
a Harvard Pediatric Health Services Research Fellowship Program, Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts
b Department of Pediatrics, University of Utah, Primary Children's Medical Center, Salt Lake City, Utah
| ABSTRACT |
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METHODS. The authors conducted a retrospective cohort study using the Kids' Inpatient Database 1997 and 2000. Patients with HLHS undergoing stage I palliation were identified using International Classification of Diseases, Ninth Revision, Clinical Modification diagnostic and procedural codes.
RESULTS. Seven hundred fifty-four and 880 discharges of children with HLHS undergoing stage I palliation in 1997 and 2000, respectively, were identified. The in-hospital mortality for the study population was 28% in 1997 and 24% in 2000. Twenty percent of stage I palliation operations were performed in nonteaching hospitals in 1997. Two percent of operations were performed in nonteaching hospitals in 2000. In 1997 only, in-hospital mortality remained higher in nonteaching hospitals after controlling for stage I palliation hospital volume and condition-severity diagnoses. Low-volume hospitals performing stage I palliation were associated with increased in-hospital mortality in 1997 and 2000.
CONCLUSIONS. Patients with HLHS undergoing stage I palliation in nonteaching hospitals experienced increased in-hospital mortality in 1997. A significant reduction in the number of stage I palliation procedures performed in nonteaching hospitals occurred between 1997 and 2000. This centralization of stage I palliation into teaching hospitals, along with advances in postoperative medical and surgical care for these children, was associated with a decrease in mortality. Patients in low-volume hospitals performing stage I palliation continued to experience increased mortality in 2000.
Key Words: teaching hospital hypoplastic left heart syndrome mortality Kids Inpatient Database resource use
Abbreviations: HLHShypoplastic left heart syndrome KIDKids' Inpatient Database ICD-9-CMInternational Classification of Diseases, Ninth Revision, Clinical Modification AHAAmerican Hospital Association ORodds ratio CIconfidence interval IQRinterquartile range
Hypoplastic left heart syndrome (HLHS) is a rare, complex cardiac disease that requires immediate intensive care and urgent cardiovascular surgical intervention for long-term survival. HLHS is associated with a spectrum of cardiac anomalies, including mitral stenosis and atresia, aortic stenosis and atresia, aortic hypoplasia, and a small or absent left ventricle.1 Historically, pediatric patients with HLHS who are less than 1 year of age have experienced the highest mortality of all congenital heart defects.2
Treatment options for children with HLHS include staged surgical palliation, orthotopic heart transplantation, or comfort care.35 Most children with HLHS who engage in treatment undergo surgical palliation.6 Surgical palliation involves 3 stages. Classic stage I palliation involves the placement of a systemic to pulmonary shunt, creation or enhancement of an atrial septal defect, and creation of a neoaorta using the main pulmonary artery.7 An alternative approach to stage I palliation involving a right ventricle to pulmonary artery conduit has also emerged.8 Stage I palliation typically occurs shortly after birth, although premature or low-birth-weight infants may experience later operative dates to achieve more weight at surgery.
Operative survival for stage I palliation has improved over the last 2 decades, although results remain highly variable between institutions.914 National administrative database studies from the late 1990s suggest that operative mortality for stage I palliation is between 32% and 38%.6, 15 Individual centers report case series with operative mortality as low as 8% to 15%.12, 14 Prematurity,16 lower birth weight,17 lower weight at operation,13, 18 longer circulatory arrest time,19 restrictive atrial septal defect,16 ascending aortic diameter,20 aortic atresia,21 and chromosomal and noncardiac structural anomalies11, 18 have been associated with increased stage I palliation mortality.
