Oxygen is given because the surgical trauma is relatively large, and I am afraid that your mother’s oxygen saturation will be low, which may lead to a series of problems such as brain damage and tissue necrosis. In fact, as long as the monitoring is good, there is no need to inject oxygen, but the problem is that there are not so many nurses to watch at your mother's bedside, so oxygen is administered, which can increase the oxygen saturation and facilitate recovery.
In the case of blood transfusion, there are two possibilities. One is that there is indeed a lot of bleeding during the operation, after all, the spine is a hematopoietic organ; the other is excessive medical treatment.