Hemodilution is the removal of one or more units of blood before a surgery, so that the blood can be put back into the body during or after the surgery. When the blood is collected before the surgery starts it is stored in blood collection bags. Then the blood volume is restored using volume expanders. Finally, the blood is returned to the patients body when major bleeding has ceased. Some view the procedures of hemodilution as a way to extend a patients circulatory system and in the process restore the volume of a patients blood. However, the blood does leave the natural circulatory system of a patient.