most people when they do a wean, with pmv or not have a trach mask with humidifier. ( the strait o2 is very drying). It all depends on the situation. I have seen o2 piped into the side port of a pmv. trach pts are neck breathers. so usually the situation is the above.
I am not an expert, but sometimes if a pt is not getting enough via the tm, then supplement o2 via nc is given.
Why dont you ask the person who this, the rationale behind. Just say " I was wondering the rationale behind that, not accusingly, just questioning"
Let us know. You have spiked my curiousity.