“…sentience may go unnoticed for years, as was the case with Martin Pistorious [1] … Because brain death can be misdiagnosed [2], and because we have little understanding of the necessary and sufficient causes for consciousness and therefore cannot be certain of when someone might be in pain, some experts have called for the use of anesthesia [3] for organ donation procedures.”
Read more:
https://slate.com/technology/2016/04/the-challenge-of-determining-whether-an-a-i-is-sentient.html
[1] https://www.ted.com/talks/martin_pistorius_how_my_mind_came_back_to_life_and_no_one_knew?language=en
[2] https://www.nytimes.com/2012/04/01/books/review/the-undead-by-dick-teresi.html?_r=0
[3] https://onlinelibrary.wiley.com/doi/full/10.1046/j.1365-2044.2000.055002105.x