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Ann Thorac Surg 2003;75:337-341
© 2003 The Society of Thoracic Surgeons

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Original article: general thoracic

Surgical volume and quality of care for esophageal resection: do high-volume hospitals have fewer complications?

^a Department of Surgery, the University of Michigan Medical Center, Ann Arbor, Michigan, USA
^b Department of Surgery, The Johns Hopkins Medical Institutions, Baltimore, Maryland, USA

Accepted for publication September 5, 2002.

* Address reprint requests to Dr Lipsett, Department of Surgery, The Johns Hopkins Hospital, 600 N Wolfe Street, Blalock 685, Baltimore, MD 21287-4685, USA
e-mail: plipsett{at}jhmi.edu

	Abstract

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BACKGROUND: Previous studies have shown that high-volume hospitals (HVHs) have lower mortality rates than low-volume hospitals (LVHs). However, little is known regarding the relationship of morbidity to hospital volume. The objective of the current study was to investigate the relative incidence of postoperative complications after esophageal resection at HVHs and LVHs.

METHODS: All patients discharged from a nonfederal, acute-care hospital in Maryland after esophageal resection from 1994 to 1998 were included (n = 366). Rates of 10 postoperative complications were compared at HVHs and LVHs. Risk-adjusted analyses were performed using multiple logistic regression.

RESULTS: High-volume hospitals had a mortality rate of 2.5% compared with 15.4% at LVHs (p < 0.001), with a case-mixed adjusted odds ratio (OR) of death equal to 5.7 (95% confidence interval [CI], 2.0 to 16; p < 0.001). Low-volume hospitals had a profound increase in the risk of several complications after adjusting for case-mix: renal failure (OR, 19; 95% CI, 1.9 to 178; p = 0.01), pulmonary failure (OR, 4.8; 95% CI, 1.6 to 14; p = 0.002), septicemia (OR, 4.0; 95% CI, 1.1 to 15; p = 0.04), reintubation (OR, 2.9; 95% CI, 1.4 to 6.1; p = 0.004), surgical complications (OR, 3.3; 95% CI, 1.6 to 6.9; p = 0.001), and aspiration (OR, 1.8; 95% CI, 1.0 to 3.3; p = 0.04).

CONCLUSIONS: Patients undergoing esophageal resection at LVHs were at a markedly increased risk of postoperative complications and death. Pulmonary complications are particularly prevalent at LVHs and contribute to the death of patients having surgery at those centers.

	Introduction

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Esophageal resection is a complex, high-risk surgical procedure, which is performed in a variety of hospitals across the United States. Several previous population-based studies have demonstrated that high-volume hospitals (HVHs) have superior outcomes compared with low-volume hospitals (LVHs) [1–9]. Although health policy has focused on concentrating esophageal surgery in high-volume settings, many patients are still undergoing the operation at LVHs [10, 11].

Recent attention has focused on the gap between the quality of care patients receive and the quality the health care system in the United States is capable of providing [12]. Surgical volume can be considered a surrogate for quality of care, because HVHs consistently have lower mortality rates after several surgical procedures. Postoperative complications vary between medical centers and can be considered an indicator of poor quality for surgical procedures [13–16]. The objective of the current study was to determine the relationship of provider volume to postoperative complications after esophageal resection.

	Material and methods

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Data source
Nonconfidential patient data from the Uniform Health Discharge Data Set maintained by the Maryland Health Services Cost Review Commission (HSCRC) was used for patient information and clinical and economic outcomes. This database contains information on all patients discharged from 52 nonfederal acute-care hospitals in the state of Maryland. Using the database, we abstracted patient age, sex, race, nature of admission, operating physician, vital status at discharge, total hospital, and intensive care unit length of stay, and codes from the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) for the primary discharge diagnosis, the principal procedure, and up to 14 secondary diagnostic and procedure codes [17]. The study included adult patients discharged from a Maryland hospital between January 1994 and December 1998 with a primary procedure code for esophageal resection (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).

