Geographic and Institutional Trends in Ambulatory Surgery in the State of California, 2012-2014.

Although geographic variation in health care services is well established, relatively less is known about ambulatory surgical procedures in California. Thus, we sought to describe statewide trends according to geographic and institutional factors. Using the California Office of State Health Planning and Development Ambulatory Surgery and Hospital Utilization datasets, overall and per-capita procedure rates by county and institution were calculated and compared across 2012 to 2014. There was substantial variation in services provided at the county level (Range: 49-382,142 cases/county). Among the 10 largest counties, there was a more than 2-fold difference in case volume per capita; across all counties, a 50-fold variation was observed. Changes in county population size and surgical case volume were correlated only if Los Angeles, the most populous and highest-volume county in the state, was excluded as an outlier. In the first year of California's full Medicaid expansion, Medicaid ambulatory surgery cases increased 29 per cent and self-pay cases decreased 16 per cent. The top 10 facilities by volume experienced substantial volatility in case volume over two years, ranging from -19.6 to +11.5 per cent. Geographic differences in rates of ambulatory surgery may be related to population shifts, but this was not uniformly true. The factors driving this variation and its impact on patient care warrant further investigation.