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Obstetrics & Gynecology:
doi: 10.1097/AOG.0b013e31821647a0
Original Research

Effect of Surgical Volume on Morbidity and Mortality of Abdominal Hysterectomy for Endometrial Cancer

Wright, Jason D. MD; Lewin, Sharyn N. MD; Deutsch, Israel MD; Burke, William M. MD; Sun, Xuming MS; Herzog, Thomas J. MD

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Author Information

From the Division of Gynecologic Oncology, Department of Obstetrics and Gynecology, and the Department of Radiation Oncology, Columbia University College of Physicians and Surgeons, and the Herbert Irving Comprehensive Cancer Center, New York, New York.

Supported by the Milstein family fund.

Corresponding author: Jason D. Wright, MD, Division of Gynecologic Oncology, Department of Obstetrics and Gynecology, Columbia University College of Physicians and Surgeons, 161 Fort Washington Avenue, 8th Floor, New York, NY 10032; e-mail: jw2459@columbia.edu.

Financial Disclosure The authors did not report any potential conflicts of interest.

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Abstract

OBJECTIVE: To estimate the effects of surgeon and hospital volume on perioperative morbidity and mortality in women who underwent hysterectomy for endometrial cancer.

METHODS: Patients who underwent abdominal hysterectomy for endometrial cancer between 2003 and 2007 and who recorded in an inpatient, acute-care database were examined. Procedure-associated intraoperative, perioperative, and postoperative medical complications, as well as hospital readmission, length of stay, intensive care unit (ICU) use, and mortality were examined. Surgeons and hospitals were stratified into volume-based tertiles and outcomes analyzed using multivariable, generalized estimating equations.

RESULTS: A total of 6,015 women were identified. After adjustment for case-mix variables and hospital volume, perioperative surgical complications (15.2% compared with 11.7%) (odds ratio [OR] 0.57; 95 confidence interval [CI] 0.38–0.85), medical complications (31.4% compared with 22.0%) (OR 0.57; 95% CI 0.37–0.88), and ICU utilization (8.9% compared with 3.5%) (OR 0.47; 95% CI 0.28–0.80) were lower in patients treated by high-volume surgeons. Surgeon volume had no independent effect on the rates of operative injury (OR 0.82; 95% CI 0.32–2.08), transfusion (OR 2.33; 95% CI 0.93–5.36), length of stay (OR 0.60; 95% CI 0.25–1.41), or readmission (OR 1.05; 95% CI 0.51–2.14). Whereas patients treated at high-volume hospitals were less likely to require ICU care (9.3% compared with 4.3%) (OR 0.44; 95% CI 025–0.77), hospital volume had no independent effect on any of the other primary outcomes of interest (P>.05 for all).

CONCLUSION: Perioperative surgical complications, medical complications, and ICU requirements are lower in patients treated by high-volume surgeons. Hospital volume had little independent effect on outcomes.

LEVEL OF EVIDENCE: III

Endometrial cancer is the most common gynecologic malignancy in the United States, with more than 40,000 new cases diagnosed annually.1 Despite the frequency of the disease, considerable controversy exists regarding its management. The route of primary surgery and the necessity and extent of lymphadenectomy are actively debated.2 Even more controversy exists surrounding adjuvant therapy, and to date, standard protocols for the postoperative treatment of women with endometrial cancer are largely lacking.3 Despite these uncertainties, the management of most women with newly diagnosed endometrial cancer begins with hysterectomy.

In general, hysterectomy is safe and associated with reasonable morbidity.4 Although a number of studies have explored the disparities in treatment and survival for women with endometrial cancer, relatively few data have examined the quality and outcomes of hysterectomy for endometrial cancer.5 Whereas patient-related factors are known to influence perioperative morbidity, there is growing recognition that physician and hospital characteristics also affect outcomes for a number of procedures.6–12 Of the physician and hospital characteristics, one of the most important determinants of outcome is volume, those patients treated by high-volume surgeons and at high-volume hospitals have improved outcomes.6–9 The volume outcome paradigm has been reported for a number of high-risk cardiovascular and oncologic procedures.6–9

Despite the growing recognition of the importance of physician and hospital characteristics on outcome, data describing how these factors affect the outcomes of women with endometrial are largely lacking. The goal of our analysis was to estimate the effect of physician and hospital volume on outcomes for women who underwent hysterectomy for endometrial cancer. We performed a population-based analysis of women with endometrial cancer who underwent abdominal hysterectomy to determine the association between surgeon and hospital volume and perioperative morbidity and mortality.

