What Is Active External Rewarming?

Another therapeutic measure that I've read about is so-called active external rewarming. And when might oxygen be necessary and what types of oxygen should we give? Yeah, so I think if a patient has a co-existent oxygen requirement, then oxygen should obviously be given, but we should aim to give it warmed and humidified. If a patient presents solely because of exposure and hypothermia and their oxygen levels are within normal range, then there wouldn't be any indication to administer any unless it was deemed an extra measure which could raise their body temperature. Thank you.