Mortimer Schnerd, RN wrote:

We will routinely put anybody with an SaO2 of less than 90% on oxygen in the
hospital where I work. I generally run around 95% myself on room air.

What you do in the hospital is one thing, what you need to be able to
safely fly is an entirely different thing. In our glider club, we have
equipped all gliders with an EDS pulse demand oxygen system. We think we
have been flying noticeably better since we've routinely used it as low
as 7000ft and certainily are less tired in the evening.

Stefan