Thanks for getting back to me on this.
According to The Federated Ambulatory Surgery Association there are
more than 4,000 ambulatory (outpatient) surgery centers in the US:
Q. How long have outpatient surgery centers been in existence?
A. The first ASC opened in 1970. Today more than 8 million surgeries
are performed each year in the more than 4,000 surgery centers across
the United States.
The number appears to have trended upward in recent years, from the
An ambulatory surgery center or "ASC" is a health care facility that
specializes in providing surgery services in an outpatient setting.
...In the United States, over six million surgeries a year are
performed in approximately 3,300 ASC's across the United States.
...There are 3,644 Outpatient Surgical Centers in America today - a
50% increase since 1996. [thanks bobbie7-ga]
ASCs vs. Hospitals
...Today, there is a total of about 3,800 single-specialty and
multispecialty ASCs in the United States, Of these, about 700 to 800
are operated as ophthalmology-only centers.
It's difficult to always know exactly what dates are being referenced
by the above cites, but from the context of the pages, the data appear
to represent a recent increasing trend in the number of ASC's in the
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search strategy -- Google searches on:
outpatient surgical facilities
association ambulatory surgery
"2100..100000 asc" ambulatory