Welcome! Also, odd place to post this question
1) Airlock bubbles are not a sign of fermentation. The only sure fire way of knowing if fermentation has started to ceased is to take a gravity reading. How long has it been in primary? Have you taken a gravity reading?
2) There is not going to be any oxygen in your headspace since the CO2 created during fermentation pushed it out and created a blanket of gas (CO2 is heavy.)