People have been throwing a 2 1/2 liter measurement around but from all of the research I’ve done that’s… improbable. He’d be unlikely to survive. Granted those charts are aimed at average sized people with average physiologies and not Sam, but still. I’m going to go with a 2L measure - still significant enough to cause the reaction we’ve seen, not enough to require immediate aggressive intervention - until told otherwise.
My training is also in archaeology and accountancy - if blood is involved with either there’s probably a problem. (Not to say that it doesn’t happen, but…) If anyone who is in a more hard-science field wants to take a stab at this I’d be most grateful.
Thanks to a handy-dandy blood volume calculator and an estimation of 6’4” and 190 lbs (thanks, Google), Jared Padalecki has ~6.02 liters of blood, and that may be one of the creepiest sentences I have ever typed. You can lose about 40% of your total blood volume before you pass out - in Jared Padalecki’s/Sam’s case, that’s about 2.4 liters. That is absolute most he could lose under calm circumstances without going into shock and requiring a transfusion. For comparison purposes, that’s about five pints. Blood donations generally take only one pint.
However, he was tied to a chair and being bled out by vampires while his brother lay unconscious on the floor. I would give him no more than 1.5 L (3 pints) before shock set in, and if his heart rate was elevated (which is more than likely), he would probably need a transfusion by the time Den cut him loose because he was still bleeding.
I thought you might be one of the people to come up with the solution, although I didn’t want to put you on the spot! Thank you so much, both for the help and for the awesome blood volume calculator. Because that is just so incredibly helpful in so many ways.