Worth noting that a decrease in end-tidal CO2 pressure (i.e., decreased amount of Co2 in an exhalation) is not in itself a statement about the amount of Co2 in tissues. A rudimentary analysis might even say that lower Co2 as measured in exhalation implies that more Co2 is retained in the tissues.

Bohr effect and others corroborate the idea that Co2 is not just a "waste gas" produced by respiration but has an important biological role in its own right.

Ingestion of baking soda, which supplies Co2 to tissues, is so effective at countering the effects of lactic acid from muscle overexertion that its administration is banned in horse racing.

It stands to reason that higher Co2 can protect against lactate throughout tissues, perhaps even including the brain, especially in a condition where the brain favors fermentation over respiration (as in cancer, per Warburg effect, and depending on who you ask, in mental illness/depression)