You pee shortly before going to the OR so you're usually good for a few hours. There's a "first assist" which is usually a resident or PA scrubbed in helping. In long procedures there can be tedious dissecting so the attending can break scrub and go urinate or eat a quick snack while the resident keeps working. Only takes a minute or less to scrub in these days (Avagard replaced the old 4 minute scrubbing, and the scrub tech will have your gown and gloves ready for you) so that's not a barrier at all.