I've only been a RC for five years, but I have never heard of this before. It sort of makes sense theologically though. Since we don't know when someone is completely dead or at what point the soul departs from the body, it is better to baptize just in case rather than not baptize at all when there was a chance that the person was still alive. However, I'm not totally sure how often this measure would be necessary. I mean, if someone is desiring to become Catholic and they die before their baptism, they would be saved via baptism of desire. If someone is medically dead but they did not believe while they were alive, would baptism help such a person?