I'm so sorry that you're having to experience this.
I went through the same thing maybe 3 months ago when my mother had to have surgery in her abdominal area =. From the way the surgeon was describing the problem she was having, severe blood loss was very much guaranteed. He even said he wished my mother wasn't a JW(she's not baptized by the way) and would take blood. Even though she lost alot during the surgery, it was built back up to normal now.
Very scary situations are what these are. I hope that your father will end up alright and that you can remain strong during all of this.
R.F.