Reduced mortality for pediatric cardiac surgery, collectively, has been demonstrated in teaching institutions with large cardiac surgical volumes.11, 22, 23 For HLHS, 15% of stage I palliation may be occurring in nonteaching hospitals.6 This is surprising, given that teaching hospitals are perceived to provide a higher quality of care for the treatment of rare disease and complex patients.24 We undertook the present study to evaluate the mortality of children with HLHS undergoing stage I surgical palliation when performed in teaching and nonteaching hospitals.
| METHODS |
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The study population was identified using the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnostic and procedural codes based on previous studies with HLHS.6, 25, 26 Inclusion criteria for the study population were the ICD-9-CM diagnostic codes for HLHS (746.7), mitral stenosis (746.5), aortic atresia/stenosis (747.22), or aortic hypoplasia (747.10) in addition to the procedural code for systemic to pulmonary arterial shunt (39.0). Discharges with the ICD-9-CM procedural codes for modified stage I palliation (right ventricle to pulmonary artery conduit [35.92]) otherwise known as the Sano modification, cardiac transplantation (37.5), stage II surgical palliation (39.21), or stage III surgical palliation (35.94) were excluded.
The main independent variable of the study was hospital teaching status: teaching or nonteaching. In the KID, teaching designation is obtained from the American Hospital Association (AHA) Annual Survey of Hospitals. Teaching hospitals have an American Medical Association-approved residency program or a membership in the Council of Teaching Hospitals. The KID 2000 also recognizes a full-time intern and resident to bed ratio of 0.25 or higher as a teaching hospital criteria. The KID does not contain the residency program type(s) associated with teaching hospitals. The main dependent variable for this study was in-hospital mortality, which was determined by disposition at hospital discharge.
Variables used for the risk adjustment of condition severity among children with HLHS were the presence of aortic atresia, chromosome anomaly, noncardiac structural anomaly, and prematurity/low birth weight.11, 1618, 21 Condition-severity diagnoses were identified using ICD-9-CM diagnostic codes based on previous studies in patients with congenital heart disease.11
To adjust in-hospital mortality for institutional surgical volume, individual hospitals were categorized into 4 categories based on their annual HLHS stage I palliation volume.23 Individual hospitals were identified using the KID synthetic hospital number.27 Categories were determined from quartiles28 of the median and interquartile range of stage I palliation institutional volume. The median and interquartile range were determined from actual, unweighted discharges within each hospital performing stage I palliation identified in the KID 1997 and 2000 data sets. Stage I palliation volume for each hospital was multiplied by a factor of 1.25 to account for the random 80% hospital discharge sampling of the KID 1997 and 2000.27, 29
Summary statistics were calculated. To determine the percentage of stage I palliation occurring in teaching and nonteaching hospitals, discharges were clustered within each hospital, stratified by hospital-specific stratum, and weighted to derive national estimates of the number of discharges within each hospital type. Continuous variables with a nonnormal distribution (age at admission, institutional volume) were compared with hospital teaching status by median (interquartile range) and Wilcoxon rank sum tests. Categorical variables were compared with a Rao-Scott
2 test to account for clustering, stratification, and weighting. Ordinal variables (institutional volume) were compared with mortality using a
2 trend test. Logistic regression was used for the risk-adjusted multivariate analysis of in-hospital mortality. Univariate predictors of mortality with P
.1 were entered into the final regression model. Statistical Analysis Software (SAS Institute, Inc., Cary, NC) version 9.1.3 was used for all analyses.
| RESULTS |
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The median age of admission at a stage I palliation hospital was 1 day (interquartile range [IQR] 04 days in 1997 and 06 days in 2000). The study population was 63% male for both years combined. Teaching hospitals cared for all patients with a chromosomal anomaly in 1997 and 2000 (Table 1).
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.01) with a similar trend (47% to 19%) (Table 3). In 1997, in-hospital mortality remained higher in nonteaching hospitals (OR: 2.6; 95% CI: 1.35.3) after controlling for stage I palliation hospital volume and the condition-severity diagnoses of prematurity/low birth weight and a noncardiac structural anomaly (Table 4). Mortality was higher in the lowest stage I palliation volume quartile compared with the highest stage I palliation quartile (OR: 3.1; 95% CI: 1.18.3) in the multivariate analysis. The presence of a noncardiac structural anomaly remained a predictor of in-hospital mortality (OR: 3.5; 95% CI: 1.77.2) in the multivariate analysis. Prematurity/low birth weight remained predictive of in-hospital mortality (OR: 2.9; 95% CI: 1.17.4) (Table 4). Multivariate analysis was not performed for the data from 2000, because mortality did not vary by hospital teaching status in the univariate analysis from that year.
