From what I have found out, it is rare for O2 levels to drop below the high 90's, usually 97 to 98 %. But, a pulmonary event that causes O2 sat to be low would throw off a whole lot of blood chemistry. Getting that blood chemistry corrected would be important.

The toxic cascade of a concussion without an anoxic event would still have a negative impact on brain function. It's just like a CO or CO2 event. One can die from CO or CO2 poisoning with 20% oxygen available. The CO and CO2 block the absorption of oxygen just as toxins in the brain disrupt proper metabolism. That is the basis for the vitamin and supplements regimen, help the brain metabolise as it slowly detoxifies.

The injured brain is known to be more sensitive to O2 at altitude. This is a metabolic situation based on molecular pressure across cellular membranes. O2 sat is not the primary issue. It is molecular pressure. This is how HBOT works. It increase the molecular pressure. HBOT works with normal atmospheric O2 levels (20-22%). Pro's issue was his lungs were not absorbing the O2 so his O2 sat was low.