Ambulatory surgery centers and outpatient procedure use among Medicare beneficiaries.

BACKGROUND: There has been a strong push to move outpatient surgery from hospital settings to ambulatory surgery centers (ASCs). Despite the efficiency advantages of ASCs, many are concerned that these facilities could increase overall utilization.
OBJECTIVE: To assess the impact of ASC opening on rates of outpatient surgery.
DESIGN: This was a retrospective cohort study of Medicare beneficiaries undergoing outpatient surgery between 2001 and 2010. We compared population-based rates of outpatient surgery in Hospital Service Areas (HSAs) with freestanding ASCs to those without. After adjusting for differences using multiple propensity score methods, we assessed the impact of ASC opening in an HSA previously without one on rates of outpatient surgery.
SUBJECTS: Patients included were Medicare beneficiaries with Part B eligibility. MAIN OUTCOME MEASURE: Adjusted HSA-level rates of outpatient surgery.
RESULTS: Adjusted outpatient surgery rates increased from 2806 to 3940 per 10,000 and the number of ASC operating rooms grew from 7036 to 11,223 (both P<0.001 for trend). By the fourth year after opening, rates of outpatient surgery increased by 10.9% (from 3338 to 3701 per 10,000) in HSAs adding an ASC for the first time. In contrast, outpatient surgery rates grew by only 2.4% and 0.6% in HSAs where an ASC was always or never present, respectively (P<0.001 for test between 3 slopes).
CONCLUSIONS: Rather than redistributing patients from one setting to another, the opening of ASCs increases outpatient surgery use. However, the 10.9% increase is more modest than previously suggested by state-level data.