血容量减少，亦称血容量过低、休克，指的是体内血量减少的状况。 它表现在体内血液体积收缩和脱盐上。

常见的血容量减少的原因有：

• 血液减少（例如内外出血或献血）
• 血浆减少（例如严重烧伤）
• 缺钠或血管内水分减少（例如腹泻、呕吐）
• 血管舒张（例如遭到致使神经紊乱的创伤、血管舒缩中枢抑制）

Hypovolemia (also hypovolaemia or oligemia) is a state of decreased blood volume; more specifically, decrease in volume of blood plasma. It is thus the intravascular component of volume contraction (or loss of blood volume due to things such as bleeding or dehydration), but, as it also is the most essential one, hypovolemia and volume contraction are sometimes used synonymously.