These statutes usually provide that withdrawing life-sustaining procedures or otherwise conforming to treatment decisions does not constitute homicide, assisted suicide or euthanasia. An advance directive doesn't have any effect as long a patient is able to speak for him- or herself. It comes into play when the patient becomes unconscious or is too sick or demented to make detailed choices about treatment. A patient may be competent to make some decisions but not all. An advance directive can be revoked if a patient changes his or her mind.
Most states allow an advance directive to be revoked orally, under certain safeguards.
Because this can lead to uncertainty and dispute, it is far better to change your advance directive in writing. You may also change your health care proxy in the same way. Advance directives can be whatever you want. Format is a matter of state law and should be followed precisely. Every hospital has advance directive forms suitable to its state's laws.