For years, estate lawyers have advised people to sign both a living will and a health-care proxy. The idea is that a living will gives you some say in your end-of-life medical decisions. You would prepare a health-care proxy (or a health-care power of attorney) in case you are temporarily incapacitated or develop a debilitating condition, and you want a specific person to make medical decisions for you.

This is fine in theory, but problems arise when the two sets of medical directives meet in real-life situations. Based on our talks with lawyers, ethicists and members of families involved, we think it's time for most of us to shred our living wills and instead talk seriously to the person we've named as our agent.

A living will states your wishes for medical care at the end of your life. It is generally used only when you are terminally ill or unconscious and cannot be revived. Your living will expresses your wishes for treatment under these conditions or even your desire to withhold treatment. This usually includes whether you want cardiac resuscitation if your heart fails or if you want to be placed on a mechanical respirator.

A health-care proxy designates another person to make medical decisions on your behalf when you are incapacitated. You do not have to be terminally ill or unconscious, but your agent may also act in such situations.

You can change or revoke a living will and a health-care proxy at any time, as long as you are mentally competent.

A health-care proxy is broader and more encompassing than a living will, which is why having both documents in force can tie the hands of the person you most trust to make difficult ethical and emotional decisions concerning your care. That can happen if there appears to be a conflict between what the living will says and what your agent believes you would have wanted.

When a conflict arises, hospital officials and their lawyers must try to decipher whether your particular situation activates the terms of the living will. The simple yes-or-no decisions you outlined on paper now invoke a series of value judgments and decisions involving your doctor and your family, as well as the hospital.