Ah fuck I got goosebumps. So many years reading this manga, wasn’t expecting that at all though. The old Ijuuin would’ve said “but I’m just an intern” and needed to be convinced that he has what it takes, but no.
And I don’t even think it’s a matter of self-confidence or anything of the like. I think he trusts Asada and (to a lesser extent) Katou, and in the deepest sense truly has faith in their prowess as doctors as well as leaders. They told him to perform the surgery, hence he must be capable of performing the surgery. It’s as simple as that.