My plan or Dietician never once mentioned sodium and I had high BP pre-surgery. But, you eat SO minimal and it's basically all protein especially this early post-op that your sodium intake is going to be super low regardless if you watch it or not. When you get further out, you could over due it especially with eating out. (If you do)
With that being said, NOW i have LOW blood pressure, to the point it drops so low and quick that I have passed out a few times. I have learned to notice the signs and can usually rebound it before it gets that bad. But, now I have to watch and try to increase my sodium levels to help keep my BP stable. To the point I have licked salt off of my hand because there is nothing salty around. It is not as bad as I may have just made it sound, once we figured it out it balanced out and rarely happens. Also, there are meds to raise my BP if needed but since we got it stable I don't need meds.
Sorry for my rant: My point is don't stress it, you aren't going to have a high enough sodium intake to retain water like that.