BLOOD TRANSFUSION

I don't know what you mean by "prime the blood".... you just prime the tubing with saline then start running the blood (slowly, according to protocol).

Close all the clamps before you begin. Spike the saline bag. Open the upper clamp and run the saline into the drip chamber until it covers the filter (not until it fills the chamber---it should be about 2/3 full or so). You can squeeze the chamber gently (don't crush the filter) until it is filled to the desired level.
Leaving the upper saline clamp open you should now open the lower clamp and fill the lower tubing completely with saline. Now close all the clamps again. Attach the set to the patient at this point and it will be all ready by the time your blood product arrives.
Spike the blood bag, open the upper blood line clamp and the lower main line clamp (leaving the saline bag clamped) and let the blood product drip into the chamber. The air in the blood line will go into the chamber, not into the main line.
Leave the saline bag clamped during and after priming with the blood or your blood will go up into the saline bag. Not pretty but it happens fairly frequently---we've all seen those pink bags of saline hanging next to a bag of packed cells.
Now run the blood.
I'm tired and apologize if I screwed this up---someone step in and please correct it if I did!