Postoperative complications
Information on complications was taken from secondary ICD-9-CM codes available in the HSCRC database. The complications were as follows: aspiration (ICD-9-CM codes 507 and 9973); pulmonary insufficiency (ICD-9-CM codes 5184, 5185 and 5188); cardiac complications (ICD-9-CM code 9971); pneumonia (ICD-9-CM codes 480 to 487); acute renal failure (ICD-9-CM code 584); septicemia (ICD-9-CM code 038); postoperative infection (ICD-9-CM code 9985); cardiac arrest (ICD-9-CM code 4275); acute myocardial infarction (ICD-9-CM code 410); reintubation (ICD-9-CM code 9604); reoperation for bleeding (ICD-9-CM codes 3941, 3949, and 3998); and surgical complications after a procedure (ICD-9-CM codes 9981, 9982, and 9983).

For previous work using this database, hospital charts of several patients were reviewed to ensure the accuracy of coding for the selected complications; the charts were found to be 96% accurate [18]. Furthermore, in a recent investigation, the authors demonstrated the validity of ICD-9-CM coding of several medical and surgical complications [15]. The positive predictive value for included complications varied from 84.2% to 96.8% with kappa scores of 0.69 (good agreement) to 0.88 (excellent agreement) when comparing ICD-9-CM coding and the clinical record [15, 16]. Finally, several complications were not included in our analysis, primarily complications that are not well represented by ICD-9-CM coding. One particular relevant complication of esophageal resection, anastomotic leak, does not have a specific ICD-9-CM code. However, the codes for "surgical complications" are inclusive and likely include anastomotic failure. Also, any unrepresented complication will likely place the patient at risk for other complications (eg, sepsis, aspiration) and will be reflected in the overall quality of care for the patient.

Risk adjustment
Comorbid disease was adjusted for using Romano’s modification of the Charlson comorbidity index for use with ICD-9-CM discharge codes from an index hospitalization [19–21]. For the severity of illness adjustment, we used the nature of admission field assigned at the time of admission (elective, urgent, or emergent) and the operative procedure was classified as partial (ICD-9-CM code 42.41), complete (ICD-9-CM code 42.42), or not specified (ICD-9-CM code 42.40) esophagectomy.

Statistical analysis
The threshold for hospital volume was chosen as the inflection point (increase in mortality rate) of the volume versus mortality curve after applying a Lowess smoothing function [22]. Hospital volume was converted into dichotomous variables using a threshold for "low" and "high" volume. The actual threshold for hospital volume was 34 cases during the study period. This threshold is consistent with current health policy initiatives suggesting regionalization of esophageal resection [10, 11]. Tests of univariate association were performed using the ² test, simple logistic regression, t test, Wilcoxon rank-sum, and simple linear regression where appropriate. The multivariate model of mortality was performed using multiple logistic regression and included all covariates with p less than 0.2 in univariate analysis. To calculate adjusted odds ratios (OR) and 95% confidence intervals (CI) for each complication, a separate logistic regression model was constructed using each postoperative complication as the dependent variable. All univariate predictors with p less than 0.2 for each complication were included in the multivariate model. All analyses were performed with STATA 6.0 (Houston, TX).

	Results

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Patient demographics
From 1994 to 1998, 366 adult patients had primary procedure codes for esophageal resection in the Maryland HSCRC database. There were two HVHs and 33 LVHs in the sample, with 19%of patients undergoing surgery at hospitals that performed at most one resection per year and 30% of patients undergoing surgery at hospitals that performed two or fewer per year. Patients who underwent esophagectomy had ICD-9-CM primary diagnoses of esophageal malignancy (64%); stomach malignancy, predominantly of the cardia (16%); benign esophageal disease (15%); traumatic esophageal injury (2%); or other disease (2%). Patients at LVHs and HVHs were generally similar according to demographics and comorbid disease, with a few notable differences (Table 1). Patients at LVHs were more likely to be of nonwhite race, have urgent or emergent admission, or have a history of chronic pulmonary disease (Table 1).

