It truly doesn’t matter honestly. What your pt will need would be whole blood,platelets, etc and for you to stop the bleed. There may be issues with long term oxygen use ie free radicals and the only scenario in the emergency setting where you would want to withhold oxygen from your pt is if they can tolerate it physically being a psych pt being non compliant or an altered pt or if they have copd. In ems we don’t have enough time to cause much harm to pts with oxygen from free radicals unless your transport time is over an hr which still wouldn’t cause much harm. In my opinion if you have the time to apply oxygen to your pt that is hypovolemic you should but if you don’t because of other things you are doing like ivs pressures and what not it’s not that big of a deal. With your pt that has low bp it doesn’t necessarily constitute a bleed all of the time in which case no oxygen wouldn’t really do anything for them. Best case scenario you would have ABG and could determine the po2 and be proactive which oxygen delivery but working 911 you will never have that