated that average
adult can drink up to 0.2 liters of seawater per day before the kidneys start to
fail.[citation needed]
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.
Avoiding dehydration
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. A person's body, during an average day in a
temperate climate such as the United Kingdom, loses approximately 2.5 liters of
water. This can be through the lungs as water vapor, through the skin as sweat,
or through the kidneys as urine. Some water (a less significant amount, in the
absence of diarrhea) is also lost through the bowels. 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.). 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 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 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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