title: Opening ambulatory surgery centers and stone surgery rates in health care markets.
abstract: OBJECTIVE
  Ambulatory surgery centers deliver surgical care more efficiently than hospitals but may increase overall procedure use and adversely affect competing hospitals. Motivated by these concerns we evaluated how opening of an ambulatory surgery center impacts stone surgery use in a health care market and assessed the effect of its opening on the patient mix at nearby hospitals.
  
  
  METHODS
  In a 100% sample of outpatient surgery from Florida we measured annual stone surgery use between 1998 and 2006. We used multiple regression to determine if the rate of change in use differed between markets, defined by the hospital service area, without and with a recently opened ambulatory surgery center.
  
  
  RESULTS
  Stone surgery use increased an average of 11 procedures per 100,000 individuals per year (95% CI 1-20, p <0.001) after an ambulatory surgery center opened in a hospital service area. Four years after opening the relative increase in the stone surgery rate was approximately 64% higher (95% CI 27 to 102) in hospital service areas where a center opened vs hospital service areas without a center. These market level increases in surgery were not associated with decreased surgical volume at competing hospitals and the absolute change in patient disease severity treated at nearby hospitals was small.
  
  
  CONCLUSIONS
  While opening of an ambulatory surgery center did not appear to have an overly detrimental effect on competing hospitals, it led to a significant increase in the population based rate of stone surgery in the hospital service area. Possible explanations are the role of physician financial incentives and unmet surgical demand.
authors.affiliation: Robert Wood Johnson Foundation Clinical Scholars Program, University of Michigan, Ann Arbor, Michigan, USA.
authors.forename: John M
authors.initials: JM
authors.lastname: Hollingsworth
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Krein
authors.forename: John D
authors.initials: JD
authors.lastname: Birkmeyer
authors.forename: Zaojun
authors.initials: Z
authors.lastname: Ye
authors.forename: Hyungjin Myra
authors.initials: HM
authors.lastname: Kim
authors.forename: Yun
authors.initials: Y
authors.lastname: Zhang
authors.forename: Brent K
authors.initials: BK
authors.lastname: Hollenbeck
mesh_terms: D000554:Ambulatory Care Facilities / Q000706:statistics & numerical data*; D000556:Ambulatory Surgical Procedures / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010044:Outpatient Clinics, Hospital / Q000706:statistics & numerical data*; D013503:Surgery Department, Hospital / Q000706:statistics & numerical data*; D014545:Urinary Calculi / Q000601:surgery*