My 83-year old father-in-law already has moderately bad dementia, but is about to get a cancerous kidney removed. The local anesthesiologist raised the same concern about __possibly__ making the dementia worse and wanted no part of it. But he's got cardiac clearance (another issue) and anesthesia clearance at a more specialized university hospital and a date already set for his surgery.

So, I guess it's a legitimate concern, but worth taking somewhere else for a specialist's second opinion.

I hope you'll post back here if you learn anything more. Best of luck!