No new innovation or power shift away from insurers

Austin Frakt over at incidental economist has a nice graph showing the shift from 1990 to 2000 of the proportion of surgeries that were performed in inpatient v. outpatient surgery centers. In 1990, nearly 6 in 10 surgeries were inpatient; a decade later, it was the opposite. Now in 2010, the proportion has been the same since 2000. Why the change from 1990 to 2000? And why no more change in the past 10 years?

My thoughts on the most likely reasons why these trends are observed.

• There was a 'play out' in innovation related to either anesthesia care or post-op care that meant that the trend toward outpatient surgeries 'stalled out.'
• There was a shift in the relative power in the health care marketplace. In 1990, the health insurers held relatively more power, whereas by 2000 the power had shifted to providers (defined as hospital and most notably health systems.). This is similar to Austin's 'demise of managed care' explanation.
  

One thing I would be interested in seeing/knowing: are there differences in the inpatient v. outpatient surgery proportions by the type/size of hospital? Put another way, if you remove large health systems, would the proportion of surgeries inpatient v. outpatient look the same? I honestly have no idea.