I've been meaning to bring this one back for a while, but everything I've found has been either too easy or too clearly just some closeup of some part of the anesthesia machine. See some past "name that medical equipment" editions here, here, here, here, here, and here.
(The comments section on the three oldest posts do not show any comments because I was using a different and now defunct comment hosting system back then. If you are DYING to know if you were right in your guess, I will post the answers to these old entries tomorrow.)
OK, I'm on call tonight. See you on the other side.