They can't, legally. The charade is that the patient chose to starve to death, by saying "no extraordinary medical procedure." That term of art includes feeding tube.
Succinct. What's scary to me in all of this is that "extraordinary medical procedures" and being kept alive by "artificial means" now includes food and water. We should be concerned that the judiciary considers us all to be alive by "artificial means," and that someone with "custody" of us on paper can decide to starve us to death.