Logically, there may be little difference between discontinuing a machine that maintains the patient's breathing and discontinuing artificial nutrition and hydration. However, discontinuing artificial nutrition results in death by starvation and thirst over a period of days or weeks, as contrasted with the almost immediate death produced by discontinuing a respirator. The increased length of time that it would take for the patient to die from starvation and dehydration caused by the withdrawal of artificial feeding has influenced the opinion of some judges. The emotional ramifications of denying food and water to a seriously ill person have also affected judicial opinions and legislation. Clearly, this is a question about which there is no consensus among courts and legislatures.
Michelle L. Oxman, Encouragement of Empathy: Just Decision making for Incompetent Terminal Patients, 3 J.L. & Health 189 (1988-1989)