The University of Chicago Medical Center is changing the way it admits emergency room patients as part of its effort to deal with the worsening economy, a move underscored by its announcement of 450 layoffs, or 5% of its workforce. The decision to introduce what amounts to a new version of patient triage represents an aggressive and unusual move by one of the city's premier hospitals to cope with spiraling costs and the long waits for emergency treatment. Some don't like the plan, but the U. of C. says it has no choice: The academic medical center said 40% of the 80,000 patients who go to its emergency room each year do not need to be there. These visits cost the hospital tens of millions of dollars a year.