血液是维持生命活动的重要物质，血液是在心脏和血管腔内循环流动的一种组织，成年人血容量约占体重的8％，出血是创伤后合并中主要之一。
Blood is an important material to maintain life activities. Blood is a kind of tissue circulating in the heart and vascular lumen. The adult blood volume accounts for about 8% of body weight. Bleeding is one of the main complications after trauma.
失血量的判断
Determination of blood loss
如失血量超过全身血容量的20%（约800毫升）以上时可出现轻度休克症状：伤员口渴、面色苍白、出冷汗脉搏快而弱、可达每分钟100次以上。
If the blood loss is more than 20% (about 800 ml) of the whole body blood volume, mild shock symptoms may occur: the wounded are thirsty, pale, sweating, and the pulse is fast and weak, reaching more than 100 times per minute.
如出血量为总血量的20％-40％（800～1600ml）时，可能会出现中度休克症状：呼吸急促、烦躁不安、脉搏可达每分钟100次以上。
If the amount of bleeding is 20% - 40% (800-1600ml) of the total blood volume, moderate shock symptoms may occur: shortness of breath, irritability, pulse can reach more than 100 times per minute.
如出血量达总血量的40％（1600ml）以上时可能出现重度休克症状：伤员表情淡漠、脉搏细弱或摸不到，血压测不清随时可能危及生命。
If the amount of bleeding is more than 40% (1600ml) of the total blood volume, severe shock symptoms may occur: the wounded's expression is indifferent, the pulse is weak or can not be touched, the blood pressure can not be measured clearly, and it may be life-threatening at any time.
因此，止血是抢救出血伤员的一项重要措施，它对挽救伤员生命具有特殊意义。
Therefore, hemostasis is an important measure to rescue the bleeding wounded, which has special significance to save the lives of the wounded.