Is hypovolemia different from dehydration

What is hypovolemia? Is it different from dehydration?

Hypovolemia is generally synonymous with ECF volume contraction. Physicians should distinguish between ECF volume contraction and dehydration. ECF volume contraction implies a loss of sodium and water. Dehydration implies a loss of water. For example, a loss of 1 L of fluid containing 150 mmol sodium will cause the ECF volume to fall by 1 L. Because the lost fluid is isotonic, plasma osmolality will not change. A loss of 1 L water, however, will cause much less ECF volume contraction. Water will be lost proportionately from all body fluid compartments. Because two-thirds of total body water is intracellular and one-third is extracellular, a loss of 1 L water will cause the ECF volume to fall by only 0.33 L. Plasma osmolality will rise. A loss of 1 L water is more properly called dehydration. Losses of water, then, are less likely to cause manifestations of ECF contraction than are losses of sodium and water ( Fig. 71.3 ). Losses of water, however, may cause manifestations of hypernatremia.


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