Im really sorry. I have dealt with the same thing. I had a kid post cleft pallet repair. She was unusually dry. This surgeon usually has larger than average blood loss. An hour and a half after I transfered her she coughed and started aspirating a large volume of blood and coded. Ended up trached. I have gone over everything many many times. The floor nurse said that she was fine till she coughed.

It is just the process. If you aren't blowing things off as "not my problem" you are doing the right thing. It's how we learn and get better. Shit happens. Just keep doing the best you can and make sure to keep learning. No matter what, stuff like this will happen. It is just how it goes.