It sounds logical - or does it?

I'm an (inactive) RN, too.   I think that constipation is way under-"respected" as a problem.   I think you should probably talk with your doctor about it, but adding fiber to the full liquids shouldn't be a problem.   As soon after surgery as you are, you don't want to be involved in massive valsalva manoeuvers!    There are new kinds of laxatives that are non-dependency forming and more gentle than old ones.   Warm prune juice is fairly effective, also.

Even with full liquids, as you know, there are solids in the liquids.   Also the digestive bacteria "shells" make up a large portion of a BM.   So even with nothing but liquids, it's not normal not to have a BM.   Small, granted, but a BM nonetheless.

I took care of zillions of postop patients in ICU and a lot of the nurses thought constipation was kind of no big deal.   I think it's because they didn't really want to deal with it.   But I think it's better to deal with it when the problem is small (if you know what I mean) than deal with it when it becomes a big issue.

Good luck!

Dennie