A Power of Attorney (POA) can be, with the correct wording, unrestricted in both the duration of time and scope of task. Thus people will insist their appointment by an enduring unrestricted POA is enough for them to make health decisions for the donor, and arguably they could be correct.
Historically the POA was designed to deal with business and other financial needs. It is important to remember the objective is to have a document that makes the health crisis less stressful, and it is important to remember that every bureaucracy likes its own forms. So rather than argue with the hospital staff in the middle of the health crisis, it is better to just ask your local health authority now in advance if the POA is acceptable to your local hospital.
For example, in BC there is a BC Health Ministry with different health districts - and most things are online so it is easy to just email to ask eg https://www2.gov.bc.ca/gov/content/health
Your lawyer can help you make an Advance Directive in addition to a Representation Agreement which can state your current wishes about health decisions in certain circumstances as well as appoint your "representative" to make health and financial decisions. See all the free information about BC options on this website www.nidus.ca
Remember that information and forms are no more than that - and beware your wishes can change over time. If you need advice then you need a lawyer.