Dehydration

Dehydration is a condition caused by an insufficient amount of water in the body. Outside of hospitals, it's generally the result of lack of water, such as might occur when a person is stranded in an arid environment. However, it is not uncommon in hospitals with patients with several common conditions being at risk. The three main causes are:
*Inability to take in oral fluids, as is common with patients suffering from severe nausea or taking chemotherapy. The most common treatment is intravenous fluids.
*Excessive urination, as is common with sufferers of diabetes insipidus or certain hemorrhagic fevers. Usually, patients can be given intravenous fluids.
*Sweating from fever. Again, oral or intravenous fluids are necessary depending on the condition of the patient.
Water is not recommended for patients suffering from severe dehydration as they may suffer from water based edema in the digestive system as it tries to absorb the water. There are special electrolyte solutions for such situations which mix glucose and salts with the water to allow even absorption of the water.
Unconscious patients are usually given intravenous fluids to avoid dehydration. However, the urine production of these patients must be closely monitored to ensure that they have sufficient kidney function, otherwise edema will result and dialysis may be necessary.
Dehydration at Wikipedia
ru:Обезвоживание