Why the desats my sweet baby girl?

Autumn woke me up just before 6am starting with her desats. She was running a low grade fever so I gave her Motrin along with her other 3 meds. Well, she was awake for about 30 mins then dozed back off. She's been desatting into the high 70's and 80's since then. Her lungs are clear...suctioned and was fine. Her breathrate is up and she's on a liter of oxygen. So, why the desats still? Sometimes when she get too many breaths or too much O2 she will desat so I tried that...nope, didn't work either. Gave a Xopenex treatment as well and still desatting. So I'm puzzled...her head is sunken in so I'm pretty sure her shunt is still working. I guess this mild broncitis is hitting her pretty hard. I hope once she wakes up her stats will go up. She's been on oxygen for over 24 hours straight. Praying she will feel better soon.