On Friday, March 20, 2020 at 4:35:27 PM UTC-6, son_of_flubber wrote:
A pulse-oximeter quantifies pulmonary function.

What is the O2 saturation that should trigger a trip to the E-room?

It depends. For normal healthy people anything in the low 90s is abnormal and needs to be evaluated. However, for someone with COPD, who normally lives in the upper 80s to low 90s, it could be normal to have an O2sat of 89%.

If you are feeling bad and your O2 sat is in the low 90s (90-93%), then get checked. If you aren't sure, get checked. It's better to be safe than sorry.