A very important point to note is that your attorneys under a Health and Welfare LPA may not make decisions regarding life-sustaining treatment unless you specifically authorise them to do so.
An Advance Decision allows you to refuse specified medical treatment at a time in the future when you can no longer make that decision for yourself. A Health and Welfare LPA allows you to give general authority to your attorneys to consent to or refuse life-sustaining treatment; it is not necessary to specify a particular treatment.
If you have made an Advance Decision, and then make a Health and Welfare LPA and give your attorneys this general authority, the Advance Decision is revoked. However, it will continue if you do not give your attorneys this general authority under a Health and Welfare LPA.