The latest update on John R.: while the buildup of fluid could still be connected to the difficulty of recalculating his dry weight for dialysis, another explanation that's been offered is one that unnerves me pretty badly, because my grandmother went through it. It could be congestive heart failure, as it's fluid in/around the lungs.
Aaaargh. :( THAT wasn't good news to wake up to.
Whatever it is, I hope they straighten out what his new dry weight is supposed to be, now that the bypass helps his heart to work better, so they can take the right amount of excess fluid out of his system during dialysis.