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Obstetrics & Gynecology:
doi: 10.1097/AOG.0b013e318248f7a8
Original Research

Effect of Surgical Volume on Outcomes for Laparoscopic Hysterectomy for Benign Indications

Wallenstein, Michelle R. MD; Ananth, Cande V. PhD, MPH; Kim, Jin Hee MD; Burke, William M. MD; Hershman, Dawn L. MD; Lewin, Sharyn N. MD; Neugut, Alfred I. MD, PhD; Lu, Yu-Shiang MS; Herzog, Thomas J. MD; Wright, Jason D. MD

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Author Information

From the Departments of Obstetrics and Gynecology and Medicine, Columbia University College of Physicians and Surgeons, the Department of Epidemiology, Mailman School of Public Health, and the Herbert Irving Comprehensive Cancer Center, New York, New York.

See related editorial on page 693 and related article on page 700.

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 Ave, 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 influence of surgical volume on outcome and resource utilization for laparoscopic hysterectomy for benign indications.

METHODS: Patients who underwent laparoscopic hysterectomy from 2000 to 2010 and recorded in a commercial database were analyzed. Patients were stratified into tertiles according to the number of procedures performed by their surgeons and at their hospital. The influence of surgeon and hospital volume on perioperative morbidity and resource utilization was examined using multivariable regression models.

RESULTS: A total of 124,615 patients were identified. The overall complication rate decreased from 6.2% for low-volume surgeons to 4.2% for high-volume surgeons (P<.001). Patients operated on by high-volume surgeons were 25% (risk ratios [RRs] 0.75, 95% confidence interval [CI] 0.68–0.82) less likely to experience a complication. In multivariable models intraoperative complications, surgical-site complications, medical complications, prolonged hospitalization, and transfusion rates were lower for high-volume surgeons. Overall morbidity was 5.8% for women treated at low-volume hospitals compared with 4.7% at high-volume centers (P<.001). Women treated at high-volume centers were 18% (RR 0.82, 95% CI 0.75–0.90) less likely to experience a complication. Procedure costs for high-volume surgeons were $867 lower than for low-volume surgeons, and treatment at a high-volume center reduced costs by $966 per procedure.

CONCLUSION: Performance of laparoscopic hysterectomy by high-volume surgeons and at high-volume hospitals is associated with modest reductions in morbidity and lower costs.

LEVEL OF EVIDENCE: II

Approximately 600,000 women undergo hysterectomy each year in the United States, making hysterectomy the most common major gynecologic surgery in this country.1 Although the rate of abdominal hysterectomy has been decreasing, this remains the most common route for the procedure.2 When clinically feasible, approaches for removal of the uterus that result in less morbidity, such as either vaginal or laparoscopic hysterectomy, are preferred.3 The proportion of hysterectomies performed laparoscopically is increasing and has risen from 0.3% in 1990 to 11.8% in 2003.2

Laparoscopic hysterectomy offers a number of advantages over open hysterectomy including shorter recovery times, lower blood loss, and decreased infectious morbidity. In contrast, the laparoscopic procedure typically is associated with longer operative times and is accompanied by a higher rate of intraoperative injury to the urinary tract.3 For surgical procedures there is now growing recognition that in addition to patient factors, both physician and hospital characteristics influence the care a patient receives as well as outcomes.4,5 One of the most important surgeon and systems characteristics is surgical volume. For many procedures, patients treated by high-volume surgeons and in high-volume centers have superior outcomes compared with patients operated on by lower-volume providers.48 The volume-outcome paradigm has a major effect on outcomes for high-risk cancer and cardiovascular procedures.4,5,7

Relatively little is known about the effect of surgical volume on outcome for laparoscopic hysterectomy.9,10 Laparoscopic hysterectomy is technically demanding, a relatively new procedure, and an operation that is still performed relatively infrequently by many gynecologists. All of these factors suggest that surgical volume may influence outcomes of laparoscopic hysterectomy. The objective of our study was to estimate the influence of surgeon and hospital volume on perioperative morbidity, mortality, and resource utilization for women undergoing laparoscopic hysterectomy for benign indications.

