A Medical Power of Attorney (MPOA) allows you to appoint an agent to make medical decisions for you when you are unable to make those decisions yourself. Those decisions may cover the giving or withholding of Band-Aids clear up to life support. The MPOA does not say what your wishes are; just who you want to act on your behalf.
A Physicians Directive, also known as a Living Will, is a document that says specifically if you do or do not want life support in the event that you are terminally ill or have an irreversible condition. The specific instruction of a Physicians Directive will control over the general appointment of an Agent under a MPOA. You do not have to have an Agent present to make the decision for you with the Physicians Directive.
We recommend that everyone prepare a MPOA, and your personal situation and preferences will determine if a Physicians Directive will be beneficial for you.