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Ann Thorac Surg 2005;79:212-216
© 2005 The Society of Thoracic Surgeons

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Original article: General thoracic

National Trends in Outcomes for Esophageal Resection

Department of Surgery, University of Michigan Medical Center, Ann Arbor, Michigan, USA

Accepted for publication June 11, 2004.

^* Address reprint requests to Dr Dimick, 1500 E Medical Center Dr, Taubman Center 2210, Ann Arbor, MI 48109-0329 (E-mail: jdimick{at}umich.edu).

	Abstract

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BACKGROUND: Case-series reports from tertiary centers report improved outcomes for esophageal resection in recent years. The objective of the current study was to determine trends in short-term outcomes after esophageal resection in a representative sample of United States (US) hospitals.

METHODS: Observational study of all adult patients in the Nationwide Inpatient Sample who underwent esophageal resection from 1988 to 2000 (N = 8,657). Temporal trends of in-hospital mortality and prolonged length of stay were determined. Analyses were performed for all hospitals after stratifying by hospital volume. The proportion of patients having surgery at high volume hospitals was used to assess changes in referral patterns.

RESULTS: The overall mortality rate was 11.3% and revealed a modest but significant decline from 13.6% to 10.5% during the study period (p = 0.001). Low volume hospitals had markedly higher mortality rates and showed no improvement over time (15.3% vs 14.5%). In contrast, high volume hospitals indicated significant reduction in mortality over time (11.0% vs 7.5%, p = 0.003). Referral patterns changed over time with the proportion of esophageal resections performed at high volume hospitals increasing from 40% (1988 to 1991) to 57% (1997 to 2000).

CONCLUSIONS: The operative mortality rate for esophageal resection has declined over the past 13 years, particularly at high volume hospitals. Efforts should be made to understand the processes of care underlying this improvement.

	Introduction

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Esophageal resection has undergone several technical refinements over recent years, including increased utilization of the transhiatal approach to resection [1, 2]. Several case-series reports from centers with extensive experience with esophageal resection have demonstrated significant improvements in short-term outcomes [1, 2]. Little information exists regarding the outcomes from a population-based perspective.

Previous studies from state and national administrative datasets have demonstrated wide variation in operative mortality rates for esophageal resection [3–6]. Though several high-risk operations have a relationship of volume to outcome, esophageal resection is repeatedly shown to have the largest effect [4–6]. In fact, such studies show that low volume hospitals have operative mortality rates several-fold greater than high volume centers [3–6]. Given these differences among hospitals, it is not clear whether the improvements in outcomes reported from tertiary centers are occurring across all hospitals in the United States.

The current study was performed to determine trends over time in short-term outcomes after esophageal resection in a representative national sample of hospitals. Such data will determine whether the trends toward improved outcomes over time seen in high volume centers hold true in the general population. In addition, changes in referral patterns to high volume centers will be determined to establish the extent of regionalization that has occurred for this high-risk surgical procedure.

	Material and Methods

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Data Source
Patient data were derived from 13 years (1988 to 2000) of the Nationwide Inpatient Sample (NIS). This database is maintained by the Agency for Health Research and Quality (AHRQ) as part of the Healthcare Cost and Utilization Project (HCUP) [7]. The NIS is a 20% sample of all hospital discharges in the United States. The database is stratified by geographic region, hospital size, urban versus rural location, and teaching versus nonteaching in order to be a representative sample of all US hospitals.

Adult patients discharged from an NIS hospital from 1988 to 2000 with an international classification of diseases, ninth revision, clinical modification (ICD-9-CM) primary procedure code for esophageal resection were included for study (partial esophagectomy, ICD-9-CM code 42.41; total esophagectomy, ICD-9-CM code 42.42; and esophagectomy, not otherwise specified, ICD-9-CM code 42.40) [8]. Patient demographic information (age, race, gender), nature of admission (elective, urgent, emergent), in-hospital mortality, length of stay (LOS), and primary and secondary ICD-9-CM diagnostic codes were obtained from the NIS database. Coexisting diseases were determined using the secondary ICD-9-CM codes. The Romano modification of the Charlson comorbidity score was used to determine coexisting diseases from the ICD-9-CM codes [9–11].

