This is a tough one and totally dependent on the circumstances and the recent mindset of the persons.
For example recently while visiting my Grandmother she had a heart attack right in front of me. She has always stated not to "save" her, she has strict DNR papers. She was ready to go when the LORD called. I reacted on my own accord and called EMS, kept her lucid and talking. I was 'slow' on getting to the hospital with all the calls alerting family and gathering her meds and DNR papers. The hospital stabilized her enough to have her transported to a Heart Hospital before I got there. Before I reached the other hospital 100 miles away she had already been to surgery and stented.
The ending: She is happy to be alive! She adjusted her thinking to accept that the Lord was preparing her for greater things and put me there to make sure his plan was carried out. The DNR is now only for vegetative states.
My mom still is clinging to the blood thing, she knows I will disregard the matter but keeps me as her POA. Reason: It won't be her fault she said no, but I decided to overrule. Life is meant to be held precious and if a JW is given blood because of POA overriding they are not guilty or automatically DAd. I will happily play the "bad guy"