Over the past two decades the association between procedural volume and surgical outcomes has been studied extensively.1,2 For many surgical interventions, outcomes are superior when the procedure is performed by high-volume surgeons and at high-volume centers.1,2 The improved outcomes achieved by high-volume health care providers are likely the result of a multitude of factors including greater technical skill, adherence to guideline-based treatment recommendations, and superior management of complications.3–5
The association between procedural volume and outcomes is most pronounced for high-risk oncologic and cardiovascular surgeries.1,2,5 For endometrial cancer, there appears to be an association between hysterectomy volume and outcomes, although the magnitude of this association may be lower than for other higher risk procedures.6,7 In one report, perioperative surgical and medical complications were approximately 40% lower among women with endometrial cancer who underwent abdominal hysterectomy when the procedure was performed by a high-volume surgeon.7 These findings have contributed, at least in part, to the increased referral of women with uterine cancer to gynecologic oncologists.8
Despite the association between surgical volume and outcomes for endometrial cancer, little is known about how these data have affected contemporary referral patterns and patient outcomes. We performed a population-based analysis to first examine changes over time in surgeon and hospital procedural volume for endometrial cancer and, second, to explore the association between these changes in volume and perioperative morbidity, mortality, and resource utilization.
MATERIALS AND METHODS
We used the Statewide Planning and Research Cooperative System for the analysis. The Statewide Planning and Research Cooperative System is an all-payer reporting system established by the New York State Department of Health.9–12 The database captures patient characteristics, diagnoses, services, and charges for hospital inpatient admissions and outpatient visits. Data quality is ensured by conducting periodic reviews and by comparing Statewide Planning and Research Cooperative System data with other Department of Health databases.
We identified women diagnosed with uterine cancer (International Classification of Diseases, 9th Revision ([ICD-9] codes 179, 182.x) who underwent hysterectomy from 2000 to 2014. The sample was limited to those women who underwent either minimally invasive (laparoscopic or robot-assisted, ICD-9 codes 68.31, 68.41, 68.51, 68.61, 68.71, 17.4x; Current Procedural Terminology codes 58541, 58542, 58543, 58544, 58548, 58550, 58552, 58553, 58554, 58570, 58571, 58572, 58573, S2900) or abdominal hysterectomy (ICD-9 codes 68.3, 68.39, 68.4, 68.49, 68.6, 68.69, 68.9; Current Procedural Terminology codes 58150, 58152, 58180, 58200, 58210, 58240, 58950, 58951, 58953, 58956, 58594). Women who had hysterectomy with coding before the hospital admission and those with missing or invalid surgeon identifiers were excluded (Fig. 1).
Demographic characteristics included year of admission, age (younger than 40, 40–49, 50–59, 60–69, 70 years or older), race–ethnicity (white, black, Hispanic, other), and insurance status (none, private, Medicare, Medicaid, other). Comorbidity was measured by calculating the Elixhauser comorbidity score and categorized as zero, two, or two or more conditions.13 For risk adjustment of operative morbidity, the performance of the following concomitant procedures was recorded: pelvic exenteration, omentectomy, debulking, lymphadenectomy, small bowel resection, colectomy, rectosigmoid resection, hepatectomy, bladder resection, diaphragm resection, splenectomy, anterior colporrhaphy, posterior colporrhaphy, incontinence repair, oophorectomy, and colpopexy.
We recorded the surgeon and hospital of record for each patient. For each hospital and surgeon, we calculated the mean annual volume as the total number of procedures the surgeon or hospital performed divided by the number of years in which the surgeon or hospital contributed at least one procedure.7,14 The association between volume and outcomes was explored using volume as a continuous variable as well as through classification of volume into quartiles.15 For surgeon and hospital volume, quartiles with approximately equal numbers of patients were defined by visually inspecting the data.
