You did the right thing. I a pt will no tolerate a mask some O2 is better then none. I don't understand your bosses reasoning for wanting to get a spO2 reading first because as you said the pt was in obvious distress it should not have mattered what his spO2 was. That should be used as a guide only anyway just to make sure that your treatment is actually working. As an ems first responder you do not have to worry about knocking out a pt breathing because you give him "too" much O2 it takes hours to actually do that. And regardless if he stops breathing because you gave him O2 you just breath for him anyway.
Also asthma is a COPD.