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MATERIALS AND METHODS

Data from the Perspective (Premier) database were analyzed. Perspective is a nationwide, all-payer, voluntary, fee-supported database developed to measure healthcare quality and resource utilization. Perspective collects inpatient data from more than 500 acute-care hospitals throughout the United States. The database is updated quarterly and undergoes a rigorous auditing process to ensure quality and integrity. Perspective collects data on patient demographics, clinical characteristics, and all billed services. In 2006 Perspective recorded approximately 5.5 million hospital discharges that represent approximately 15% of nationwide hospitalizations.11,12 The study was approved by the Columbia University Institutional Review Board.

Women who underwent laparoscopic hysterectomy billed as a total laparoscopic hysterectomy (International Classification of Diseases, 9th Revision [ICD-9] 68.41) or laparoscopically assisted vaginal hysterectomy (ICD-9 68.51) between 2000 and 2010 were analyzed. A priori patients with a diagnosis of a pelvic malignancy or those who underwent a primary open, vaginal, robotic, or radical hysterectomy were excluded from analysis. Indications for surgery including leiomyoma, endometriosis, bleeding, ovarian mass, and pelvic organ prolapse were recorded for each patient. Other ancillary procedures that may have been performed at the time of hysterectomy including oophorectomy, anterior colporrhaphy, posterior colporrhaphy, and anti-incontinence surgery were also noted for each patient.

Demographic data that were analyzed included age (younger than 40, 40–60, older than 60 years), year of diagnosis (2000–2006, 2007–2010), race (white, African American, other), marital status (married, single, unknown), and insurance status (Medicare, Medicaid, commercial, self pay, unknown). The hospitals in which patients were treated were characterized based on location (urban, rural), region of the country (northeast, midwest, west, south), size (fewer than 400 beds, 400–600 beds, more than 600 beds), and teaching status (teaching, nonteaching). Risk adjustment for comorbid conditions was performed using the Charlson comorbidity index.13 The ICD-9 coding to define the Charlson index as reported by Deyo and colleagues was used.14

The volume of each patient's treating surgeon and hospital were calculated. Considering that not all surgeons contributed patients during the entire study period, we calculated annualized volume by dividing the total number of procedures performed by the number of years in which an individual surgeon performed at least one laparoscopic hysterectomy. A similar classification schema for annualized hospital volume was used. Surgeon and hospital volume cutpoints were then selected to divide patients into approximately equal volume-based tertiles: low, intermediate, and high, as has been previously reported.15,16

The primary endpoints of the study were perioperative morbidity and resource utilization. Complications were assessed using billed ICD-9 codes and categorized into the following groups: 1) operative complications (bladder injury, ureteral injury, intestinal injury, vascular injury, other operative injury), 2) surgical-site complications (postoperative hemorrhage, wound complications, abscess, bowel obstruction, ileus), and 3) medical complications (venous thromboembolism, myocardial infarction, cardiopulmonary arrest, respiratory failure, renal failure, stroke, bacteremia or sepsis or both, shock, pneumonia). A composite score of overall morbidity was determined based on the occurrence of any one of the above complications in a patient.

Length of hospital stay was defined as the number of days from the procedure until discharge. A prolonged hospitalization was defined as longer than 2 days. Rates of transfusion and reoperation were calculated. Cost was analyzed using a calculation of all patient costs. Within the Perspectives database approximately three quarters of hospitals submit direct cost data taken from internal accounting systems, and the remaining institutions provide estimates based on Medicare cost-to-charge ratios.11,12,17 Hospital costs were adjusted for inflation using the Consumer Price Index and reported in 2010 U.S. dollars.18 The discharge status of each patient was recorded. Nonroutine discharge was defined as transfer to a skilled nursing facility, nursing home, or acute or subacute rehabilitation center. Perioperative death was defined as death during the hospitalization during which the patient underwent the procedure.

Frequency distributions between categorical variables were compared using χ2 tests, and continuous variables were compared using a one-way analysis of variance. To account for hospital and surgeon clusters, we used multivariate mixed-effects logistic regression models.19 Sensitivity analyses were initially performed on two separate models by allowing surgeons and hospitals as random intercepts. These analyses demonstrated little variability across hospitals and therefore the final models included only a random intercept for surgeons. All of the models include patient, surgeon, and hospital characteristics as well as a random intercept for surgeons. Results are reported as risk ratios (RRs) with 95% confidence intervals (CIs). Median costs were estimated for each physician and hospital tertile and reported with interquartile ranges. All analyses were performed with SAS 9.2.

