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Removal of water from any substance.
(organic chemistry)
An elimination reaction in which a molecule loses both a hydroxyl group (OH) and a hydrogen atom (H) that was bonded to an adjacent carbon.



splitting off of water from organic or inorganic compounds. Dehydration can be achieved thermally (mostly in the presence of catalysts) or chemically by the action of dehydrating agents (water-binding substances). The formation of ethylene from ethyl alcohol is an example of dehydration performed by passing ethyl alcohol through a tube containing aluminum oxide (catalyst) at 300°–400°C or by heating it with concentrated sulfuric acid (dehydrating agent) to 170°C:

CH3 —CH2OH → CH2 ═CH2 + H2O

The formation of ethylene is an example of intramolecular dehydration. However, heating the excess of ethyl alcohol with sulfuric acid to 140°C leads mainly to intermolecular dehydration with the resulting formation of diethyl ether:

CH3CH2 —O—H + H—O—CH2CH3 → CH3CH2 —O—CH2CH3 + H2O

Intramolecular dehydration of acetic acid CH3COOH yields ketene CH2=C=O, whereas the intermolecular dehydration of acetic acid yields acetic anhydride (CH3CO)2O. Dehydration of the amides CH3CONH2 yields nitriles CH3C≡N. Formation of nitrogen pentoxide from nitric acid in the presence of phosphorus pentoxide is an example of the dehydration of an inorganic substance:

Dehydration also includes the processes leading to the removal of water of crystallization from crystal hydrates and the removal of water bound by adsorption forces. Dehydration is the opposite of hydration.




loss of water by an organism to a point below the physiological norm. Animals die when they lose 20–25 percent of their body water, and disorders arise when the water loss reaches 10 percent. Dehydration may develop as a result of excessive water loss (repeated vomiting, diarrhea, excessive perspiration, extensive burns) or restriction of water intake.

Excessive water loss leads to hypo-osmolar dehydration, a condition in which the body loses a significant quantity of electrolytes along with the excreted fluids, the osmotic pressure in the cells is higher than in the interstices of tissues, and fluid enters the cells. When the water intake is restricted, the loss of fluid substantially exceeds the loss of electrolytes. This leads to hyperosmolar dehydration, a condition in which the osmotic pressure in the interstices of tissues increases and water passes from the cells to the extracellular space, as a result of which the cells become dehydrated and die.

Dehydration is accompanied by agonizing thirst, which is more difficult to endure than the hunger caused by deprivation of food. The secretion of all digestive glands is reduced, the blood thickens, and the blood viscosity increases. The changes in the blood lead to serious disorders of blood circulation and to disruption of renal function. Acute dehydration may lead to mental disorders, collapse, and sometimes death. Dehydration develops considerably more rapidly in children than in adults, since in children, especially infants, the amount of water excreted through the kidneys, skin, and lungs per unit of body surface is far greater than in adults. In pathological conditions causing hypo-osmolar dehydration, thirst should be quenched by drinking salted water to compensate not only for the water loss but the loss of electrolytes as well. Treatment consists in removing the primary cause of dehydration.



The removal of water vapor from air by the use of absorbing or adsorbing materials.
References in periodicals archive ?
To compare the effectiveness of using 5% dextrose for priming, reinfusion of the extracorporeal circuit and treatment of intravascular volume depletion symptoms against 0.
States of impaired water excretion Hypovolemic States * Volume depletion * Diuretics Euvolemic States * Postoperative state * Cortisol deficiency * SIADH * Pain * Hypothyroidism * Nausea Hypervolemic States * CHF * Cirrhosis * Nephrosis Fig.
or those who are aged 75 years and older, because these groups of patients were at higher risk of adverse reactions related to volume depletion in the studies.
Risk factors for amphotericin B-induced renal toxicity include volume depletion, pre-existing renal impairment, use of concomitant nephrotoxins, and high single and cumulative doses.
The studies examined the effects of these various intravenous solutions on relative blood volume, blood pressure and the relief of symptoms of volume depletion in people receiving haemodialysis treatment.
Volume depletion is more likely in endurance athletes who are exposed to prolonged exertion, such as marathon runners.
These patients have often experienced volume depletion, a drug nephrotoxicity or post-renal obstruction as the cause of AKI.
Hematocrit monitoring, a standard feature on new Aquapheresis devices and available as an optional upgrade to existing systems, automatically limits the fluid removal rate to help prevent excessive volume depletion due to high fluid removal rates and extended treatment times.
Other factors leading to ARF included volume depletion in 19 (20%) cardio renal in 13 (13.
It is not recommended for patients with moderate renal impairment, and the 5-mg dose is recommended for people at risk for volume depletion related to a coexisting condition.
For many (Amato, Hlebovy, King & Salai, 2008; Daugirdas, 2007), the "ideal" dry weight, sometimes referred by clinicians as "target weight" (Twardowski, 2009), is the weight the clinicians hope a patient will be at the end of each HD session, without suffering any of the intradialytic complications associated with intravascular volume depletion.
Likewise, an elevation in heart rate coupled with a low blood pressure may signal volume depletion (McCance & Huether, 1998).