I think you mean Acepromazine (ACE). It's not technically an anasthetic, but a pre-anasthetic sedative. It shouldn't be used on boxers because it is known to dramatically lower their blood pressure, sometimes leading to heart failure. If your vet is intent of using a sedative ahead of anasthetic, then valium will do the job just as well, without the same risk of death.
A search here on the terms Ace* or Acepromazine should bring up all the information you need.