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To the Editor: Fueled by the high prevalence of morbid obesity, bariatric surgery centers are proliferating rapidly across the United States.¹ Reports of serious complications and deaths have raised concerns that many hospitals perform too few bariatric procedures and lack the necessary staffing and facilities to perform these complex procedures safely.¹ Some private insurers are selectively contracting with hospitals meeting "centers of excellence" criteria, which include minimum procedure volumes and specific requirements for staffing, services, and facilities. The American College of Surgeons² and the American Society for Bariatric Surgery³ have initiated credentialing processes for hospitals offering bariatric surgery based on similar criteria.

Because of this, we examined trends in the numbers of patients undergoing bariatric surgery in high-volume and low-volume hospitals, as well as the size, staffing patterns, availability of specific services, and other characteristics of hospitals offering bariatric surgery relative to other US hospitals.

Methods
We analyzed data for 1997-2003 from the Agency for Healthcare Research and Quality's Nationwide Inpatient Sample. These data include 5 million to 8 million inpatient stays from 750 to 1000 hospitals each year from the states participating in the Healthcare Cost and Utilization Project.⁴ In the Nationwide Inpatient Sample, hospitals are stratified by ownership and control, bed size, teaching status, urban or rural location, and US region. Probabilities proportional to the number of hospitals in each stratum are used to approximate a 20% representative sample of acute care, nonfederal US hospitals.⁴ We identified patients undergoing bariatric surgery in the Nationwide Inpatient Sample database using appropriate International Classification of Diseases, Ninth Revision (ICD-9) procedure and diagnosis codes.⁵ For each year, hospitals performing bariatric surgery were categorized according to annual procedure volumes (low, <50; medium, 50-100; or high, >100).^{1, 6} Sampling weights for patients and for hospitals were used to calculate national estimates of numbers of bariatric procedures and hospitals.⁴ We used data from the American Hospital Association's 2003 annual survey to examine the characteristics of hospitals performing bariatric surgery and to compare them with all US hospitals offering inpatient surgery. Characteristics between hospital groups were compared using ² tests for proportions and Wilcoxon rank-sum tests for medians. P values <.05 were considered statistically significant. All analyses were performed using SAS software version 9.1.2 (SAS Institute Inc, Cary, NC).

Results
Between 1997 and 2003, the number of US hospitals offering bariatric surgery nearly tripled, from 413 (8.5% of all hospitals) to 1111 (23%). Among hospitals performing bariatric surgery, median annual procedure volumes increased from 7 procedures (interquartile range, 2-58) in 1997 to 46 procedures (interquartile range, 13-124) in 2003. In 1997, 5% of hospitals performing bariatric surgery did more than 100 procedures per year, compared with more than 30% by 2003.

A declining proportion of procedures was performed in low-volume hospitals. The proportion of patients undergoing bariatric surgery in a high-volume center increased from 39% to 77% (Figure), while the proportion performed in a low-volume hospital decreased from 32% to 9%. In 1997, the 10% of hospitals with the highest bariatric surgery volumes performed approximately 57% of all procedures. In 2003, the top 10% were responsible for 42% of all procedures.

View larger version (30K): [in this window] [in a new window] Figure. Estimated Number of US Patients Undergoing Bariatric Surgery by Hospital Procedure Volume and Year

Relative to all US hospitals performing inpatient surgery, hospitals offering bariatric surgery tended to be larger, as measured by bed size, utilization, staffing, and availability of specific services (Table).

View this table: [in this window] [in a new window] Table. Comparison of the Characteristics of Nationwide Inpatient Sample Hospitals in the 2003 American Hospital Association Survey*

Comment
Although our study is limited by lack of data about individual surgeon volume (a component of standards established by the American College of Surgeons and the American Society for Bariatric Surgery), our findings suggest that most of the growth in bariatric surgery rates has occurred in relatively large, high-volume hospitals. These trends were attributable more to overall increases in procedure utilization than to increased market concentration. Nevertheless, by 2003 the large majority of bariatric surgery patients were treated by hospitals with sufficient experience performing these procedures. Restricting bariatric surgery to facilities performing more than 100 procedures per year, as some guidelines suggest,^1-2 would eliminate almost 70% of currently performing hospitals but would affect only the 23% of patients having procedures performed in the low-volume centers.

Focusing on the setting in which surgery is performed may be a necessary but insufficient step toward ensuring the safety and effectiveness of bariatric surgery. Future efforts should focus on creating the clinical data infrastructure needed to assess and improve quality at all centers, not just those with low volume.

Access to Data: Dr N. Birkmeyer had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Financial Disclosures: None reported.

Funding/Support: None.

Nancy J. O. Birkmeyer, PhD
nbirkmey{at}umich.edu

Yongliang Wei, MS; Aaron Goldfaden, MD; John D. Birkmeyer, MD
Michigan Surgical Collaborative for Outcomes Research and Evaluation (M-SCORE)
Department of Surgery
University of Michigan Health System
Ann Arbor

1. Kelly J, Tarnoff M, Shikora S, et al. Best practice recommendations for surgical care in weight loss surgery. Obes Res. 2005;13:227-233. WEB OF SCIENCE | PUBMED 2. Bariatric Surgery Center Network (BSCN) Accreditation Program. American College of Surgeons (ACS) Web site. Available at: http://www.facs.org/cqi/bscn/index.html. Accessed November 24, 2005.3. ASBS Bariatric Surgery Centers of Excellence. American Society for Bariatric Surgery, Surgical Review Corporation Web site. Available at: http://www.asbs.org/html/about/coe.html. Accessed November 24, 2005.4. Design of the HCUP Nationwide Inpatient Sample. Rockville, Md: Agency for Healthcare Research and Quality; 2003.5. Flum D, Dellinger E. Impact of gastric bypass operation on survival: a population-based analysis. J Am Coll Surg. 2004;199:543-551. FULL TEXT | WEB OF SCIENCE | PUBMED 6. Nguyen N, Paya M, Stevens C, Mavandadi S, Zainabadi K, Wilson S. The relationship between hospital volume and outcome in bariatric surgery at academic medical centers. Ann Surg. 2004;240:586-594. WEB OF SCIENCE | PUBMED

Letters Section Editor: Robert M. Golub, MD, Senior Editor.

JAMA. 2006;295:282-284.

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