Durable power-of-attorney remains effective after the principal's incapacity. The principal can give several agents different types of powers to manage his/her (1) financial matters or (2) healthcare matters, i.e. to take decisions on medical treatment.
In Germany, notaries public recommend that spouses give each other such powers, because a 85-year old mentally incapable cancer patient in the last phase of life may not be given strong pain-killers, if he/she has no proxy for medical decisions and cannot himself/herself make any will. The doctors fear that the patient "may become drug addictive".


--------------------------------------------------
Note added at 21 час (2007-01-03 08:57:00 GMT)
--------------------------------------------------

On checking the legal meaning of "durable" I suggest a new wording:
"доверенность на принятие медицинских решений, действующая в случае недееспособности доверителя ".

My answer is based on the following documents:
1. http://courts.co.calhoun.mi.us/book023.htm#2.
What is a Durable Power of Attorney?
A Durable Power of Attorney is a written power of attorney which contains the words "This power of attorney shall not be affected by my disability," or "This power of attorney shall become effective upon my disability," or similar words. In order to be valid it must be signed by you before you become disabled.

2. http://www.caringinfo.org/i4a/pages/index.cfm?pageid=3444
Medical power of attorney - A document that allows an individual to appoint someone else to make decisions about his or her medical care if he or she is unable to communicate. This type of advance directive may also be called a health care proxy, durable power of attorney for health care or appointment of a health care agent. The person appointed may be called a health care agent, surrogate, attorney-in-fact or proxy.