“I shot an intruder in self defense.”
That is NOT what to say. DO NOT admit you shot anyone except on the advice of your lawyer.
You have to say something to the 911 operator so the cops know you are the homeowner and not an armed criminal. The word intruder is important. It’s not a bad idea to give the operator a description of yourself as well, just to be sure they don’t shoot you, especially if you are holding a suspect at gunpoint. I don’t think there’s anything in that one line that can harm you in court. Beyond that, shut up.
Tell the cops that you’re having chest pains and find it hard to breath.