The thing I have wondered about is the fact that blood transfusions don't increase oxygen carrying ability of the stored blood for a number of days, and if the blood has been stored for to long can even hamper oxygen release.
Here's a quote I found:
"Blood in cold storage contains glucose as a potential substrate for ATP production, but the glycolytic enzymes do not work well in the cold. Remember, DPG is produced as a byproduct of glycolysis. Thus, DPG levels decrease in refrigerated (stored) blood. Thus, if refrigerated whole blood is stored for too long, it becomes less efficient at O2 unloading, because it contains less DPG!
DPG decreases so much by the time the blood is 10 days old that the Hb affinity for O2 is actually increased such that less O2 is released from Hb which has been refrigerated for 10 days. For this reason, refrigerated blood is not normally stored beyond 21 days; if refrigerated blood older than 21 days is transfused, it picks up O2 at the lung but will not release the O2 at the tissues. Transfusion of blood older than 21 days actually impairs O2 transfer to the tissues. When older refrigerated blood is returned to the body, the levels of DPG present in the blood will gradually increase, but the initial decline in O2 carrying capacity following transfusion should be considered potentially dangerous. Blood which is to be used for planned autologous transfusions (planned surgeries, for example), should be frozen if it will not be used within a few weeks... and must be frozen if it is to be stored for 42 days or more. While improving cell freezing technologies (development of less toxic cryoprotectants) allows cells to be frozen indefinitely, frozen blood is generally used within 1 year, but is readily frozen for 10 years or more.
Remember, DPG levels are increased in people living at high elevations, such that the efficiency of O2 unloading from their Hb at the tissues is increased."
I wonder if this still applies to packed red blood cells. As it takes 24-48 hours for the transfused blood to reach full O2 carrying ability they would need to be timed right or it would seem that Hemopure or a similar product would be more useful.