A Study in Quality: Ambulatory Surgery Centers vs. Hospital Outpatient Departments

There has been a recent trend for more and more surgeries to take place in ambulatory surgery centers (ASCs). In fact according to the Medicare Payment Advisory Commission, in 2004 up to 70% of surgeries took place in these ASCs. Do ASCs offer better quality surgical procedures than Hospital Outpatient Departments (HOPD)?

ASCs may be an improvement over HOPDs because these centers preform a high volume of a few specific procedures which may increase quality. Further, ASCs often have newer equipments than hospitals. On the other hand HOPDs generally have more resources than ASC to deal with complications and economies of scope may help hospitals to provide more effective care.

How do we find out which facility offers better quality? This question seems easy to answer: find a quality metric and measure whether ASCs or HOPDs score higher. The problem is that physicians may choose to conduct surgery on healthier patients at the ASC and perform the surgery on sicker patients in the HOPD. This way, if there are complications from surgery on a relatively sicker individual, the hospital will have more capabilities to deal with the situation. This selection problem, however, can bias studies which simply compare the quality levels of ASCs and HOPDs without taking into account difference in patient characteristics in each facility type.

A study by Chukmaitov et al. (HSR 2007) attempts to measure these quality differences using patient-level surgery data in Florida between 1997 and 2004. The authors attempt to eliminate the selection bias using physician diagnoses (i.e.: DRG/HCC methodology) to quantify the ex-ante and ex-post health status of the patient. The key to this methodology is that the authors also have information on any of the patients’ secondary diagnoses.

With this data, the author do in fact find that HOPDs do have a sicker patient base. Thus, it is important for researchers to correct for this selection problem. Secondly, Chukmaitov and co-authors found that “…neither organizational type (ASCs or HOPDs) performed better overall, there appear to be important differences in quality outcomes for certain procedures. These differences may be related to variations in organizational structures, processes, and strategies between ASCs and HOPDs.”

On problem with the study is that the authors use mortality as their quality metric. A more sensitive metric could better capture quality differences. Also, one may worry about the accuracy of the doctor diagnoses. HOPDs may be more sensitive to DRG creep than ASCs–or vice versa–and this may leaded to an incorrect selection correction methodology.

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