Mild osa symptoms have been improving in 4 year old after encouraging daytime nose breathing v. mouth. is it possible mouth breathing is causing osa?

Apnea: More likely enlarged tonsils and adnoids are the problem. Have him evaluated by an ent.

No: Unfortunately not. Mouth breathing can be a sign of osa. It is also possible that your child has nasal obstruction from allergies. You also want to have the tonsils and adenoids evaluated for removal.

R/O OSA: UNLIKELY it is an anatomical problem due to large Tonsils/Large uvula. OSA can be suggested with underling obesity/small oral airway.The definitive test is a PSG with split night/CPAP titration. I would request copy of sleep study and get a second opinion if you are not satisfied with the options. CPAP can be difficult to tolerate. ENT FOR UPP EVAL.