"We found that areas of the country that had higher numbers of vascular surgeons had more bypass surgery performed and lower amputation rates," said principal investigator Vivian Ho, a health economist at Rice's Baker Institute for Public Policy and an associate professor of medicine at Baylor.
PAD is a condition in which fatty deposits build up on the inner linings of arteries, restricting the flow of blood to muscles and organs, especially the kidneys, stomach, arms, legs and feet. About 8 million to 12 million people are affected by PAD. The disease accounts for about half of all amputations among diabetics and is the major cause of amputation for nondiabetic patients.
Treatment often entails lifestyle changes and medication. Sometimes amputations can be avoided through bypass surgery in the lower extremities that improves blood circulation in the legs and feet; this procedure must be performed by vascular surgeons.
Amputation rates can vary as much as tenfold in different areas of the U.S., so Ho wanted to analyze whether the availability of vascular surgeons in a region affects revascularization and amputation rates for patients with PAD. Collaborating with the University of Alabama in Birmingham and Intermountain Health Care in Salt Lake City, Utah, Ho identified all patients with PAD in the Medicare claims data in 1994 and tracked their claims through 1999. She separated data on more than 143,200 patients who survived through 1999 by hospital referral region and merged it with information on the supply of local physicians and vascular surgeons.
Ho's statistical analysis of the data revealed that a .30 increase in the number of vascular surgeons per 10,000 Medicare beneficiaries resulted in almost a 1 percent increase in bypass surgery rates and a 1.6 percent reduction in amputation rates.
The study suggests that the likelihood a patient with PAD undergoes revascularization might depend on access to vascular specialists. But Ho found a "substantial disparity" in the supply of vascular surgeons across the country. Although this disparity might be expected, due to differences in the incidence of PAD in various regions of the nation, Ho found that even after allowing for the varying rates of the disease by location, the supply of vascular surgeons was strongly related to the attractiveness of an area. The nation's 1,500 vascular surgeons treating Medicare patients are more likely to live in locations with high rankings in "Places Rated Almanac," which compares cities in terms of recreation, education, transportation, arts, cost of living, climate, crime rate, health care, jobs and other marketing criteria. "Regional variability in specialists who treat PAD is influenced by factors other than regional medical needs," said Ho, who is also an associate professor of economics at Rice.
She noted, for example, that Houston ranks No. 8 in the "Places Rated Almanac" and has 50 percent more vascular surgeons per capita than Corpus Christi, Texas, which ranks No. 179. In turn, the amputation rate among Medicare beneficiaries in Houston is only half that found in Corpus Christi (2 versus 4.35 per 10,000 Medicare beneficiaries).
Ho also studied the availability of interventional radiologists, who can perform angioplasty in the lower extremities of patients with PAD to improve circulation. "We found weaker evidence that greater availability of interventional radiologists increases angioplasty rates and reduces amputation rates," Ho said.
"What surprised me most about the study is the disparity in the supply of specialists and the fact that so much of the variation in the supply is determined by where the specialists want to live rather than where they are needed most," she said.