Siman 370

One whose neck is broken along with most of the flesh, and an old man even without most of the flesh (Shach), and similarly one who was torn from his back like a fish, even if he is still alive – he is considered as dead and conveys tumah. But if he was torn from his front – he does not convey tumah while he is alive. And if he was made into a gistera, where he was cut across his width at the neck or at the spine until its cavity, or if he was divided into two – he conveys tumah even if he is alive (ibid.). But the gosses, whether a gosses at the hands of man or at the hands of Heaven (it appears to me), and one whose two simanim, the trachea and the esophagus, were slaughtered, or one who is wounded with many wounds – they do not convey tumah until their soul departs. And there is room to doubt when one was hung by his neck and is still alive, if he is considered as dead. And it appears that he is not considered as dead, for if they were to untie him, it is possible to restore him to life.

Our teacher, the Beit Yosef, wrote: Nevertheless, it is forbidden for a kohen to enter a house in which there is a goses. Thus far his words. Our teacher, the Rema, wrote regarding this: And there are those who permit it, and it is good to be stringent. Thus far his words. For there is a dispute regarding this in Nazir (Nazir 43a), as there are those who expound "to profane himself" that one who enters to a goses, even though he does not become tamei until he dies, nevertheless profanes his priesthood. And there are those who disagree in the Gemara there. Most of the poskim ruled for prohibition, and so the Acharonim (Bach and Shach) agreed. And they disagreed with our teacher, the Rema, who wrote "it is good to be stringent," for by the letter of the law it is forbidden. In our times, the kohanim are careful regarding this and exit the house of the goses, and may their strength be firm for they sanctify the priesthood. However, if the kohen is sleeping—there is no need to awaken him from his sleep before he dies (Shach, subsection 4). And when the kohen is a doctor—it is permitted for him to enter to the goses to see if perhaps he can provide him a cure, for pikuach nefashot overrides everything. And if he dies—he shall flee from there. (And those kohanim who are doctors and cast off the yoke, who attend to the dead, and we are forced to call them according to the laws of the kingdom—the sin is not upon us, as the Chatam Sofer wrote in siman 338, and the Pitchei Teshuva cited him, see there.)