has he been diagnosed with renal failure or are you just going by some of the symptoms?
what are you feeding, have you tried a variety of different foods...especially wet/canned food that has a good source of protien and no grains?
he really needs to see a Vet to get some blood work done if he hasn't already, there could be other reasons for his symptoms. the Vet can give some medication to help with the nausea and acid...that could also help his appetite..