Hmmm, that's a tough one. Maya had a GA when she was 2 1/2 and she was fine, the anaesthatist explained everything on her level and she wasn't scared or anything but she was a lot younger than Quinn, I imagine he will be a lot more aware of what's going on. When we were kids we used to have a book about a kid that went to hospital to have an operation (my brother was in and out of hospital a lot) which explained everything at an age appropriate level, maybe your local library would have something similar?
Best of luck, let me know if you need anything, I am the hospital queen after all!