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A study of 11,003 patients with hypertrophic pyloric stenosis and the association between surgeon and hospital volume and outcomes

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A study of 11,003 patients with hypertrophic pyloric stenosis and the association between surgeon and hospital volume and outcomes
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  A study of 11,003 patients with hypertrophic pyloricstenosis and the association between surgeon andhospital volume and outcomes Shawn D. Safford a, *, Ricardo Pietrobon b , Kristine M. Safford a ,Henrique Martins b , Michael A. Skinner  a , Henry E. Rice a a   Division of Pediatric Surgery, Department of Surgery, Duke University Medical Center, Box 31291, Durham, NC 27710, USA  b Center for Excellence in Surgical Outcomes, Duke University Medical Center, Durham, NC 27710, USA AbstractAim:  The availability of large clinical databases allows for careful evaluation of surgical practices,indicators of quality improvement, and cost. We used a large clinical database to compare the effect of surgeon and hospital volume for the care of children with hypertrophic pyloric stenosis (HPS). Methods:  Patients with International Classification of Diseases-9 codes for HPS and pyloromyotomywereselectedfromthe1994to2000NationalInpatientSamplesdatabase.Multipleandlogisticregressionmodels were used to evaluate the risk-adjusted association between provider volume and outcomes. Results:  Postoperative complications occurred in 2.71% of patients. Patients operated on by low- andintermediate-volume surgeons were more likely to have complications compared with those operated on by high-volume surgeons (95% confidence interval [CI], 1.25-3.78 and 95% CI, 1.25-2.69, respectively).Patients operated at low-volume hospitals were 1.6 times more likely to have complications comparedwith those operated atintermediate- or high-volume hospitals (95% CI, 1.19-2.20). Procedures performedat high-volume hospitals were less expensive than those at intermediate-volume hospitals by a margin of $910 (95% CI, $443-$1377). Conclusions:  These data represent the largest study to date on the epidemiology, complication rate, andcost for care for HPS. Patients treated by both high-volume surgeons and at high-volume hospitals haveimproved outcomes at less cost. D  2005 Elsevier Inc. All rights reserved. Hospital and surgeon volume are associated withimproved outcomes for various operations [1,2]. Since the first volume-outcome study by Luft et al [3] more than2 decades ago, most studies have focused on adult high-risk surgical conditions. Recent investigations in children havesuggested similar  associations between volume and out-come in children [4-6]. Whereas most complex pediatricssurgical operations are performed by pediatric surgicalspecialists, hypertrophic pyloric stenosis (HPS), the most common surgical disease in infants, is frequent ly treated by both general- and specialty-trained surgeons [7]. Previousstudies with both HPS as well as other common pediatric 0022-3468/$ – see front matter   D  2005 Elsevier Inc. All rights reserved.doi:10.1016/j.jpedsurg.2005.03.011Presented at the 56th Annual Meeting of the Section on Surgery of the American Academy of Pediatrics, San Francisco, California, October 8-10, 2004. T  Corresponding author. Tel.: +1 919 681 5077; fax: +1 919 681 8353.  E-mail address:  saffo001@mc.duke.edu (S.D. Safford). Index words: Hypertrophic pyloricstenosis;Pyloromyotomy;Mucosal perforation Journal of Pediatric Surgery (2005)  40 , 967–973www.elsevier.com/locate/jpedsurg  surgical diseases have yielded conflicting results regardingthe effect of pediatric surgery subspecialty training on thesurgical outcomes [8-10].The availability of large clinical databases allows for careful evaluation of surgical practices, indicators of qualityimprovement, and cost analysis. For HPS, the effect of subspecialty training as well as other variables on improvedoutcomes is unclear. We hypothesized that high-volumesurgeons and hospitals would have improved outcomescompared with intermediate- and low-volume surgeons andhospital. We used a large clinical database to analyzecomplications, length of stay (LOS), and costs for care of children with HPS. In addition, we reviewed the current epidemiology of HPS. 1. Methods 1.1. Study population and description of databases Patients with International Classification of Diseases(ICD)-9 diagnosis and procedure codes for congenital HPS(750.5) and pyloromyotomy (43.3) or pyloroplasty (44.2)were selected from the 1994 to 2000 National Inpatient Samples (NIS) (National Technical Information