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RESULTS

A total of 124,615 patients underwent laparoscopic hysterectomy for benign conditions by 7,925 surgeons at 534 hospitals across the United States. Low-volume surgeons (fewer than 5.88 procedures per year) operated on 41,531, and high-volume surgeons (more than 14.10 operations per year) treated 41,542 women. Low-volume hospitals performed fewer than 49.4 procedures per year, intermediate-volume hospitals 46.4–105 procedures per year, and high-volume hospitals more than 105 laparoscopic hysterectomies per year (Table 1).

Table 1
Table 1
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Table 1 displays the clinical and demographic characteristics of the cohort. Compared with patients operated on by low-volume surgeons, those women treated by high-volume surgeons were more likely to be younger, were more often white, were more likely to have Medicare, more frequently resided in the south or midwest regions of the United States, and had fewer medical comorbidities (P<.001 for all). High-volume surgeons were more likely to operate at nonteaching hospitals and at smaller hospitals (P<.001 for all). In comparison with the years 2000–2006, patients who underwent operations in 2007–2010 were more likely to be operated on by a low-volume surgeon (P<.001). Compared with patients operated on at low-volume hospitals, those women operated on at high-volume hospitals were more likely to be white, were younger, more often had commercial insurance, and more frequently resided in the southern United States (P<.001 for all).

The overall complication rate was 6.2% (n=2,565) for low-volume surgeons, 5.2% (n=2,149) for intermediate-volume surgeons, and 4.2% (n=1,762) for high-volume surgeons (P<.001) (Table 2 and Fig. 1). Each of the individual complications classes including intraoperative injuries, surgical-site complications, medical complications, and transfusion decreased with increased surgeon volume. Hospitalization for longer than 2 days was required in 9.6% of patients treated by low-volume surgeons compared with 6.3% of women operated on by high-volume surgeons (P<.001). There were no differences in nonroutine discharge or perioperative mortality across the volume strata.

Table 2
Table 2
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Fig. 1
Fig. 1
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The complication rate decreased from 5.8% (n=2,440) at low-volume hospitals to 5.0% (n=2,077) at intermediate-volume hospitals and to 4.7% (n=1,959) at high-volume facilities (P<.001) (Table 3 and Fig. 1). Treatment at high-volume hospitals was associated with reductions in intraoperative complications (P=.007), surgical-site complications (P<.001), and medical complications (P<.001). Transfusions (P<.001) and prolonged hospitalization (P<.001) were more common at low-volume centers. Nonroutine discharges were noted for 0.3% (n=108) of women at low-volume and for 0.1% (n=44) of patients at high-volume centers. Whereas nonroutine discharge was more common at low-volume hospitals, there was no difference in mortality across the volume strata.

Table 3
Table 3
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In the multivariable analysis, risks of overall morbidity (RR 0.75, 95% CI 0.68–0.82), intraoperative complications (RR 0.85, 95% CI 0.74–0.96), surgical-site complications (RR 0.70, 95% CI 0.60–0.82), medical complications (RR 0.63, 95% CI 0.53–0.76), transfusion (RR 0.75, 95% CI 0.61–0.93), and prolonged hospitalization (RR 0.65, 95% CI 0.58–0.74) were all reduced when the procedure was performed by a high-volume surgeon (Table 4). Likewise, risks of overall morbidity (RR 0.82, 95% CI 0.75–0.90), intraoperative complications (RR 0.83, 95% CI 0.73–0.94), surgical-site complications (RR 0.78, 95% CI 0.68–0.90), transfusion (RR 0.52, 95% CI 0.43–0.63), and prolonged hospitalization (RR 0.61, 95% CI 0.55–0.67) were reduced when patients were operated on at high-volume hospitals.

Table 4
Table 4
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Resource utilization was then examined. The median cost of procedures performed by low-volume surgeons was $6,390 and decreased to $5,523 for high-volume surgeons (P<.001). The average cost of laparoscopic hysterectomy undertaken at low-volume hospitals was $6,527 compared with $5,561 at high-volume hospitals (P<.001).

