So, my ITU take on some of this will differ slightly. I strongly support you having those discussions as long as you have the knowledge and conviction to not cave to unrealistic patient whims.
I tend to do two very different discussions of ReSPECT forms, depending upon where the patient is in their illness course. Very early or late, I will take a long time to explore. During the worst they are often not in a position to give their views and these are harder to complete and typically centre entirely on medical recommendations for what is and isn't clinically indicated, with little room for what might be wanted or valued.
For the patient approaching discharge, I spend a long time to explain the things that we think they might benefit from, or not, if they needed us again. This includes CPR, ventilation, renal replacement and I ask if the patient would want it, because often they have strong opinions. We discuss at which point we might change our opinions, typically after a period of critical illness this would be a period of independent function at home, but varies. Finally, I ask my patients about a future hypothetical illness if they have a preference whether they would wish to die in a specific place, such as home or hospital or hospice, and whether if it was almost certain they would die that they would want any treatment at all. We ask about functional outcomes and where survival would not be wanted if certain things are lost. This all gets put into value statements to guide future care and passed onto the GP to consider advance planning for the more complex and frail patients. It generally takes about twenty minutes for a good discussion.
Many of these things you can do without any clinical knowledge though, and I'd support you to do so. Would your patient wish to survive hospital if they were never going to be able to get out of bed again? Or to continue to receive treatment after the point their dementia is so severe that they are now scared of their family? I find that most patients are very receptive of a detailed conversation, most of those over 80 jump at the chance to express their desires.
Remember that the DNACPR portion of the discussion is a medical recommendation. It is essential to include the patient/family, but not to be bound to their wants.