The outcomes of the analysis included perioperative morbidity, in-hospital mortality, and resource utilization. Morbidity was defined as the occurrence of an intraoperative, surgical site, or medical complication as previously described.16 A composite of all-cause morbidity as well as analyses of each individual group of complications was performed. As surrogates for resource utilization, we recorded transfusion, hospital length of stay, and hospital charges. Prolonged length of stay (LOS) was defined as a LOS above the 75th percentile for each type of hysterectomy.9 For each patient, total charges were recorded, adjusted for inflation, and reported in 2014 dollars. Excessive total charges were defined as having the inflation-adjusted total charge ranked above the 75th percentile for each procedure type.9
The number of patients, surgeons, and hospitals over time was reported and compared using Spearman rank correlation. The mean and SD of the surgeon and hospital volume were reported by year and the trend was tested using analysis of variance. Patient demographics, concomitant procedures, and outcomes were reported as frequencies and compared across the quartiles of surgeon volume and hospital volume using χ2 tests. The median, interquartile range, and range of the volume were also reported for each quartile and compared using Kruskal-Wallis tests.
A mixed-effects log-Poisson model was fit to determine predictors of treatment by the highest volume (by quartile) surgeons. The model included hospital volume as a linear term, age, year, race, insurance status, comorbidity, route of hysterectomy, concomitant lymphadenectomy and omentectomy. Hospital identifiers were included as a random intercept to account for clustering within hospitals. To examine the association between surgeon and hospital volume and each outcome, we fit similar models including surgeon and hospital volume as linear terms while adjusting for the other covariates described. As a result of the presence of clustering within surgeons and within hospitals, random-intercept terms in the regression models were included as nested random intercepts. All analyses were performed with SAS 9.4. All statistical tests were two-sided. A P value of <.05 was considered statistically significant.
We identified a total of 44,558 patients who underwent hysterectomy for endometrial cancer treated at 218 hospitals in New York. The number of surgeons performing cases each year decreased from 845 surgeons with 2,595 patients in 2000 to 317 surgeons who operated on 3,119 patients in 2014 (Fig. 2A) (P<.001). The mean surgeon case volume increased from 3 (SD=6) cases in 2000 to 10 (SD=16) cases by 2014 (P<.001). Similarly, the number of hospitals in which hysterectomies were performed decreased from 182 centers in 2000 to 98 hospitals in 2014 (Fig. 2B) (P<.001). Mean hospital volume rose from 14 to 32 cases over the same time period (P=.29).
The median procedural volume of physicians in the lowest volume quartile was two (interquartile range 1–2) per year and increased to 50 (interquartile range 46–57) per year in the highest quartile group (Table 1). Similarly, median procedural volume of the lowest volume hospitals was nine (interquartile range 5–18) and rose to 153 (interquartile range 127–242) at the highest volume centers (Table 2). Performance of minimally invasive hysterectomy was more common in women treated by high-volume surgeons (P<.001). High-volume surgeons were more likely to operate at high-volume hospitals. For example, 5.5% of the operations performed by low-volume surgeons were at high-volume hospitals, whereas 60.9% of the procedures performed by high-volume surgeons were undertaken at high-volume hospitals (P<.001). In a multivariate model, later year of surgery and the performance of concomitant procedures were associated with treatment by a high-volume surgeon (Table 3).
When stratified by surgeon volume quartiles, the morbidity rate was 14.6% among the lowest volume surgeons, 20.8% for medium–low, 15.7% for medium–high, and 14.1% for high-volume surgeons (P<.001) (Tables 4 and 5). Similar trends were noted for surgical site and medical complications in which the complication rates rose slightly for the medium–low and medium–high-volume surgeons and then decreased for the highest volume surgeons. The rates of prolonged LOS and excessive total charges were lowest for the high-volume surgeons (P<.001 for both). There was no statistically significant difference in the mortality rate across the quartiles.
When surgeon volume was analyzed as a continuous variable, there was no association between volume and overall morbidity, any of the specific morbidity subgroups, transfusion, or prolonged LOS (P>.05 for all) (Table 6). The rate of excessive charges decreased with increasing surgical volume, whereas the mortality rate increased.
When hospital volume quartiles were analyzed, morbidity increased at medium–low and medium–high-volume hospitals and then declined to the lowest rates in the highest volume hospitals (Table 4). Increased hospital volume was associated with lower rates of surgical site and medical complications, mortality, transfusion, and prolonged LOS (Table 4). The rate of excessive charges was 15.5% in low-volume hospitals, rose in the medium-volume quartiles, and then decreased to 23.9% in the high-volume quartile (P<.001). When hospital volume was analyzed as a continuous variable, increased volume was associated with a higher morbidity rate, increased transfusion, and excessive charges but lower mortality (Table 5).
