How does a living will support a person who may be unable to communicate his or her wishes in the event of permanent incapacitation?

Answers will vary. A living will is a legal document that people usually draft before their terminal illness that directs health-care workers not to use aggressive medical procedures or life-support equipment to prolong vegetative functioning in the event they became permanently incapacitated and unable to communicate their wishes. Terminally ill patients can insist, for example, that "Do not resuscitate" orders be included in their charts, directing doctors not to use CPR in the event they suffer cardiac arrest.
Living wills must be drafted in accordance with state laws. The living will only takes effect if people are unable to speak for themselves. For this reason, living wills usually identify a proxy such as the next of kin to make decisions in the event that the signer cannot communicate.