I think that your are very appropriate to feel uncomfortable abou being
ordered to take care of a vent dependant patient.
Always think of your level of traning and experience. If you don't have the trainng then your supervisors have no right to ask to do something out of your scope of practice.
I hae worked in aspect of critical care for 20 years. That would be like asking me to work a shift in the newborn nursery. I don't have the proper experience or training to do that.
Keep sticking to your guns and refuse the assignment until you are offered the proper educational experiences and the clinical orientation to do the job.
PRF