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MATERIALS AND METHODS

An analysis of data from the Perspective (Premier) database was performed. Perspective is a voluntary, fee-supported database that collects inpatient data from more than 500 acute-care hospitals from across the United States. The Perspective database was developed to measure quality and resource utilization. Data submitted to Perspective are updated quarterly and audited regularly to ensure the quality and integrity of the data. Perspective comprehensively records data on patient demographics, clinical characteristics, procedures, outcomes, and all billed services. The Perspective database has been validated and utilized in a number of outcomes studies.13–15 Our study was approved by the Columbia University Institutional Review Board.

Patients who underwent abdominal hysterectomy (International Classification of Diseases, 9th Revision [ICD-9] codes 68.3, 68.39, 68.4, 68.49, and 68.9) for uterine cancer (ICD-9 182.0–182.8) between 2003 and 2007 were analyzed. Patients who underwent a minimally invasive hysterectomy, vaginal hysterectomy, or radical hysterectomy were excluded from analysis. Performance of lymphadenectomy was recorded for each patient. A unique physician identification number is provided for the surgeon who performs each procedure. We included only patients whose primary surgeon was a gynecologic oncologist.

Dependent variables in the analysis included age (younger than 50 years, 50–64 years, or 65 years of age and older), race (white, African American, other), marital status, date of diagnosis (2003–2005 or 2006–2007), insurance status (Medicare, Medicaid, commercial, uninsured), and region of residence (Midwest, Northeast, South, West). Comorbidity was estimated using the Charlson index.16 Hospital characteristics including location (urban or rural), type (teaching or nonteaching) and size (fewer than 400, 400–600, more than 600 beds) were recorded.

The major focus of the analysis was to estimate the association between volume and outcome. The volume of abdominal hysterectomies for endometrial cancer performed by each patient's surgeon and hospital was calculated. Annualized volume estimates were calculated as not all surgeons and hospitals contributed patients during each year of the study. Annualized volume was determined by dividing the total number of procedures performed by the number of years in which an individual surgeon or hospital performed at least abdominal hysterectomy for endometrial cancer. The annualized volume estimates were then inspected and surgeon and hospital cut-points selected to divide patients into three approximately equal volume-based tertiles: low, intermediate, and high.

Perioperative morbidity was assessed using ICD-9 coding for known hysterectomy-associated complications. For reporting, the following outcomes were assessed: 1) operative complications (bladder injury, ureteral injury, intestinal injury, vascular injury, other operative injury), 2) perioperative surgical complications (reoperation, postoperative hemorrhage, wound complication, venous thromboembolism), and 3) medical complications (cardiovascular, pulmonary, gastrointestinal, renal, infectious, neurologic). Length of hospital stay was defined as the number of days from the procedure until discharge. Rates of transfusion and intensive care unit (ICU) use were calculated. Readmissions within 60 days of the procedure for any of the complications defined above were recorded. Perioperative death was defined as death during the hospitalization during which the patient underwent the procedure.

Frequency distributions based on surgeon and hospital volume were compared using χ2 tests and one-way ANOVA. Individual complications were compared across surgeon and hospital volume strata and reported as unadjusted rates. Generalized estimating equations were used to analyze the outcomes of interest while controlling for other demographic and clinical variables. Models were constructed with adjustment for case mix as well as with adjustment for case mix and surgeon volume (when the primary variable of interest was hospital volume) and case mix and hospital volume (when the primary variable of interest was surgeon volume). To account for clustering, the generalized estimating equations were fitted to correct for within-surgeon correlation (when hospital volume was the primary predictor) and within-hospital correlation (when surgeon volume was the primary predictor).17,18 Odds ratios (ORs) for the primary outcomes of interest are reported comparing the low-volume and high-volume tertiles with 95% confidence intervals (CIs). All tests were two-sided. A P value less than .05 was considered statistically significant. All analyses were performed with SAS 9.2.

