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Dehydration |
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In humans, dehydration can be caused by a wide range of diseases and states that impair water homeostasis in the body. These include:
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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
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Infectious diseases
- Cholera
- Gastroenteritis
- Shigellosis
- Yellow fever
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Malnutrition
- Electrolyte disturbance
- 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.)
- Patient refusal of nutrition and hydration
- Other causes of obligate water loss
- Severe hyperglycemia, especially in Diabetes mellitus
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Symptoms |
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 30%, 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.
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Treatment |
The 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.
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 an average adult can drink up to 0.2 liters of seawater per day before the kidneys start to fail.
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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