Also called "Power Red" by the American Red Cross. It is a procedure in which they take twice as much blood from you per donation, but return fluid to your body after each batch via sending it back up the tube to your veins. It is more efficient for the donator, as the preparation is the same whether you donate one pint or two: travel to the donation spot, getting your blood and blood pressure checked, filling out the forms, waiting your turn. The donation time is twice as long, but that is usually the short part anyway. I have long preferred it for this reason.
Well, never again. Today it went all wrong and the return fluids didn't go into the veins but into the surrounding tissue, so my upper arm is swollen enough that I will have to eat with my left hand. I can do most other things, gingerly. I kick myself, because I should have mentioned it immediately when it started to burn as soon as the fluid return started, which I knew from experience was not usual. But I just figured "Well, some times hurt more than others in a lot of things. Natural variation." Nope.