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| DISCUSSION |
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No previous studies have compared the in-hospital mortality of stage I palliation for HLHS by hospital teaching status. Nonteaching hospitals have been associated with increased in-hospital mortality for adults undergoing complex surgery.30 However, after adjusting for hospital procedure volume, teaching status was not associated with mortality.30 In our study, the relationship of mortality and hospital teaching status was not affected by stage I hospital volume in 1997.
The volume-outcome relationship demonstrated in this study agrees with previous research on the institutional volume of stage I palliation.26 The finding of mortality approaching 50% for hospitals performing 1 to 2 cases per year is similar to the findings of Checchia et al.26 In our study, the 1997 empiric cut point for the low and mid-low quartiles was between 1 and 2 cases per year. The practical difference in performing 1 vs 2 stage I palliation cases per year may be minimal. However, mortality decreased by 22% across this change in volume in 1997.
No previous study has documented the decrease in utilization of nonteaching hospitals for patients with HLHS undergoing stage I palliation. Our study demonstrates a shift in the number of discharges from nonteaching to teaching hospitals between 1997 and 2000. This change in utilization is reflected in the higher institutional volume of teaching hospitals compared with nonteaching hospitals in 2000. A legislated or mandated effort to centralize stage I palliation into teaching hospitals did not occur between 1997 and 2000. However, the public release of quality report cards for New York City hospitals performing cardiac surgery from the early 1990s generated a renewed interest in health services outcomes.35 Referral patterns in New York for adult cardiac surgery were impacted by this reporting36 with institutional volume shifts away from high-mortality outliers.37 Centralization of pediatric cardiac surgery in Sweden was also occurring during this time.38
Although this study cannot quantify the impact centralization alone had on patient survival, the reduction in mortality observed in patients with HLHS undergoing stage I palliation between 1997 and 2000 is consistent with intrainstitutional improvements in stage I palliation care. A better understanding of postoperative hemodynamics emerged in the late 1990s.41 Institutional-based approaches to the selection and postoperative care for patients undergoing stage I palliation in teaching hospitals resulted in decreased mortality.14, 39 Although classic stage I palliation remained the mainstay for HLHS treatment during this time, a modified version associated with improved operative mortality emerged in the late 1990s.8, 40
Reasons for the increased mortality observed in nonteaching hospitals from 1997 cannot be determined from the present study. Stage I palliation relies heavily on postoperative intensive care. Better risk-adjusted survival rates have been demonstrated in intensive care units associated with teaching hospitals compared with nonteaching hospitals.31 Improved outcomes have been demonstrated in children receiving specialty care and undergoing specialty surgery in dedicated pediatric facilities.3234 Teaching hospitals may have had improved access to pediatric surgical and medical specialists, as well as an ancillary staff, who were better equipped to care for medically complex infants and children in 1997.
It is noteworthy that the nonteaching hospitals that provided stage I palliation in 2000 achieved results as good as those in teaching hospitals. This complicates the arguments for why increased mortality was observed in nonteaching hospitals in 1997. Regardless of the historic findings, our data suggest that these hospitals can perform stage I palliation surgery with equivocal mortality. Despite the improvement in mortality observed in nonteaching hospitals in 2000, however, hospitals performing a low number of operations continued to experience high mortality. The institutional volume-outcome relationship for pediatric cardiac surgery and stage I palliation has been well-established.22, 23, 26 Limited access to higher-volume hospitals and patient preference for local health care may be contributing factors for the continued use of low-volume hospitals in 2000.42
Our study has several limitations. Variation in selection criteria for patients with HLHS undergoing stage I surgical palliation from administrative databases can lead to different results.43 Gutgesell and Massaro25 and Connor et al6 each used different combinations of ICD-9-CM procedural codes to identify patients with HLHS undergoing stage I palliation. Multivariate analyses were performed with the patient selection criteria used in these studies. Our main study findings remained unchanged (results are available on request from the authors).
