Ok. The whole sentence is:
Person A bandages Person B's arm.
Person B says: ありがとう。ずいぶん慣れた処置ね？看護婦でもやってたの？
I get what the sentences are saying.
But! For the life of me I can't parse ずいぶん慣れた処置ね？ into that makes any sense to me. All I can come up with is: "You do very accustomed treatments." Which I know barely makes any sense (grammatical or otherwise).
Can someone please break this down for me?