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Hypovolemia, also known as volume depletion or volume contraction, is a state of abnormally low extracellular fluid in the body. [1] This may be due to either a loss of both salt and water or a decrease in blood volume. [2] [3] Hypovolemia refers to the loss of extracellular fluid and should not be confused with dehydration. [4]
Class 3: Volume loss from 30% to 40% of total blood volume, from 1500 mL to 2000 mL. A significant drop in blood pressure and changes in mental status occur. [3] Heart rate and respiratory rate are significantly elevated (more than 120 BPM). Urine output declines. Capillary refill is delayed. [3] Class 4: Volume loss over 40% of total blood volume.
Intravascular volume depletion is divided into three types based on the blood sodium level: Isonatremic (normal blood sodium levels) Example: a child with diarrhea, because both water and sodium are lost in diarrhea.
Volume contraction is a decrease in the volume of body fluid, including the dissolved substances that maintain osmotic balance . The loss of the water component of body fluid is specifically termed dehydration .
The term "dehydration" has sometimes been used incorrectly as a proxy for the separate, related condition of hypovolemia, which specifically refers to a decrease in volume of blood plasma. [3] The two are regulated through independent mechanisms in humans; [ 3 ] the distinction is important in guiding treatment.
EABV can be reduced, therefore, by factors which reduce actual arterial blood volume (hemorrhage, dehydration), increase arterial vascular capacitance (cirrhosis, sepsis) or reduce cardiac output (congestive heart failure). EABV can be reduced in the setting of low, normal, or high actual blood volume.
Glucosuria causes a loss of hypotonic water and Na +, leading to a hypertonic state with signs of volume depletion, such as dry mucosa, hypotension, tachycardia, and decreased turgor of the skin. Use of some drugs, especially stimulants, may also increase blood glucose and thus increase urination. [citation needed].
The classic example of a dehydration reaction is the Fischer esterification, which involves treating a carboxylic acid with an alcohol to give an ester RCO 2 H + R′OH ⇌ RCO 2 R′ + H 2 O. Often such reactions require the presence of a dehydrating agent, i.e. a substance that reacts with water.