Growth of ambulatory surgical centers, surgery volume, and savings to medicare.

We studied the impact of the growth of ambulatory surgical centers (ASCs) on total Medicare procedure volume and ASC market share from 2000 to 2009 for four common outpatient procedures: cataract surgery, upper gastrointestinal procedures, colonoscopy, and arthroscopy. ASC growth was not significantly associated with Medicare volume, except for colonoscopy. An additional ASC operating room per 100,000 population results in a 1.8% increase in colonoscopies performed in all outpatient settings. Increases in the number of ASCs were associated with greater ASC market share with effects ranging from 4- to 6-percentage-point gains for each additional ASC operating room per 100,000. The study demonstrates that continued growth of ASCs could reduce Medicare spending, because ASCs are paid a fraction of the amount paid to hospital outpatient departments for the same services.