I'm not sure if Baku really did something like that. Out of the 4 used Bios, one of them was just before his suicide raise, and another one was right after when he was in "Think about every possibility" mode. Saving air for a single possibility of the endgame right from the start is pretty extreme. Assuming he really was doing it from the start though, he'd have at least 2 Bios with some air remaining, prepared for a situation in which the final Bios counts were relatively even. Hell, even having one of them with some air would freak Lalo out into breathing faster, so a 1-2 Bios advantage could be overcome.
Writing this up, it reminded me of Baku's little speech to Yakou after he chopped off his finger. The idea of paying a price, setting up a trick that may never truly be used, in order to fool people. Maybe Baku really was okay with dying on that raise without using up all the Bios, for the sake of tricking Lalo afterwards.