When I first became a firefighter over 30 years ago, we used “demand valve” masks delivering pure oxygen directly to patients who we were performing CPR on. We were able to pink up even people who had been down for quite a while, and with shocks and drugs we often got their hearts to start pumping again. We called this “a save”. This was very satisfying because we thought that we were helping them.
The problem which was noticed by medical providers who took care of the people we delivered to hospitals is that nearly all of the people who we used demand valves on were dead within a few days. People who received CPR using mouth to mouth and “bag valves” which deliver oxygen through a face mask by squeezing the bag had much better outcomes and survival.
Because people refused to believe that the demand valves were actually increasing mortality, despite ever-increasing evidence... we continued to use them for years. Who knows how many people whose lives our bull-headed attitudes killed. It is good to be skeptical, but some of the time our firmly held beliefs turn out to be wrong.
You can believe every word of it. We have know for quite a long time that oxygen contents higher than FiO2 of 60% free radical injury. We always strive whether intraoperatively or in ICU to limit oxygen inspiration to under these levels. The injury is time dependent as well. The longer the time the worse the injury in the organ systems.