Good question. From the original Cell paper at https://www.cell.com/med/fulltext/S2666-6340(21)00153-7 https://www.cell.com/med/fulltext/S2666-6340(21)00153-7

Good question. From the original Cell paper at https://www.cell.com/med/fulltext/S2666-6340(21)00153-7 https://www.cell.com/med/fulltext/S2666-6340(21)00153-7 Interestingly, the arterial pressure of CO2 tended to be decreased in the l-EVA group, presumably due to the excellent O2 - and CO2-carrying capacity of perfluorochemicals (50 mL O2/dL and 160–210 mL CO2/dL, respectively), while the arterial pH did not change in our experiment. These results indicate that perfluorochemicals also act as an adsorbent for elevated CO2, indicating a need for future follow-up studies of gas exchange mechanisms. So, they speculate that some of it is absorbed by the perflourodecalin.