I have written a formal, witnessed statement of my wishes, in the event that I'm unable to utter them. My physician has a copy; there's a copy in my desk-drawer at home, with my will.
I understand that different health authorities here have different policies on the registration and application of such "living wills". I have no confidence that if I get sick in the wrong place, my statement will even be noticed, let alone respected. Also, there's no reason why a paramedic coming to my home would know to look in my desk-drawer (I live on my own), and so discover that I don't want any CPR, ever.
And ultimately, these living wills are advisory only; medics can't be sued for ignoring them.
It's a bloody mess. I really hope I don't ever get demented.
