I would ask the vet to walk you through the procedure--will they be pushing IV fluids (good for older dogs), what anesthetics will they be using, will their be pain relief during treatment, what exactly will be done during treatment, how does wakeup work, what drugs if any will be used post-procedure. What will be the costs, with a breakdown for the different parts. A good vet, imo, should be willing to explain all this to you, and you'll probably feel better understanding all of it.
I wait through Patrick's procedure (not necessary, but I worry), it usually takes maybe an hour total between pre-op stuff to him coming out, then I leave while they monitor him for several more hours, and come back and pick him up later in the day.