Patients with HLHS undergoing modified stage I palliation could have been included in the KID 2000 study population. We accounted for this possibility by excluding discharges with the ICD-9-CM procedural code for placement of a right ventricle to pulmonary artery conduit, which is the defining feature of the modified operation.8
Variation in criteria used to identify teaching hospitals could lead to different results. The KID 2000 includes an intern and resident-to-bed (IRB) ratio of 0.25 or greater as a teaching hospital criteria. The KID 1997 does not use this criterion. The American Hospital Association (AHA) uses the IRB ratio of 0.25 to stratify teaching hospitals into major and minor categories.44 The AHA does not use this ratio to determine hospital teaching status (ie, teaching or nonteaching). Therefore, the addition of this ratio into the KID 2000 teaching hospital criteria should not affect the present study findings.
The teaching status of hospitals performing stage I palliation could have changed between 1997 and 2000. Hospitals within the KID 1997 and 2000 data sets cannot be linked together. However, we determined that 3 nonteaching hospitals performing stage I palliation in 1997 were classified as teaching hospitals in 2000 (Pamela Owens, PhD, Agency for Healthcare Research and Quality, personal communication, September 5, 2005).
The residency or fellowship program type(s) associated with an AHA teaching designation is not available within the KID. The KID does not contain health care provider type information (ie, adult or pediatric provider, specialty type, and so on). We therefore could not originate a priori hypotheses regarding the type of residency program or provider type and the effect on mortality for the present study.
A selection bias for low-risk patients to undergo stage I palliation within teaching hospitals could have occurred in 1997. Patients in teaching hospitals who were at risk for increased mortality for stage I palliation could have been selected to undergo cardiac transplantation or comfort care. However, patients with HLHS in teaching hospitals did not experience higher rates of comfort care in 1997.6 The percentage of patients with HLHS undergoing transplantation in teaching and nonteaching hospitals was also similar in 1997.6
Controlling for stage I palliation condition severity is limited by the use of ICD-9-CM codes. Specific cardiac anatomic findings associated with mortality such as a restrictive atrial septum and decreased ascending aortic diameter are not available within ICD-9-CM diagnostic codes. The KID 1997 and 2000 do not contain intraoperative variables such as circulatory arrest time, which have been associated with mortality for stage I palliation.
The interpretation of centralization of stage I palliation into teaching hospitals is limited by the KID sampling design. National estimates of the number of discharges can be obtained using the KID sample design. However, national estimates of the number of hospitals performing stage I palliation cannot be obtained from the KID sampling design. Therefore, we could not accurately determine if the number of nonteaching hospitals performing stage I palliation decreased from 1997 to 2000. The KID is currently available for the years 1997 and 2000 only. Data for the intervening years are unavailable. We were unable to determine if the change in utilization was an ongoing trend or an acute change.
The ability to generalize the main findings is limited by the KID 1997 and 2000 sampling design. The KID 1997 does not include hospital discharges from the states of Michigan and Texas, both of which contain high-volume pediatric cardiac surgical teaching hospitals. The KID 2000 includes discharges from Texas but not Michigan. Texas was included in the KID 2000 analyses to preserve the weighting mechanism used to achieve national estimates of utilization.
Despite these limitations, this study suggests that nonteaching hospitals were associated with higher mortality for patients with HLHS undergoing stage I palliation in 1997. A significant reduction in the number of stage I palliation operations performed in nonteaching hospitals occurred between 1997 and 2000. This centralization of stage I palliation into teaching hospitals, along with advances in postoperative medical and surgical care for these children, was associated with a decrease in mortality. Still, a substantial number of hospitals performing stage I palliation may be operating on a small number of cases and experiencing increased in-hospital mortality. Efforts to decrease mortality within low-volume hospitals or increase access to higher-volume hospitals should be investigated.
| ACKNOWLEDGMENTS |
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We thank Pamela Owens, PhD, from the Agency for Healthcare Quality and Research, for her collaboration on this work.
| FOOTNOTES |
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Address correspondence to Jay G. Berry, MD, Harvard Pediatric Health Services Research Fellowship Program, 1 Autumn St, AU-522, Boston, MA 02115. E-mail: jay.berry{at}childrens.harvard.edu
The authors have indicated they have no financial relationships relevant to this article to disclose.
This study was presented in part at the Pediatric Academic Societies meeting; May 1, 2004; San Francisco, CA.
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