The American Bar Association explained living wills in the article, "Living Wills, Health Care Proxies, & Advance Health Care Directives," available at americanbar.org, accessed on Mar. 27, 2018:

“A living will is your written expression of how you want to be treated in certain medical conditions. Depending on state law, this document may permit you to express whether or not you wish to be given life-sustaining treatments in the event you are terminally ill or injured, to decide in advance whether you wish to be provided food and water via intravenous devices (‘tube feeding’), and to give other medical directions that impact the end of life. ‘Life-sustaining treatment’ means the use of available medical machinery and techniques, such as heart-lung machines, ventilators, and other medical equipment and techniques that will sustain and possibly extend your life, but which will not by themselves cure your condition. In addition to terminal illness or injury situations, most states permit you to express your preferences as to treatment using life-sustaining equipment and/or tube feeding for medical conditions that leave you permanently unconscious and without detectable brain activity.

A living will applies in situations where the decision to use such treatments may prolong your life for a limited period of time and not obtaining such treatment would result in your death. It does not mean that medical professionals would deny you pain medications and other treatments that would relieve pain or otherwise make you more comfortable. Living wills do not determine your medical treatment in situations that do not affect your continued life, such as routine medical treatment and non life-threatening medical conditions. In all states the determination as to whether or not you are in such a medical condition is determined by medical professionals, usually your attending physician and at least one other medical doctor who has examined you and/or reviewed your medical situation. Most states permit you to include other medical directions that you wish your physicians to be aware of regarding the types of treatment you do or do not wish to receive.”

Mar. 27, 2018