A Living Will (otherwise known as an Advance Directive) can be used to record someone’s wishes concerning the medical procedures which are to be employed in the event of loss of mental capacity. A Living Will may also be used to record a person’s views on the medical care they receive should a difficult medical decision have to be made. This is sometimes called a Non-Directive Statement.
However, Living Wills are rarely used these days as a Lasting Power of Attorney is usually a far better way of dealing with these issues.