Ambulatory surgical centers, free-standing facilities where patients can go for minor procedures, continue to proliferate in Pennsylvania, making big profits for theirs owners, a new report shows.

As of May, there were 261 ambulatory surgical centers across the state after a net gain of 14 new centers between June 2008 and May, according to the Pennsylvania Health Care Cost Containment Council. Their number has more than quadrupled the past 10 years, said PHC4 Executive Director Joe Martin.

More notably, the average total profit margin of the centers -- the ratio of total income to total revenue, a strong indicator of overall financial status -- has increased to 26.06 percent, with an average 2 percent gain each year since 2001. That's because they now account for more than 60 percent of the increasing number of outpatient diagnostic and surgical procedures, the report says.

But the ambulatory centers' gain has meant a financial loss for the state's 179 acute care hospitals, says the Hospital and Healthsystem Association of Pennsylvania.

Because the ambulatory centers draw patients who are healthier, and often fully-insured, "the financial strain and clinical demands on acute care hospitals, which serve as the safety net for all Pennsylvanians, are growing," said association President and CEO Carolyn Scanlan in a statement.

Total margins for acute care hospitals averaged 0.38 percent statewide in fiscal year 2009, according to the association.

The PHC4 report analyzed financial data for centers providing ambulatory surgical care, rehabilitation services, psychiatric care, long-term acute care and specialty care.

Total margin for the state's 21 rehabilitation hospitals improved slightly to 11.49 percent, while the 17 free-standing psychiatric hospitals -- which does not include Western Psychiatric Institute and Clinic -- averaged a 5.96 percent total margin, up from 5.69 percent the year before.

Total margin for the 26 long-term-care facilities dropped slightly to 2.07 percent.

PHC4 reports are available online at www.phc4.org.

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