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RESULTS

A total of 6,015 patients who underwent hysterectomy for endometrial cancer were identified. The clinical and demographic characteristics of the cohort stratified by surgeon and hospital volume are shown in Table 1. Lymphadenectomy was performed in 4,288 (71.3%) patients. High-volume surgeons performed more than 30 procedures per year, intermediate-volume surgeons 14.6–30 operations, and low-volume surgeons had 14.5 or fewer procedures per year. High-volume hospitals performed more than 53 procedures per year, intermediate-volume 36.1–53, and low-volume hospitals performed 36 or fewer surgeries per year. Patients treated by high-volume surgeons were more often nonwhite, not commercially insured, unmarried, and living in the southern United States (P<.05 for all). High-volume surgeons were more likely to practice at large, urban, teaching hospitals (P<.05 for all). Patients treated at high-volume hospitals were more often African American, less likely to have commercial insurance, more commonly treated from 2003 to 2005, more often married, and more frequently lived in the southern United States, and had more medical comorbidities (P<.05 for all). High-volume hospitals were more often large, urban, and teaching facilities (P<.05 for all).

Table 1
Table 1
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Unadjusted rates of individual complications stratified by surgeon volume are shown in Table 2 and Figure 1. Ureteral injuries (P=.001) were more common in women treated by high-volume surgeons, and vascular injuries (P=.03) and other operative injuries (P=.03) were less frequent when compared with low-volume surgeons. Wound complications (P=.01) and cardiovascular (P=.01), pulmonary (P=.03), gastrointestinal (P<.001), renal (P<.001), and infectious (P<.001) complications all occurred less frequently in patients operated on by high-volume surgeons. In the unadjusted analysis of complications by hospital volume, ureteral injury (P<.001), wound complications (P=.02), venous thromboembolism (P<.001), and gastrointestinal complications (P<.001) were all more frequent at high-volume hospitals (Table 3 and Fig. 2).

Table 2
Table 2
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Fig. 1
Fig. 1
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Table 3
Table 3
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Fig. 2
Fig. 2
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After adjustment for case-mix variables and hospital volume, perioperative complications (15.2% compared with 11.7%) (OR 0.57; 95 CI 0.38–0.85) and medical complications (31.4% compared with 22.0%) (OR 0.57; 95% CI 0.37–0.88) were less common in patients treated by high-volume surgeons (Table 4). Likewise, ICU utilization (8.9% compared with 3.5%) (OR 0.47; 95% CI 0.28–0.80) was lower in patients treated by high-volume surgeons. Surgeon volume had no independent effect on the rates of operative injury (OR 0.82; 95% CI 0.32–2.08), transfusion (OR 2.33; 95% CI 0.93–5.36), length of stay (OR 0.60; 95% CI 0.25–1.41), or readmission (OR 1.05; 95% CI 0.51–2.14).

Table 4
Table 4
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After adjustment for case-mix variables and surgeon volume, hospital volume had no effect on operative injuries (OR 0.87; 95% CI 0.45–1.65), perioperative complications (OR 1.44; 95% CI 0.99–2.11), medical complications (OR 1.54; 95% CI 0.96–2.46), transfusion (OR 1.37; 95% CI 0.73–2.58), length of stay (OR 1.15; 95% CI 0.51–2.61), or readmission (OR 1.51; 95% CI 0.55–4.13). Patients treated at high-volume hospitals were less likely to require ICU care (9.3% compared with 4.3%) (OR 0.44; 95% CI 025–0.77). The unadjusted mortality was 1.1% in patients treated by low-volume surgeons compared with 0.4% for those operated on by high-volume providers. The odds ratio for death was 0.38 (95% CI 0.15–0.93) after adjusting for case-mix variables. The small number of deaths precluded adjustment for case-mix variables and hospital volume.

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DISCUSSION

Among women with endometrial cancer, we noted improved perioperative outcomes in those patients treated by high-volume surgeons. Perioperative surgical complications, medical complications, and ICU requirements were all lower in patients who were treated by high-volume surgeons. In contrast, hospital volume had little independent effect on outcomes.

