Or, consider the patient who is demented and is admitted with pneumonia from aspiration and who is DNR/DNI and is given supplemental oxygen. Does escalation of oxygen therapy to a non-rebreather mask from nasal cannula fly in the face of his DNR order? Does the administration of peripheral vasopressors for hypotension have the same result? Does DNR/DNI mean Do Not Respond/Do Not Intervene?
These are thorny issues indeed, and I do not presume to have the solutions to them. But I can offer some practical guidance, from experience.
Firstly, as documented in other posts, the fatalistic perspective "if it was meant to be, it shall be" can answer some of these dilemmas. I often tell patients' families that if we tread lightly and put aside our critical care armamentarium, we may often be surprised how resilient patients are as highlighted in the linked post. Beneficient neglect is often their salvation. So a compromised middle ground may be to give limited supplemental oxygen up to 6 liters nasal cannula. Why 6 liters? Because it keeps open options for moving the patient to a more forgiving place of care such as the floor, or home, or hospice. It may even allow them to "rally" if that was "meant to be."
Secondly, a trial of reduced care, such as extubation to 6 liters nasal cannula will allow us to observe how patients do and to integrate this information iteratively into the plan of care. If a patient is extubated to low flow oxygen and gets gradually better, we have actionable information, we can make plans contingent on this early course and trajectory. If, on the other hand, there is deterioration, we can very reasonably presume that escalating oxygen therapy to venturi mask then non-rebreather mask, and then, God forbid, BIPAP is not going to get us anywhere - the trajectory has manifested itself, and we are simply delaying the inevitable and fooling ourselves.
Thus, if the patient is moribund, we have few decisions to make. If they or their surrogates declare that they wish to tread lightly and "let him have a natural and dignified death," or "play the hand they were dealt" or "take it as it comes" we can withhold most life sustaining and death prolonging measures such as oxygen, fluids, antibiotics, and vasopressors, and allow him to have a dignified death as chronicled in this very nice piece in this week's NEJM.
But, if we are in the gray zone and ambivalence and indecision and perhaps guilt pervade, it seems to me to make sense to give a very limited trial of therapies that are not invasive and cumbersome such as peripheral vasopressors and low flow oxygen by nasal cannula as a limited trial to determine the trajectory. If the patient "rallies" we may decide to pursue this course and make disposition decisions contingent upon it. If they deteriorate, or remain static in a condition that is unacceptable to the patient and/or his surrogates, it seems reasonable to reorient ourselves to letting death take its natural course without intervening with dehumanized technology.