Guidance from the Catholic Church.
Pope Francis - "….it has also become possible nowadays to extend life by means that were inconceivable in the past. Surgery and other medical interventions have become ever more effective, but they are not always beneficial: they can sustain, or even replace, failing vital functions, but that is not the same as promoting health. Greater wisdom is called for today, because of the temptation to insist on treatments that have powerful effects on the body, yet at times do not serve the integral good of the person.” Message to European regional meeting, World Medical Association, November 7, 2017
"In principle, there is an obligation to provide patients with food and water, including medically assisted nutrition and hydration for those who cannot take food orally…The free and informed judgment made by a competent adult patient concerning the use or withdrawal of life-sustaining procedures should always be respected and normally complied with, unless it is contrary to Catholic moral teaching." ERD, 58 and 59, p 31 A.
For the dying patient - Medically assisted nutrition and hydration become morally optional when they cannot reasonably be expected to prolong life or when they would be “excessively burdensome for the patient or [would] cause significant physical discomfort, for example resulting from complications in the use of the means employed. For instance, as a patient draws close to inevitable death from an underlying progressive and fatal condition, certain measures to provide nutrient and hydration may become excessively burdensome and therefore not obligatory in light of their very limited ability to prolong life or provide comfort. ERD, 58, p 31 “...
[W]e should not assume that all or most decisions to withhold or withdraw medically assisted nutrition and hydration are attempts to cause death. To be sure, any patient will die if all nutrition and hydration are withheld. But sometimes other causes are at work—the patient may be imminently dying…from an already existing terminal condition.” Nutrition and Hydration: Moral and Pastoral Reflections, USCCB, 1992 B.
For the patient in a “persistent vegetative state” - This obligation [to provide food and water] extends to patients in chronic and presumably irreversible conditions (e.g., the “persistent vegetative state”) who can reasonably be expected to live indefinitely if given such care. ." ERD, 58, p 31
"In particular, I would want to emphasize that the administration of water and food, even when it is provided by artificial means, always represents a natural means of preserving life, not a medical intervention. Its use is therefore considered to be, according to the principle, proportionate, ordinary and as such, morally obligatory, in the degree to which and until it has been demonstrated to attain its own proper finality, which in this instance consists in providing nutrition to the patient and alleviating their suffering.” Pope John Paul II on Life-Sustaining Treatment and the Vegetative State (March 20, 2004)