What would cause a 13-month-old baby with CLD and mild PLA stenosis to experience a fluctuation in saturation levels?

Hi doctor,

I am writing regarding my daughter, who is 13 months. She has failed to thrive and has a few other issues, including CLD (no oxygen requirement), and mild LPA stenosis. We still have a monitor at home that we want to keep until she turns one year. Recently I noticed that her saturation is not as good when she’s deeply sleeping. It used to be between 96 % and 98 % when she was asleep, and now it has between 94 % and 96 %. Sometimes it goes down to 87 % but only for a second and then goes straight back up to 94 %, 95 % and remains stable. Why does she have very short drops for not even a second that goes as low as 87 %? She never turns blue, she seems to be sleeping deeply, and she’s fine during the day. She eats a lot and is happy, but only when she’s sleeping deeply.

I noticed that her saturation is better when we give her time to digest after her last meal. I have the feeling that when she falls asleep right after eating, then it takes 3 or 4 hours when she’s sleeping for her saturation to be around 96 to 97 %. When she falls asleep right after her last meal, it seems her saturation is lower (it is always above 92 %), but sometimes it goes down to 87 % for not even a second and then goes straight back up. Could it be that she has gas in her stomach, pushing her lungs?

We give her some caloric formula because otherwise, she is not gaining weight, so maybe she’s struggling to consume it at night. I hope she does not have any other heart issues, and I hope it is not related to her heart. Her last echocardiogram was done two months ago, and the doctor said it was fine except for the mild LPA stenosis, but she said it is very mild, and she does not need any surgery and will probably never need one as long as it remains mild. Could something else have come up in the last two months?

Please give your suggestions.