We Almost Lost Her...Twice

I am going to start at the beginning where all this craziness started. On Thursday night they had removed her breathing tube to replace it with a bigger one. The size she had in has been the same size since birth and obviously she has grown but the tube has not. So because the tube was small, air was leaking around the tube and she wasn't getting it all in her lungs.
So to replace the tube they paralyzed her for a few minutes during the change. Afterwards she slightly recovered from it and then went down hill. She needed 100% oxygen setting on the ventilator (lately she had been needing 21-35%) and her oxygen saturation in her body was only in the 70s (she is normally in the mid 80s-high 90s).
When we got to the hospital yesterday morning the nurse told us how touchy she was. Every time she had care done her oxygen would drop and they would have to take her off of the vent and bag her until it came back up, which didn't always work. They were giving her medicine to help her relax and for pain just in case that was the issue although that seemed unlikely.
Then around 11:30 am her oxygen dropped again and this time her heart rate went with it. They had to do chest compressions because her heart rate dropped into the low 60s (her normal is 120-150). They were able to quickly correct the problem but she still was rocky.
Around 4pm it happened again but was worse than the 1st time. Her heart rate dropped into the 40s as did her oxygen level. They had to give her medicine to try to speed up her heart because the compressions weren't doing it. It seemed like forever until they stabilized her enough that they could even walk away from the bed. I was seriously waiting for them to turn to us and say that there was nothing more that they could do, but they didn't!
After this second "episode" they gave her medication to paralyze to which allows the ventilator to do all the work for her. Mike and I slept here at the hospital in a parent's room in the NICU. I checked on her every couple of hours and each time I went in the oxygen setting on the ventilator was lower. This last time it was at 21%, the lowest it can go!
She is definitely not out of the woods yet and they have no clue why this happened. First they thought maybe her heart defect was over flooding the lungs with blood so they did an ultrasound of her heart, which came back good (well good for her anyway). Then they thought maybe an infection but all of the blood work for that is normal. Her chest x rays look good too. So whatever it is is unknown, which means they don't know the solution until they find the problem!
Please say some prayers for our girl in hopes that she won't go through anymore of this!