Report it to your superior. Let them handle it. If they suspect impairment, they have every right to draw a tox screen. By continuing to waste with this person, you are enabling them, if indeed he is using.
I sit usually when I am doing paperwork/computer. Sometimes, my scrub says " Gosh, You're sitting!" I try to stay in on the surgery. After being a scrub nurse for 6 of 13 years as an LPN/ORT, I know what a lazy circulator looks like!