Ideally, those decisions are made by the patient before the situation becomes critical. I know that doesn’t always happen and in that case the decisions would be made by the patient’s next of kin and the doctors that are treating the patient.
In the case of a DNR, that would be filled out and signed by the patient or the patient’s proxy and their primary physician in advance. This form basically states that the patient refuses treatment if they experience cardiac or respiratory failure: i.e. external compression, defibrillation and intubation.
In the absence of a DNR, resuscitation is attempted until either the patient stabilizes or it becomes clear that the patient will not be revived. That is typically a judgement call on the part of the attending physician.
At any time, a patient has the right to “informed consent”. You can freely give or withhold consent to any medical proceedure, medication, etc. And that means that a person has the right to have all treatments stopped at any time. For example, if a patient were in renal failure and had started dialysis treatments, but later decided s/he didn’t want to go through that anymore, s/he could refuse dialysis. Or if a patient were on a ventilator and didn’t want to live like that, s/he could ask for the vent to be removed. Of course, that only deals with patients that are cognizant and lucid.
If a patient is unable to give or withhold consent, normally the next of kin (wife, husband, parent, guardian) would make those decisions based on what the patient’s wishes would be. Withholding treatment or stopping treatment based on the patient’s wishes and/or maximum medical benefit is called Passive Euthanasia. It’s a large part of what Hospice does. All curative treatments are halted and palliative treatments are the main focus.
Assisted suicide requires that the patient be lucid and able to participate in their own medical care. Bascially, a physician/care provider gives the patient the means and instructions on how to die quickly and painlessly. In the US, I think that this is only legal in Oregon.
Active euthanasia requires someone else to make the decision to actively end the patient’s life without the patient being able to participate in the decision. I am of two minds on the issue. While I do see where active euthanasia could lead to abuses, I can’t understand why we can’t offer a kindness to our family members that we afford to our pets.
Since I live in Florida, I really need to get off my butt and get an Advanced Medical Directive and a Durable Medical Power of Attorney. That way, my wishes are spelled out long before I would be in a critical medical situation.