decannulation-sleep study questions

[tucker'smom]

Hi,
My son Tucker is almost three, he has a trach due to BPD, and he just got off night ventilation about a month ago.
For the test to get him off the vent, his CO2 levels stayed about 42-45 (need to be between 35-55). So he did great. They moved him from a 4.0 Bivona down to a 3.5, along with stopping the vent.

So last night we went in for the study, wearing a 3.0 Bivona, with a cap, to see if he can get decannulated. The tech hooked him up to the CO2 monitor, without the cap on his trach, and his CO2 level was in the 90s

He was not breathing hard, he was laughing, we thought it was wrong. She called the pulmonologist, he said that didn't make any sense b/c his blood gas was in the 40s a few weeks ago. She tried another machine, which still said his CO2 was in the 90s. It remained low to high 90s all night for the study, while his oxygen sat never went below 94%.

I am confused and disappointed. He seems to be doing so well, but maybe he is not?? I think the dr still does not quite believe the machines, but what else can he say?

Anyone had this experience?
Thanks