They start my daughter on o2 whenever she dips down into the low 90's, anything much under 95. But she is very young, and her sats are usually at about 95 , so anything under that and they begin to worry. They always make her stay on it untill she can maintain at or close to 95 on room air, which can sometimes take days depending on what we are dealing with. I don't know if they base it on age or what your normal sats are, but that is just her, and like I said she is very young.
