Since this is a ‘how does the law work’ question based off of a situation in a television show, I don’t think it counts as asking for actual legal advice so I’m starting it in GQ.
How does privilege work if someone else is empowered to make medical decision for you. If Abe is temporarily given medical power of attorney over Bob, and later they have legal conflict and Abe wants to talk about what he did in a legal proceeding Bob brings against him, what information can he reveal without if Bob doesn’t waive doctor-patient privilege? I presume the existence of the power of attorney is public record, and if there was an order involuntarily giving someone that power, but I think details of any medical records would be protected. I’ll outline the situation from the show in case it helps:
In the show Better Call Saul (set in NM), Chuck got a head injury and was taken to the hospital where they believed he needed an MRI. He also has a mental condition where he believes electromagnetic radiation hurts him, so he was refusing treatment. His brother Jimmy got a temporary medical power of attorney because the Doctor supported a claim that Chuck wasn’t competent, and Jimmy used it to consent to having Chuck sedated and given an MRI, which determined he was OK. After that, Jimmy gave up the power of attorney.
Later on in the show, Jimmy and Chuck are at odds with each other. Chuck is going to claim at a bar hearing (though I’m also interested in court) that Jimmy confessed to illegally modifying documents to make it look like Chuck was incompetent. He has a tape of Jimmy confessing to modifying the documents. Jimmy is (probably) going to argue that his brother is mentally unstable to the point of being a danger to himself, and that Jimmy never modified the documents, he just made the statement to Chuck because he thought Chuck might hurt himself otherwise. As part of the evidence, I’m sure Jimmy would like to include the statement from the doctor that Chuck wasn’t competent, the fact that he had to get a medical power of attorney, and the fact that he voluntarily relinquished it once the situation was over (in the show it was apparently possible for Jimmy to have Chuck committed). So what of that could Jimmy use against Chuck’s will and what would be protected?