Interesting question. At the inpatient psych hospital I work at, we work 8 hour shifts and have 2 units: An adult-dual diagnosis unit with 25 beds and a geri-psych unit with 14 beds. All things being equal, we try to have at least 3 RN's staffed between the 2 units during 1st and 2nd shifts, and one RN on each unit for 3rd shift. The A/D unit generally gets the 2nd nurse, until census and/or acuity reaches the point on the geri unit where we need a 2nd RN (usually around 10 or so patients or less if there is cathing to be done, tube feedings, trach care or the like). A/D unit generally needs 2 RN's on their unit unless really low-census since they tend to get more admits/discharges (typical stay on our A/D unit is about 3 days versus about 14 days on the geri-ward).
Now, to muddle the issue, my hospital doesn't currently use an acuity rating system to determine staffing needs. We did use a paper & pencil system once upon a time, but now-a-days we have a census grid which determines staffing levels for RN's and techs based only on patient numbers, not acuity. So, whichever nurse is currently playing charge subjectively determines the needs of each unit and staffs accordingly. Most times this works, sometimes it doesn't. Some nurses want a second nurse to work with, some would rather have a second tech.
This all leads me to a closely related question, how are other inpatient psych hospitals determining their staffing needs? Just by the numbers? Or is someone out there using an objective, acuity based system? And is your staffing system working? This has been a burning question for myself and the nurses I work with as we strive to maintain a safe, healing environment for our patients.
Thanks, and good wishes to you...