The association between volume and outcome has been demonstrated for a number of cancer-directed surgeries; those patients operated on by high-volume surgeons and at high-volume hospitals have improved outcomes.6–9,17 The majority of these reports have focused on high-risk oncologic procedures that are associated with substantial morbidity.7,8 Volume appears to have less of an effect on outcomes for lower-risk procedures and on operations that are performed more commonly.19–21 Studies examining the effect of volume on morbidity in women undergoing hysterectomy have reported mixed results.17,21–25 An analysis of patients who underwent hysterectomy for benign disease in New York noted that morbidity and mortality were decreased when the procedure was performed by high-volume surgeons.22 In one of the only studies specifically examining the volume-outcome paradigm for uterine cancer, Díaz-Montes and colleagues noted a 48% reduction in in-hospital mortality in patients operated on by high-volume surgeons. There was no apparent effect of hospital volume on outcome.23 In our cohort, perioperative surgical complications as well as postoperative medical complications were reduced by 43% in patients treated by high-volume surgeons.

We noted that whereas surgeon volume influenced outcome, hospital volume had little independent effect on perioperative morbidity. In an analysis of Medicare patients, much of the variation in operative mortality was the result of surgeon and not hospital volume; survival was improved even in high-volume hospitals if the procedures were performed by high-volume surgeons.8 Although a number of factors undoubtedly underlie the effect of volume on outcome, for procedures like hysterectomy, surgeon characteristics appear to play a dominant role. Although surgeon characteristics may influence complication rates, previous work has shown that variations in hospital volume and quality are important factors predicting outcome in those patients who do experience a complication.12,26,27

In addition to volume, a number of physician characteristics including training and subspecialization likely influence outcomes.10,11,17,28 Previous studies of women with endometrial cancer have shown that patients treated by gynecologic oncologists are more likely to undergo comprehensive surgical staging and less likely to require adjuvant radiation.29,30 In a large sample of women with ovarian cancer, whereas neither surgeon nor hospital volume influenced mortality, those patients treated by gynecologic oncologists had improved outcomes.11 Given the lack of tumor characteristics in our data set, a priori we chose to include only patients treated by gynecologic oncologists to minimize case selection bias. Our results are notable in that even among subspecialists there appears to be a volume-outcome effect.

We recognize several important limitations. Given that the primary purpose of administrative data are for billing, we likely were unable to capture all perioperative complications. To minimize this bias we limited our analysis to major complications that have been examined in previous studies.31 The Perspective database lacks data on tumor characteristics. For women with endometrial cancer, tumor characteristics influence not only operative planning but also perioperative outcomes. Parameters such as stage and histology likely influenced our findings and would be important variables for risk adjustment if they were available. Whereas we were able to examine short-term morbidity and mortality, the Perspective database does not allow for longitudinal follow-up. Further work is ongoing to determine how surgeon and hospital volume influence the patterns of adjuvant care and long-term outcomes for women with endometrial cancer. Our study focused exclusively on women who underwent abdominal hysterectomy. As the use of minimally invasive surgery is rapidly increasing, further worked specifically evaluating the influence of volume on outcomes for minimally invasive hysterectomy is ongoing. Finally, whereas we noted significant volume-based differences in outcomes, our findings are clinically modest, especially when compared with other oncologic surgeries.

Our findings raise the question of how surgical volume should influence the care of women with endometrial cancer. Public reporting initiatives such as the Leapfrog group have recommended care by high-volume providers for a number of procedures and diseases. Emerging data suggest that for many high-risk surgeries there has been a gradual concentration of procedures to high-volume surgeons. In a study of patients treated across the United States, there was a 54% increase in the number of gastrectomies performed by high-volume surgeons from 1999 to 2005, a 31% increase in pancreatectomies, and a 23% increase in thyroidectomies performed by high-volume providers during the same timeframe.32 Although concentration of care to tertiary referral centers may be appealing, regionalization of care has proven difficult for patients and physicians alike, particularly for common procedures such as hysterectomy.33,34 Other strategies have focused on improving the care of low-volume providers with initiatives such as minimum volume requirements for credentialing, public reporting of quality metrics, and pay-for-performance programs.35–37

In conclusion, we noted that surgical volume is associated with outcomes for women with endometrial cancer who undergo abdominal hysterectomy. Perioperative morbidity and ICU usage are lower in women treated by high-volume surgeons. Hospital volume has little effect on outcome. Further work is needed to determine the long-term influence of surgical volume on outcome and to develop interventions to reduce volume-related disparities.

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© 2011 by The American College of Obstetricians and Gynecologists.

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