I was going to recommend Dr. Bredesen’s work, so I was glad to see you had already found it! I think it’s solid.
However, I worry that because your relative’s dementia seems to have been brought on by anesthesia, the mechanisms may not be the same. I’m sorry I don’t know what to recommend in that case.
There is a paper (sorry but don’t have the reference here) that describes how 2 groups of elderly patients had surgery. One group (control) inhaled air each day for a period of time before the operation. The other group inhaled hydrogen.
The hydrogen-inhalation group had significantly less post-op delerium.
So it appears that hydrogen may prevent some delerium. Not sure if it can help after the event. BUT I did read a case study of a woman with Alzheimers who was incontinent. She breathed hydrogen for 2 hours per day for a couple of years (!) and improved enough such that she was no longer incontinent. So it could help, but it’s not a quick fix.