Physicians may withdraw or withhold aggressive life-sustaining treatment under which condition?

There are a few scenarios that a physician may withdraw or withhold aggressive life sustaining treatment. First and most absolute is that when a patient requests that he or she wants the treatment to be withheld or withdrawn. Another scenario is when the healthcare team decides that the patient already is not benefitting (and actually becoming worse) with treatment. This will reflect the bioethical principle of double effect as the physician will decide whether the treatment does more harm than good.