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DISCUSSION

Our findings suggest that both hospital and surgeon volume have a clinically modest but statistically significant effect on perioperative outcomes for women undergoing laparoscopic hysterectomy for benign gynecologic conditions. Women treated by high-volume surgeons and at high-volume hospitals have lower morbidity. Surgical volume also has a direct effect on lowering resource utilization.

Studies examining the influence of surgical volume on outcomes for gynecologic surgery have reported mixed results.9,10,15,16,2027 A study examining hysterectomy performed by all routes for benign disease in New York State noted that short-term morbidity and mortality were lower when the procedure was performed by a high-volume surgeon.10 For women undergoing hysterectomy for endometrial cancer it has also been reported that patients operated on by high-volume surgeons have superior outcomes.16,20 Finally, our group previously examined the effect of volume on outcomes specifically for vaginal hysterectomy and noted that higher surgeon volume was associated with decreased perioperative complications and lower resource utilization.15

Data specifically examining the effect of volume on outcomes for laparoscopic hysterectomy have been limited. In an institutional series of 1,016 laparoscopic hysterectomies, Tunitsky and colleagues found that low-volume surgeons had longer operative times but there was no difference in perioperative morbidity.9 These authors noted that operative times and conversion rates decreased among the high-volume surgeons as their procedural experience increased. In addition to outcomes, surgical volume appears to exert an influence on access to laparoscopy. A population-based analysis of patients undergoing sigmoid resection noted that patients treated by high-volume surgeons were 8.8 times more likely to undergo a laparoscopic procedure than those managed by low-volume providers.28 Likewise, Boyd and colleagues reported that surgeons who perform at least 10 hysterectomies a year are more likely to perform a minimally invasive procedure than their lower-volume counterparts.10

Compared with procedures with more substantial perioperative morbidity, the effect of volume on outcomes in our sample was modest. These findings are in accord with other studies that have examined the influence of volume on outcomes for intermediate-risk surgeries.29 Data from the National Surgical Quality Improvement Program that evaluated eight intermediate-complexity operations found no association between volume and perioperative mortality.29 To place our findings into context, a recent meta-analysis reported that only 13 pancreatectomies would need to be moved from a low-volume hospital to a hospital with an upper quartile of volume to prevent one volume-associated death.7 In our cohort, 58 patients would need to be moved from a low- to a high-volume provider to prevent one complication. Perhaps more important than the effect of volume on morbidity were our findings that procedures performed by lower-volume surgeons and low-volume centers were consistently more costly. If one conservatively assumes that 550,000 hysterectomies are performed annually for benign disease and that 15% of the procedures are laparoscopic, replicating the outcomes of high-volume surgeons would reduce nationwide costs by more than $71.5 million, and the outcomes achieved at high-volume hospitals would lead to $79.7 million in cost savings.

Although our work benefits from the inclusion of a large number of women who underwent laparoscopic hysterectomy, we acknowledge a number of limitations. Complications are underreported in administrative data. To mitigate this limitation we analyzed only major perioperative complications that likely would generate a claim. Underreporting of complications should have been equally distributed across the groups. The Perspective database lacks data on pathologic characteristics of the uteri removed as well as surgical history. It is well known that uterine size and weight and surgical history influence operative decision-making as well as morbidity. Finally, calculations of surgical volume are associated with some degree of imprecision. In our analysis we divided patients into tertiles based on annual surgical volume as has been described previously.30,31 These estimates are based on patients operated on at the hospitals included in the Perspectives data, and surgeon and hospital volume are not independent.

Our findings suggest that a greater number of women are undergoing surgery by lower-volume providers. Whereas 39% of women were treated by low-volume surgeons between 2000 and 2006, from 2007 to 2010 this number had increased to more than 50%. Whereas laparoscopic hysterectomy was initially performed by relatively few physicians, the majority of gynecology residents are now exposed to the procedure during training and perform the surgery in practice although their yearly procedural volume may be low. These ongoing trends may further widen the differences in resource utilization and morbidity we noted. Initiatives to overcome volume-associated disparities typically focus on either regionalization of care or quality improvement for low-volume providers. Given the frequency with which laparoscopic hysterectomy is performed, efforts to improve quality are clearly warranted. A number of initiatives including pay-for-performance programs, public reporting of outcomes, and increased training in minimally invasive surgery have been described. As the use of laparoscopic hysterectomy increases, efforts to monitor quality and improve patient outcomes are clearly warranted.

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