WASHINGTON – The annual number of outpatient surgery visits in the United States increased 67 percent between 1996 and 2006 to 34.7 million, according to a report from the federal Centers for Disease Control and Prevention. The CDC says that reimbursement changes helped lead to the rise.

The CDC report, "Ambulatory Surgery in the United States, 2006," notes that the number of visits to freestanding surgery centers tripled during the 10-year period to 14.9 million per year, while the number of visits to hospital-based surgery centers remained relatively unchanged at 19.9 million per year.

The most common outpatient surgery procedures in 2006 included endoscopies of the large or small intestine and extractions of the eye lens.

The report attributes the growth in outpatient surgery visits to advances in medical technology and changes in payment arrangements.

For instance, in the early 1980s, the Medicare program was expanded to cover care in ambulatory surgery centers, and a prospective payment system based on diagnosis-related groups was adopted for hospital inpatient care that created strong financial incentives for hospitals to shift less complex surgery to outpatient settings.

Many state Medicaid plans and private insurers followed the lead of the Medicare program and adopted similar policies.

The growth of managed care along with consolidation of hospitals, has also furthered the growth of ambulatory surgery, the report notes.

The number of freestanding ambulatory surgery centers grew from 239 in 1983 to over 3,300 nearly two decades later. The number of procedures being performed in ASCs also increased dramatically-from 380,000 procedures in 1983 to 31.5 million in 1996.

The CDC's findings are based on 2006 data from the National Survey of Ambulatory Surgery, which was last conducted in 1996.