We know that while performing Tiruvaradhanam or tharppanam or sandhyavandanam, one must not have the urge to urinate. All of these should have been taken care of before starting. Very elderly people, will not be able to contain the urge due to their advanced age. If they happen to go for urination during these, they will have no choice other than to bathe again. If that is not possible, at least they must perform mantra snanam and start right from the beginning instead of continuing from where they left off.
Usually, people will be very careful during Tiruvaradhanam. If one happens to go for urination in the middle of a Tiruvaradhanam, one bath again and commence the Tiruvaradhanam right from the beginning. Else, one can get one’s son to perform the Tiruvaradhanam. When it is not possible to a complete bath, one can perform mantra snanam.
All these considerations apply only to very elderly people and not those who are of robust health. One must complete all the ablutions before Tiruvaradhanam, sandhyavandanam, etc. There must be no compromise in this.