Have been told the increase of carbon dioxide is the real danger of having low blood oxygen. Why doesn't some smart scientist invent a way to measure carbon dioxide other than a blood test? I had previously asked how much damage one could get from having blood ox in the 80s for a few hours and told the bigger concern would be high carbon dioxide.
High carbon dioxide doesn't always follow low blood O2 saturation, but it's definitely a factor and relatively common. If we're sick enough to be hospitalized, it's almost a sure thing that our CO2 is higher than normal and climbing. As for something other than a blood test, I know a bunch of people who've been trying to figure that out for a long time, but no luck so far.