In the US, a "vent" comes with a complex list of other skills and responsibility. The RTs are responsible for the alarm systems and doing their own cleaning and decontamination as well as set up for the next use. This can get time consuming and it is rare an RN will have an extra 30 minutes or more to get a machine back in service especially if the pre-use test is not going well.
Some hospitals also have a little policy about tubes. Don't mess with what you can not put back in or don't have the time to bag until someone comes to put it back in. If an RT loses a tube while retaping, they can either re-intubate or they will bag until someone who can arrives which could be several minutes or many, many minutes if the patient is stable with the BVM.
There is also the setup of, monitoring and changing of the other gases such as Nitric Oxide, Heliox, Nitrogen and Carbon Dioxide. Few RNs can take the time to go to the loading dock for more tanks and do all the change outs with the pipe wrench especially on night shift. Even switching out all the machines on one patient can be time consuming if first BiPAP was trialed, then intubation and a regular ventilator and then HFOV. Add another gas or two or setting up a continuous medication drip like flolan as well as cleaning all the equipment can be a pain. In some places it is nice if the RT also has the responsibility of the IABP and the A-lines. They will usually have their protocols so you don't have to wait for a physician to come in the next day and make time to insert an arterial line.
RTs in the US have a minimum of an Associates degree with many having a Bachelors degree and some have a Masters if they are involved in education, research or management. Much of the advancement in ventilation/oxygenation science have come about and changed by the research done by this group.
Canadian Respiratory Journal, Home
A hospital can run a lot of different ventilators and in a variety of modes. Most RTs work off protocols as long as they get the desired results. The RN may also have protocols just for keeping the patient stable for the various modes. If a patient is not tolerating a ventilator well or deteriorating fast and needs to be stabilized, it is really easier to work with someone else on the other side of the bed as a team instead of thinking you can fly back and forth across the best trying to titrate 5 drips and make several ventilator changes all the while making sure your alarms are also in compliance. It just takes one mistake on either team member to have a disaster on top of what might already be a train wreck.
But, with all that being said, many hospitals and LTC facilities are cutting back on RTs. If you want the total responsibility of "managing" a ventilator, you can go to one of the many subacutes. Or, you can allow the RTs to train you on everything about ventilators and join a flight team. If you want to do all of you own treatments, just work med surg or the ER in some hospitals. But few RNs want or can spend 30 - 60 minutes with one patient just doing a treatment protocol like for a spinal/neuro or CF patient.
Hospitals also do not get reimbursed for "therapy" if done by a nurse and it is not cost effective to add more RNs who make at least 2x what an RT makes. The choice was made to give up a lot of floor treatments but in the long run we are now seeing a problem with that decision.
At your hospital in Australia, did you make all the ventilator decisions for choosing the machine and mode changes as well as gas/drug titration on your own?