I have some ?? re: the original problem. [if you think I'm getting into that er vs icu thing, you're mistaken]
Do you have a medical director for your unit? Is s/he aware of this situation? Can they support you and your staff?
Do you have any kind of acuity classification system that you are using? If you did, the numbers would support your staffing.
Have there been any errors? Meds, treatments missed, orders not done, labs not phoned back or reported to the MDs? Have there been any "near misses"? If so, be sure that an Incident report [or whatever it is in your hospital] is used to document the problem. In our hospital, they are called "quality variance reports" and whenever something happens or doesn't happen that causes the care the patient and family receives to be less than what the "core values" of the institution state, we fill them out. That makes someone accountable--even if that "someone" is staffing--or lack thereof! We fill them out all the time--if pharmacy doesn't bring a med on time, if equipment doesn't work, if the lab screws up, if a patient's d/c is delayed. One of our managers then has to follow/up, and decide what needs to be done, sends it to the other department for eval, and eventually risk management gets it.
Sooo, this manager that is trying to limit staffing without taking acuity into account could wind up with a LOT of incidents to explain to someone else! Seems like it would be easier just to staff the unit correctly!!!