Death Definition

Igros Moshe (YD III #132) The definition of when a person is dead is stated explicitly in the gemora (Yoma 85a) in the case where a person is buried under a pile of rubble. It says he can be dug out even on Shabbos and then his nostrils are examined to determine if he is still breathing. Rambam and Shulchan Aruch rule that  if breathing is not detected he is considered dead. Thus we determine death by the absence of breathing. Even if the breathing is very slight he is considered alive. This can readily be determined with the aid of a feather placed near the nostrils. If the feather or a small piece of paper doesn’t move at all, he is presumed dead. Nevertheless he should be examined a number of times as I have explained previously to ensure he hasn’t just fainted because it is impossible to live without breathing. This test is valid only if the person is under constant watching. However since this is not realistic and it is possible he regained his strength a bit and was able to briefly get a few weak breathes it is impossible to properly determine death except by repeated testing. If these tests reveal there is no breathing at all than that is a sign the person is dead. This is more fully discussed by the Chasam Sofer. This is also relevant with the typical sick person who is close to dying, but is not dependent on a respirator. However there are many sick people who can not breathe without a respirator. Thus it is possible with a respirator to continue breathing even after death and these people are not considered alive.  If it is not clear that he is alive from other indicators e.,g. he doesn’t respond even if stabbed with a needle such as being in a state known as a coma. Then as long as the respirator is working it is prohibited to remove it from his mouth because he might be alive and by the removal he is being killed. However when the respirator stops working for example when the oxygen tanks are depleted, it is not required to put him back on the respirator when it starts working for a period of 15 minutes. If he is no longer alive as seen by the absence of breathing then it means he has died. IKn contrast if he is living as can be seen from the fact that he is breathing even without the respirator even if it is with difficulty and interruptions then he should be returned to the respirator immediately. This should be done a number of times until his condition improves or it is apparent that he can’t breathe on his own  and is dead. 

Igros Moshe (YD II #146) This that doctors say that the sign of of whether a person is alive or dead is in the brain In other words if according to their evaluation of a person if his brain is not working properly then he is considered that he is dead even though he is still breathing. You discuss this at length and try to refute this claim. You also say that the brain does not mean the brain stem at the top of the spine which you claim is irrelevant to this issue. I don’t understand your point. Since you are referring to the brain stem at the top of the spine in your discussion of the gemora in Chullin while the doctors are referring to the brain in the head. Furthermore the gemora is describing a case of where the brain stem is detached while the brain itself remains intact and healthy. If in fact the brain decomposes the animal is a treifa. Similarly if the brain dissolves and flows like water. Even though in general the status of treifa is because eventually the brain cover will be perforated, nevertheless the status of treifa occurs for other conditions both the actual brain and the brain stem. Thus it is possible to say like the doctors if the damage prevents the body from functioning properly it means death. Nevertheless it is certainly true that the brain stopping from  working is not what we define as death since as long as there is breathing he is considered alive. It just means that when the brain stops working it will lead to death which is defined as the cessation of breathing. It is possible that since such a person is still alive and that there are known or yet to be discovered medicines that will restore the function of the brain. It is also possible in this case to pray to G-d to cure him. Thus he has the status of a seriously ill person whose life is in danger but he is not considered dead. If he were dead it would be prohibited to pray for him since it is considered a meaningless and worthless prayer. It is also obvious that anyone who killed such a person is considered a murderer and is subject to the death penalty. All this is because there is no mention in the classic sources of the gemora and poskim that the brain status determines whether the person is considered alive. It is not relevant to claim that nature has changed in this issue because even in Talmudic times the brain functioned then as it does now and all of man’s functioning depended on it. Nevertheless it was not considered that the person was considered dead with the cessation of functioning of the brain and so today we don’t either.