Several complications were predictive of in-hospital mortality after esophageal resection. The significant complications included pulmonary failure (OR, 6.8. 95% CI, 2.7 to 17.5), renal failure (OR, 41.5. 95% CI, 11.9 to 144), pneumonia (OR, 2.7. 95% CI, 1.1 to 6.8), postoperative infection (OR, 3.8. 95% CI, 1.2 to 12.6), reintubation (OR, 5.7. 95% CI, 2.6 to 12.4), and septicemia (OR, 8.2. 95% CI, 2.5 to 26.9).

Complications and hospital volume
The overall complication rate was 43%, with 22% of patients having one complication, 11% having two complications, 4% having three complications, and 5% having four or more complications. The mortality rate was significantly associated with an increasing number of complications. Mortality was 6.2% for patients with at most one complication compared with 16.0% for patients with two or more complications (p = 0.006). Compared with HVHs, having surgery at an LVH was associated with a higher incidence of several complications (Table 2, Fig 1). The risk of developing several complications based on hospital volume is shown in Table 3. In the adjusted model, taking into account differences in patient characteristics, the magnitude of the effect was altered the same complications were still significant (Table 3).

View larger version (18K): [in this window] [in a new window]   Fig 1. Frequency of postoperative complications at high- and low-volume hospitals after esophageal resection in Maryland, 1994 to 1998. = low-volume hospitals; = high-volume hospitals. *p < 0.05.

	Comment

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Esophageal resection is performed in a variety of settings across the United States. In some geographic regions and certain medical centers, thoracic surgeons who have received advanced training perform esophageal operations exclusively. General surgeons, who have received a variable amount of training in thoracic procedures, also perform esophagectomy. It is unclear to what extent subspecialty training affects the outcomes of this high-risk procedure. However, hospitals that perform high volumes of esophageal operations have clearly superior outcomes [1–9]. This effect of volume on outcome has been demonstrated for almost every complex surgical procedure [1, 23]. The magnitude of the effect, however, is consistently large for esophageal resection [1–9, 23]. For example, in a recent report from the national Medicare database Birkmeyer and colleagues [1] reported a mortality rate of 20.3% for very low-volume centers (fewer than two esophageal operations per year) compared with 8.4% for very high-volume centers (more than 19 esophageal operations per year). The overall higher mortality rate for the present study was attributable to the increased age of the Medicare population compared with statewide databases, which include patients of all ages. Such reports from Maryland, Massachusetts, and California have shown a similar effect of hospital volume on outcome for this operation [3, 4, 6].

Volume is a surrogate of quality for complex surgical procedures, particularly esophageal resection. Hospital volume is a generic variable that likely represents a complex system of independent contributing structure and process variables that relate to patient care. This system must include preoperative selection and optimization, intraoperative technical proficiency and appropriate resuscitation, and postoperative prevention and treatment of complications. For instance, previous data have shown that having daily rounds by an intensive care physician and appropriate nurse staffing are related to outcomes after esophageal resection [24, 25]. Further research is needed to identify other structure and process variables that lead to improved outcomes at high-volume centers.

The current study was based on administrative data and is therefore subject to certain limitations. Patient comorbid disease and complications were taken from secondary ICD-9-CM codes and therefore their data are not as accurate as those from a prospective clinical database. However, using hospital discharge data allows for the complete and unbiased assessment of outcomes across all hospitals in the state of Maryland. Such a project would be unfeasible using clinical data. Using a physiologic risk adjustment score would add to our ability to adjust for severity of illness, especially for patients with urgent or emergent admission. In our analysis, when considering elective cases only, the mortality rate was 3.2% at HVHs compared with 11.5% at LVHs (p = 0.005). Furthermore, the multivariate analysis takes into account measurable differences in the patient groups. Given the profound effect of volume on outcome for both mortality and complications (several-fold increase in risk), it is highly unlikely that this difference is a result of unmeasured differences in case-mix.

In conclusion, the current study demonstrates that patients who undergo esophageal surgery at an LVH are at markedly increased risk of several important postoperative complications. These complications can lead to mortality and suggest that the mode of death at LVHs is related, in many cases, to pulmonary or other medical complications. Increased provider volume is therefore both a marker of lower mortality and fewer complications. Patients in need of esophageal surgery should seek referral to an HVH. Currently, procedural volume may be the best marker of quality available for esophageal resection.

	References

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