Acuity systems in hospitals

I work in a private hospital in Melbourne Australia and would like to ask if any private hospital out there has an acuity system in place.

I work on a 35 bed surgical ward as the Associate unit manager and feel the acuity system is justified however management do not seem to agree.

There are usually 6 staff members on the floor this means most nurses have a 1:6 ratio they are extremly busy especially on some nights when we can expect upto 16 or more returning post op some nurses are allocated four post op patients this i feel is to much.

I have spoken with management on an informal basis and as it is always suggested the girls have managed before why can't they manage now this i feel is because no one has spoken up.

To get management to even look at a proposal I need some strong evidence that this is a priority not only for the staff but for the best interests of our patients, the current public hospitals have a 1:4 ratio and they sometimes complain about that work load.

Any advice as to what i can do to get them to change there mind.