These data suggest that practice patterns for endometrial cancer have gradually shifted over the past two decades with a concentration of patients to a smaller number of surgeons and hospitals. The association between surgeon and hospital volumes for endometrial cancer is complex with an increased risk of adverse outcomes among medium-volume hospitals and surgeons but superior outcomes for the highest volume surgeons and centers. However, the differences in outcomes based on volume are modest compared with other higher risk surgical procedures.
The increased national focus on surgical volume has led to changes in practice patterns for some procedures in which outcomes are strongly associated with procedural volume.17–19 In one report of patients undergoing cardiovascular and cancer surgery from 1999 to 2008, Birkmeyer et al noted that the median hospital volume for all four cancer operations studied increased substantially over time. The increased volume was the result of a combination of market concentration of procedures to a smaller number of hospitals as well as an increase in the overall number of cases for some procedures. Importantly, increased hospital volume was associated with decreased mortality. For pancreatectomy, operative mortality declined by 19% and increased hospital volume accounted for two thirds of this reduction in mortality.17
For women with endometrial cancer undergoing hysterectomy, we noted similar trends with an increase in mean surgeon and hospital volume over time. Although there was a small increase in the overall number of patients treated per year, market concentration to a smaller number of gynecologic surgeons and hospitals had a greater effect on increasing the mean procedural volumes. Concentration of endometrial cancer to a smaller number of surgeons and centers is likely driven by multiple factors. The increased complexity of treatment for endometrial cancer has resulted in fewer general gynecologists treating these women and professional societies now recommend referral of women with endometrial cancer to gynecologic oncology subspecialists.20 In one sample of women who underwent hysterectomy in 2014–2015, gynecologic oncologists provided care to more than 90% of the patients.8
These data demonstrate that the association between surgeon and hospital volume and outcomes for endometrial cancer is complex. The overall morbidity rate was higher for intermediate-volume surgeons and hospitals compared with low-volume health care providers but was the lowest for the highest volume surgeons and hospitals. However, in a multivariable analysis modeling surgeon and hospital volume as continuous variables, there was no association between surgeon volume and complications, whereas mortality was higher among high-volume surgeons. In contrast, mortality declined with increasing hospital volume, but complication rates were higher at high-volume hospitals.
These findings are likely driven by several factors. First, among low-volume surgeons, many hysterectomies for endometrial cancer were likely very early tumors or cases in which endometrial cancer was incidentally identified. These cases were likely technically less complex and thus associated with good outcomes. Morbidity was higher in the intermediate-volume strata but then decreased for the highest volume health care providers, perhaps reflecting an effect of volume on outcomes for these patients. Second, prior work has consistently shown that the volume–outcome paradigm is most pronounced for high-risk procedures that are associated with significant morbidity. For moderate-risk procedures, the effect of volume is often much smaller.21–23 Our findings are similar; the magnitude of association between volume and outcomes we found was small. Importantly, as in other studies of hysterectomy, we noted that increased surgeon volume was associated with decreased resource utilization, including hospital charges.14,23 These findings highlight the methodologic complexity of analyzing surgical volume for endometrial cancer.
Although our study benefits from the inclusion of a large sample of patients, we recognize a number of important limitations. First, we lacked data on tumor characteristics such as stage, histology, and uterine size that undoubtedly influenced treatment planning and outcome. To mitigate this bias, we adjusted for the performance of concomitant surgical procedures including lymphadenectomy and cytoreduction that are surrogates for extent of disease. Second, Statewide Planning and Research Cooperative System data are limited to patients in New York State and the findings we documented may not be representative of other areas in the United States. Third, although the Statewide Planning and Research Cooperative System has been widely used in prior work, there may be misclassification of covariates, outcomes, or surgeons in a small number of cases. Finally, although we examined short-term outcomes, we are unable to assess downstream care and long-term outcomes and quality of life.
From a policy perspective, these data suggest that surgeon and hospital volume are of limited value as quality metrics for endometrial cancer. Given prior work demonstrating a more robust association between surgical specialty and outcomes, efforts to direct the surgical care of women with endometrial cancer to gynecologic oncologists may be of more utility.24 Future efforts to determine the association between surgeon and hospital characteristics and downstream survival and quality of life will be of great interest.
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