The living will and medical power of attorney have similarities, but are not the same. Both legal documents are part of an estate plan. Most people find it comforting to have both the living will and medical power of attorney in place.
Part of estate planning is planning for a time when you cannot make decisions for yourself; this includes health care decisions. The living will documents you making a specific health care decision ahead of time. The medical power of attorney documents your selection of an agent to make health care decisions on your behalf.
The Living Will
A living will is a legal document that authorizes medical measures that may hasten your death but keep you comfortable. It also authorizes the withholding of medical measures that would serve to artificially extend your life. It may be helpful to think of a living will as preventing heroic measures such as being hooked up to machines, while brain dead, for 17 years (i.e. Terry Schiavo.)
A living will is only effective if you are at the very end of life. It is not effective if you are in good health and have a health issue or suffer injury. Most living wills dictate that heroics may not be used if you are in an irreversible coma, vegetative state, or otherwise terminal and at the very end of life.
A living will represents your medical decision made, during a time when you were competent to make the decision, which is only effective at a later time. Your agent under a medical power of attorney cannot override your living will.
The Medical Power of Attorney
The medical power of attorney is similar to a financial durable power of attorney (sometimes called a general durable power of attorney), except is effective for health care decisions only, not financial decisions other than that the authorization of medical care that costs money.
In a medical power of attorney, you name an agent to make health care decisions when you can no longer make those decisions. While it is common to name your spouse or children, it is wise to select an agent who is comfortable with medical terminology and dealing with doctors.
If you have questions regarding why you need a living will and medical power of attorney, consult with a qualified estate planning attorney.