Many US hospital-affiliated freestanding ambulatory surgery centers are located on hospital campuses, relevant to interpretation of studies involving ambulatory surgery

Abstract

Study objective: The US Agency for Healthcare Research and Quality's State Ambulatory Surgery Database includes procedures performed at hospital outpatient surgery departments. We hypothesized that, among US hospitals with an anesthesia department and freestanding outpatient surgical center, the prevalence on hospital campuses (i.e., within 250 yards of the main hospital building) would be sufficiently large (e.g., >10%) to influence interpretation of observational studies performed with US national ambulatory surgery datasets.

Design: Randomly selected Medicare certified hospitals in the USA surveyed during a two-week period in February 2017.

Setting: Observational cohort study of 500 unique hospitals.

Measurements: Freestanding surgery centers were obtained from a review of the websites of the hospitals. Google map street view was used to measure linear distances of the closest hospital-affiliated ambulatory surgery center with anesthesia provider(s) to each hospital's main building.

Main results: There were 124 hospitals with the website listing an affiliated ambulatory surgery center within 10 miles of the main campus. Of the 124 facilities, 53 were freestanding. Of the 53, there were 22 (42%) located within 250 yards, 95% confidence interval 29.1% to 55.9%, P < 0.0001 versus 10%.

Conclusions: The percentage of freestanding surgery centers located within 250 yards of main hospital buildings is sufficiently large to influence analyses. When using US national data, ambulatory surgery reported as performed at a hospital should not be considered as having been performed within the hospital. Similarly, hospital affiliated freestanding surgery centers should not be assumed to be more than a 5 min walk for anesthesia and operating room personnel from the hospital.