Life support, in the medical field, refers to a set of therapies for preserving a patient's life when essential body systems are not functioning sufficiently to sustain life unaided. Life support therapies utilize some combination of several techniques: feeding tubes, intravenous drips, total parenteral nutrition, mechanical respiration, heart/lung bypass, urinary catheterization and dialysis. The same techniques are also used for intensive care or in some cases during surgery, though life support is employed to stabilize a patient and is typically not sufficient to allow full recovery from their condition.
It has been proposed that the practice of artificially prolonging the life of an individual who will not recover to be unethical. Roman Catholic moral teachings, pronounced in 1993, suggest that the employment of artificial means is not necessary to fulfill the duty to respect life; however the term "artificial means" may vary in meaning between different schools of thought within and outside Catholicism. Most Catholic theologians however, divide the issue into "ordinary" and "extraordinary" means, and believe that it is an ethical imperative to continue the ordinary means, but ethically neutral to withhold the extraordinary means. They define ordinary means as things like feeding, and extraordinary means as things like artificial breathing. Also you could say that it is illegal in some states.