Dehydration

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dehydration

[‚dē·hī′drā·shən]
(chemistry)
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.

Dehydration

 

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.

B. L. DIATKIN


Dehydration

 

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.

G. A. DROZDOVA

dehydration

The removal of water vapor from air by the use of absorbing or adsorbing materials.
References in periodicals archive ?
Yet, findings could be interpreted in that moderate and careful volume and substitution may be preferable over strict volume depletion in this highly febrile disease as it may not only improve cardiac output but also may have a beneficial effect on microcirculation, tissue perfusion and lactic acidosis.
Thiazide diuretic use may also predispose to the development of this condition by enhancing renal tubule calcium absorption and by promoting volume depletion and alkalosis.
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.
Isotonic crystalloid solutions are effective in the treatment of intravascular volume depletion due to fluid losses.
Pre-renal azotemia is the condition characterized by increased levels of BUN as can occur with volume depletion.
As the aging process is better understood, doctors have realised that facial volume depletion and migration causes facial ageing.
The landmark SAFE (Saline versus Albumin Fluid Evaluation) study went most of the way in answering the question of type of fluid for the treatment of intravascular volume depletion in critically ill patients (1).
VITAL SIGNS Top 10 Diagnoses for Discharge From Short-Stay Hospitals (in thousands) Heart disease 19,747 Hypertension 9,003 Diabetes 5,480 Psychoses 4,038 Mothers with deliveries 3,831 Anemias 3,439 Malignant neoplasms 2,558 Volume depletion 2,385 Uninary tract infection 2,230 Note: Based on 2005 data for all listed diagnoses.
9,10) The postoperative state is characterized by multiple stimuli for ADH release including pain, stress, nausea, vomiting, narcotic medications, and volume depletion.