Outcome Variables
The primary outcome variable was operative mortality (in-hospital mortality). We included prolonged length of stay (LOS) as a secondary outcome variable. LOS tends to have a right-skewed distribution and results are typically reported as difference in medians (or linear regression using log-transformed LOS). However, these analyses work to eliminate the effect of outliers. But in the case of high-risk surgery, these outliers are what we are interested in. Patients who are outliers for LOS experience complications, and such individuals are important to consider when determining outcomes of surgical care. We defined prolonged LOS a priori as a hospital stay of greater than the 75th percentile (24 days).

Hospital Volume
Each hospital included in the NIS has a unique hospital identification number that was used to calculate the number of esophageal resections performed for each year of the study period. Hospital volume thresholds were determined by dividing the patients into two equal-sized groups based on the median (50th percentile) hospital volume of 6 cases per year. The relationship between hospital volume and outcomes is continuous in nature and does not lend itself easily to creating a threshold. Thus, the median was used to define two equal sized groups and does not represent a threshold for referral.

Time Trends
To study the changes in outcomes and referral patterns over time, the study years were divided into three time periods as follows: time period 1 (1988 to 1991), time period 2 (1992 to 1996), and time period 3 (1997 to 2000). Changes in referral patterns were determined by comparing the proportion of patients having surgery at high volume centers during each time period.

Statistical Analysis
Univariate analyses were performed using ² test, Student's t test, and the Wilcoxon rank-sum test where appropriate. We used multiple logistic regression to conduct the risk-adjusted multivariate analysis for both operative mortality and prolonged LOS. Independent variables used for risk-adjustment included demographics (age, gender, race), indication for surgery (malignant vs benign), admission type (elective, urgent, or emergent), and coexisting diseases. Independent variables with p less than 0.1 in the univariate analysis were included in the multivariate analysis. The multivariate models were tested for goodness of fit using the Hosmer-Lemeshow test, and the area under the receiver operating characteristic (ROC) curve was calculated [12]. All statistical analyses were performed using STATA 7.0 (College Station, TX); p values less than 0.05 were considered significant in all final analyses.

	Results

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Patient Characteristics
During the 13-year study period there were 8,657 patients who underwent esophageal resection in the hospitals included in the NIS. Patients were generally similar across time periods with respect to age, gender, race, and coexisting diseases (Table 1). There was a significant decline in the number of patients with urgent (12% to 8%) and emergent admission (18% to 10%; p < 0.001). The dominant payer across all periods was Medicare (46% to 49%) followed by private insurance (37% to 43%) with no significant change over time. Median income increased with a smaller proportion of patients in the lowest category (p < 0.001; Table 1).

View larger version (76K): [in this window] [in a new window]   Fig 1. In-hospital mortality rates after esophageal resection for high and low volume hospitals across three time periods. There was a significant reduction in mortality at high volume hospitals but no reduction at low volume hospitals. = low volume; = high volume.

View larger version (50K): [in this window] [in a new window]   Fig 2. The proportion of patients having esophageal resection at high volume centers during three time periods in the United States. Each time period shows a progressive increase in the proportion of esophageal resections performed at high volume centers.

Length of Stay
The median length of stay (LOS) for patient having esophageal resection during the entire study period was 15 days (interquartile range [IQR], 11 to 24 days). Median LOS decreased over time from 17 days (IQR, 13 to 28 days) during 1988 to 1991 to 13 days (IQR 10 to 21 days) during 1997 to 2000 (p < 0.001). In addition, the proportion of patients experiencing prolonged LOS (greater than the 75th percentile) showed a significant decline from 33% during 1988 to 1991% to 21% during 1997 to 2000 (p < 0.001). When considering hospital volume, both high (33% to 20%, p < 0.001) and low volume hospitals (33% to 23%, p < 0.001) showed a decline in the proportion of patients with prolonged LOS (Fig 3). In the risk-adjusted multivariate analysis, there was a significant reduction in prolonged LOS for both time period 2 (OR, 0.73; 95% CI, 0.61–0.88) and time period 3 (OR, 0.59; 95% CI, 0.49–0.71) compared to the first time period.

View larger version (67K): [in this window] [in a new window]   Fig 3. Proportion of patients with prolonged length of stay after esophageal resection for high and low volume hospitals across three time periods. There was a significant reduction over time for both low and high volume hospitals. = low volume; = high volume.

