Hi Heretic,
I would ask your brother if he really believe doctors would use blood if it is so much more dangerous than bloodless surgery. With risk of being sued and problems getting insurance does he really believe that doctors do not do what is best for the patient? He is getting philosphical about the word "proven", because if a person is dead it is hard to "prove" 100% they would not be dead with blood. However, statistics indicate that there are many situations where a person will die without blood. When there is massive bleeding volume expanders do not have the oxygen carrying ability that only red blood cells provide. Without a transfusion in such situations the person will die.
The Bible does not forbid blood transfusions. At http://www.jwfacts.com/index_files/blooddoctrine.htm I have show why do not think it is wrong to even eat blood. At Acts it says blood and food sacrificed to idols are wrong, yet Paul clearly shows elsewhere that food sacrificed to idols is only wrong if it stumbles a brother.