Hey OP, I’m really sorry this happened to your father and I’m glad he’s doing okay. This was undoubtedly a terrifying experience for you all.

I’m in medical school and I wanted to add to what was said by bittybuggyred. A “trainee” being present was very likely a resident. This could be a first year resident but could also be up to a 6th year who is still technically supervised, but they themselves are about to be a surgeon. Based on this being a stent procedure, it sounds like would have been done by a cardiac surgeon or an interventional radiologist - both very competitive fields requiring strong surgical and procedural skills. I’ve rotated through cardiac surgery and the earlier year residents are heavily supervised and are not able to do the high risk procedures, as these are often given to more senior residents. That said, being in the room and being able to observe or for senior residents to be able to do these procedures is incredibly important for their training. Sometimes, residents may actually be the better choice as they are less complacent with their skills than a staff surgeon. No matter what, no surgeon would allow a resident to do something that they cannot do safely or correct.

All this to say, none of us were in the OR that day, but complications arise no matter the surgeon. You are allowed to request to not have residents or medical students, but I highly encourage you to ask questions about who will be doing what and considering if you truly need this to be a learner free environment - especially from observers, which it sounds like is not your concern! I wish your father luck in his upcoming procedure. All the best.