Has anyone had to get a blood vessel cauterized in the nose of their (possibly autistic) 2 year old?

My son just turned 2 on September 15th. He's had suddenly started having frequent nosebleeds since the 14th. He went to his pediatrician on Monday, who said that normally nosebleeds are nothing to worry about but since his are sudden and frequent, he's referring him to an ENT.

Now, I talked to the ENT this morning. The earliest opening they had is October 8th. And she said what normally happens is that they have to cauterize a blood vessel in their nose with silver nitrate. Of course, she said she's not certain what will have to be done yet as they won't know what is causing the nosebleeds until he is seen.

Now my son is very averse to anyone touching his face. He is very likely on the autism spectrum and his speech therapist agrees, but they don't want to evaluate him for autism until he is 3. And my son is very delayed communication-wise (hence the speech therapist). Not only is he nonverbal, but he doesn't understand much of anything I say to him. So explaining to him that he needs to be calm and the doctor is going to put something in his nose to help him isn't going to do much.

She said if he just absolutely freaks out and moves enough that they can't do it without hurting him, they will have to do it in the operating room where they can put him under to do it.

Of course, I don't want it to come to that. I'm worried about traumatizing him. But he had four nosebleeds in one day one time, so I don't think it's something I can wait to fix itself.

So to anyone who has had to have this procedure done on a child so young (especially one who is or may be on the spectrum), how did you keep your child calm during/before/after the procedure?