Oxygen Levels Can Go Way Lower Than We Once Thought

During COVID, we had patients walk into the ER on their own two feet. And they talked to us. And when we asked, "Are you feeling short of breath?" You would get the answer, "No. My breathing is fine." 

And we knew this not to be true. We saw that their saturation was in the 70s. And yet you saw a patient sitting on the edge of their bed talking away. And this sort of changed our perception of a low oxygen saturation. 

In the past, we saw sats in the mid 80s as horribly bad. When COVID hit, we decided that it was okay to maintain sats in the mid to low 80s, so long as the patient was doing okay. If they showed signs of failing, only then did we think of using BiPAP and intubation. And this was how we learned to manage hypoxia due to COVID. 

We learned to be patient. We learned not to panic about sats in the 70s. 

Now, does that mean we did not treat the hypoxia? No! If I had a patient with sats that low, I'd be setting up a high flow nasal cannula. I'd set the flow as high as I could (like 60 or 70 if needed). And I'd set the FiO2 at 100%, or as close to it as I could get given the device I was using. 

And if this maintained a sat in the mid 80s, and the patient was seemingly fine otherwise, I'd be patient. If the sats dropped, I'd have the patient try proning. And in many instances this worked just fine. 

There were times I had a patient do just fine (well, given the situation) on 100% FiO2 high flow nasal cannula, mixing in proning, for weeks. And they would get better at times and we'd reduce the flow and FiO2, and they would get worse again. This cycle would continue until they either eventually got better or required more invasive treatment. 

What we learned is that humans can tolerate low oxygen levels way better than we once thought. We had one patient on 100% Fio2 for an entire week with sats in the 70s. This was during the heartof the first surge when we didn't know much about COVID. 

And eventually this patient started to fail. His respiratory rate increased to 40 or higher. His body was starting to shut down. And he eventually decided to let us intubate him. And even just before he was being intubated, he was mentally fine. I had a discussion with hem. 

And, I think, in retrospect, we should have intubated this man much earlier. And if he didn't make himself a DNR we may have. Still, experiences such as this has us rethinking low oxygen levels. It has us rethinking hypoxia and its effects on the human body. 

Personally, I do not think our current definitions of hypoxia should be changed. I think 88-90% is a good bottom line to maintain. With COPD, we have learned to tolerate sats in the 88-92% range. And for COVID we have learned to tolerate sats in the mid 80s. We certainly do not want it to stay that low too long.

But, given that intubated COVID patients have a 50% chance of dying. I think that being patient bodes well for them. 

How long can a human being tolerate a sat in the 70s? We do not know for certain. Eventually their body will shut down. But, we do know that the body has fighting power to maintain oxygenation to vital organs way longer than we once thought. And a person has the ability to maintain normal functions for way longer than we thought. They can talk. They can think.