A compelling argument can be made that blood that is poured out is a symbol not of life, but of death. We will not spend time developing this argument but want to acknowledge that it exists and is both plausible and compatible with our understanding of blood serving as a symbol of life when it is flowing through the body of a living creature. Although the Mosaic law will later prohibit the actual eating of blood, technically no such prohibition occurs here. Indeed, if an animal has been bled, it has to be dead. The provisions of the covenant were not absolute, exceptions were made.
Blood is used as a metaphor for life.
Its use is symbolic not literal. Additionally, the entire discussion of blood takes place in the context of killing, either animals or humans. This is an important point because blood transfusion does not involve killing. Quite to contrary, such blood is used for the purpose of preserving life. Clearly the blood of Jesus is greater since the Bible teaches that his shed blood was able to provide for the forgiveness of sin.