That's not true. What are you basing that statement on? Once a patient is no longer able to make decisions, there is somebody else designated either in writing or by default secondary to relationship to the patient who gets to make decisions on behalf of the patient.
As written above, legally that is not quite true. If a relative has a
power of attorney then they are in the eyes of the law the exact equivalent of the patient and can do whatever they want without regard to the patient's previous wishes. However, in the absence of a power of attorney (or court appointed guardian) then a
healthcare surrogate is recognized. This is usually the
next-of-kin. The key difference between the two is that the "healthcare surrogate" is
legally obligated to follow the patient's expressed or implied wishes. If the patient has previously expressed that she wants to get her money's worth and wants everything done under the sun to keep her alive, then the
healthcare surrogate cannot legally say "pull the plug." (But the person named as the
attorney-in-fact can.) In the same way, if these types of wishes are necessarily implied from established religious beliefs (e.g., Jehovah's Witness, Catholic, Islam, etc.) then they have the same effect binding the actions of the
surrogate, but not the actions of the
attorney-in-fact.
In practice it can be a bit messier. If someone has a healthcare power-of-attorney then it is pretty simple; whatever they say goes. End of discussion. If the
surrogate and all the rest of the family stand together and lie about the patients desires, then you have no basis to contradict them, even though
they are acting illegally. But where it gets to be a real mess is if the
surrogate and the rest of the family and friends disagree. Because again, the
surrogate is only allowed to make those decisions that are consistent with a patient's previously expressed or implied wishes.
Advertisement: This is the reason why it is important to have an actual "Healthcare Power of Attorney" and appoint someone who will actually do what you want. (If you care about these things.)
The standard disclaimer: Every state has different laws. Know the law and regulations in the state where you practice. The fact you knew them at your last job or where you did your residency will not be a defense.