	Comment

Top Abstract Introduction Material and Methods Results Comment References

Our findings are in contrast to a previous study by Goodney and colleagues [13]. The authors studied trends in operative mortality for several surgical procedures, including esophagectomy for cancer, from 1994 to 1999. For esophageal resection, they found no significant changes in mortality over that time period. Although the patient populations differ to some degree (100% Medicare vs 20% of all-payer admissions), the most likely factor causing the different findings is the time horizon. Our study went back several more years than the study by Goodney and colleagues [13]. Indeed, when examining our results, our study also found no significant decline from our time period 2 (1992 to 1996) to time period 3 (1997 to 2000). However, we did find a significant decline, particularly for high volume hospitals from time period 1 (1998 to 1991) to time period 2 (1992 to 1996). Thus, the reduction we observed in our study predated the time interval included in this previous study conducted in the Medicare population.

The information presented in our current study has important implications regarding operative risk for esophageal resection in US hospitals. Clinical information regarding outcomes of surgical procedures is most often derived from clinical case-series from tertiary centers of excellence. In general, the results reported in such studies do not reflect the results at most other hospitals. Indeed, the high volume centers in the present study (>6 cases per year) still have a mortality rate much greater than the hospitals that report the best outcomes [1, 2]. Most of the previous volume-outcome literature has used a cut-off in this same range (6 to 7 per year) and demonstrated a significant difference in mortality between high and low volume hospitals. However, while referring patients to hospitals that perform above this threshold will, on average, result in lower mortality rates, it is important to remember that this number does not define the optimal threshold for referral—instead it represents an arbitrary cut-off established a priori for the purpose of demonstrating variation in mortality rates across hospitals.

The discrepancy between outcomes reported in case-series and population-based studies have profound implications regarding informing patients of operative risk. Without information regarding the volume of cases performed, patients cannot be adequately informed regarding the risk of operation. Given the wide variations in outcome for esophageal resection, the risk of mortality may change patient's decision to undergo surgery. Or alternatively, they may wish to be referred to a medical center with more experience with the operation.

Despite limitations, provider volume has become a surrogate for the quality of surgical care among hospitals. Many critics of volume-based referral argue that measuring outcomes directly may be a more viable option for assessing the quality after complex surgical procedures such as esophageal resection. However, given the small numbers of procedures performed at single hospitals, direct outcomes measurement is not an option for esophageal surgery. In contrast to cardiac surgery, where a given hospital performs hundreds of procedures per year, most hospitals performing esophageal surgery only treat a handful of patients per year.

With the large numbers of patients undergoing cardiac surgery, it is feasible to measure and compare risk-adjusted outcomes. Several regional efforts have demonstrated the effectiveness of using risk-adjusted outcomes data for quality improvement in cardiac surgery [14, 15]. Additionally, the Veterans Affairs system has used outcomes data for noncardiac surgery but relies on a mortality measure that combines multiple surgical procedures [16]. It is not known if a summary mortality measure, one created by combining several operations, adequately represents the quality of individual surgical procedures. For example, a certain hospital may have an "overall" high quality rating but only perform hernia repairs and colon resections. Would that hospital be considered high quality for esophageal resections as well? The relative utility of summary quality measures and information on procedural volume requires further investigation.

The current study was conducted using an administrative database and is subject to certain limitations. Specifically, the ability to adjust for differing severity of illness and coexisting diseases is limited. In the present study, the case-mix adjustment included demographics (age, gender, race), nature of admission (elective, urgent, emergent), primary diagnosis, and several coexisting diseases. Using a clinical database with more clinical and physiologic variables would provide for more robust risk adjustment. However, the profound effect of volume on outcome for esophageal resection is unlikely to be affected significantly by such adjustment. Previously, there did not exist a nationally representative clinical database for general thoracic surgical procedures. However, currently the Society of Thoracic Surgeons database is expanding to include general thoracic procedures. The database used for the current study, the Nationwide Inpatient Sample, is a 20% sample of US hospitals stratified by geographic region, hospital size, urban versus rural location, and teaching status. Therefore, using the NIS will yield a generalizable estimate of changes in short-term outcomes over time.

The current study demonstrates that there has been a modest decline in operative mortality after esophageal resection in a nationally representative sample of hospitals. Further, it appears that the improvement in mortality is limited to high volume hospitals. There has also been significant change in referral patterns over the same time period with the proportion of esophageal resections performed at high volume hospitals increasing during the study period. Despite these changes, there are a large proportion of patients still having surgery at low volume centers. Further concentration of this complex procedure in high volume centers will continue to improve overall outcomes.

	References

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