Service,Springfield, Va). Using these databases, a total of 11,003 patients were identified containing these diagnostic and procedure codes. For these patients, hospital identifiers were present for all patient records and surgeon identifiers wereavailable on 5698 patient records.The NIS databases are among the largest publiclyavailable inpatient databases in the United States and are part of the Healthcare Cost and Utilization Project  spon-sored by the Agency for Research and Quality [11]. The1994 to 2000 NIS databases contain information onapproximately 5 to 8 million discharges from a sample of more than 1000 hospitals in 28 states. The NIS dataapproximate a 20% stratified probability sample re presen-tative of community hospitals in the United States [11].The Healthcare Cost and Utilization Project hasassigned validation and quality assessment of these datasets to an independent contractor  [11]. The validation was performed by reviewing univariate statistics for all numericdata elements, frequency distributions for all categoricaland some continuous data elements, checking rangesagainst standard norms, and performing edit checks toidentify inconsistencies between related data elements.Furthermore, the NIS data compare favorably with the National Hospital Discharge Survey for many diseaseestimates [12,13].This study was approved from the Institutional ReviewBoard at Duke University Medical Center. 1.2. Outcome measures To assess clinical outcomes, we measured LOS, rate of complications, mortality, and inflation-adjusted costs.Length of hospital stay (days) was defined as the difference between date of admission and date of discharge. Length of stay was coded as zero for patients who were dischargedduring the same day of admission. Complications weregrouped into 8 categories including mechanical wound,infections, urinary, pulmonary, gastrointestinal, cardiovas-cular, systemic, and complications occurring during the procedure (Table 1).We stratified outcomes based on age of patient, surgeonvolume, and hospital volume. We evaluated volume as acontinuous (log-transformed) variable and created categor-ical variables for age, hospital volume, and surgeonvolume. We selected cutoff points that sorted patients int o 3evenly sized groups with low, medium, and high volume [2].Based on these categories, we defined surgeon volume aslow ( b 1 case per year), medium (1-5 cases per year), andhigh ( N 5 cases per year) and hospital volume as low( b 5 cases per year), medium (5-15 cases per year), and high( N 15 cases per year). 1.3. Statistics All statistical analyses were performed using Stataversion 8.0 (Stata Corporation, College Station, Tex).Differences between patients who underwent procedures by different categories of surgeon or hospital volume withrespect to sociodemographic, comorbidity, and other pre-dictor variables were tested using the Student’s  t   tests, v 2 tests, and analysis of variance.Multiple linear regression models were used to examinethe risk-adjusted association between surgeon or hospital Table 1  Descriptive statistics of age, race, sex, complicationtypes, and volume of surgeons and hospitalsVariables Frequency PercentageAge (n = 9716) 0-27 d 2882 29.727-39 d 3667 37.7 N 39 d 3167 32.6Race (n = 8445) White 5969 70.7Afro-American 714 8.50Other 1762 20.9Sex (n = 11,003) Male 9135 83.0Female 1868 17.0Complications(n = 299)Mechanicalwound17 6.16Infection 28 10.14Urinary 3 1.09Pulmonary 63 22.83Gastrointestinal 47 17.03Cardiovascular 19 6.88Systemic 1 0.36Complicationsduring procedure121 43.84Surgeon rangeof volume31.8  F  40.5Hospital rangeof volume92.3  F  100 S.D. Safford et al.968  volume and log-transformed LOS and inflation-adjustedcharges. Length of stay and inflation-adjusted charges presented a right-skewed distribution and were modeled intheir log-transformed form. Estimated predictions wereexponentiated. To assess the risk-adjusted impact of  provider volume on other dichotomous variables, we usedlogistic regression analyses. All models were adjusted for  patients’ comorbidity, age, sex, race, income, and geographiclocation. For calculation of the incidence of surgical cases of  pyloric stenosis, we used the total number of cases reportedin the NIS database stratified by month and year. 2. Results 2.1. Epidemiology of HPS We found that the incidence of HPS in the United Statesranged from 8.2 to 12.3 cases per 1000 live births between1994 and 2000. The mean age of children with HPS was41.1 days (range, 1 day-3 years) and most of t hese childrenwere male (83%) and white (70.7%) (Table 1). To evaluateif the incidence of pyloric stenosis was associated withseasonal variations, we compared the incidence of HPS per hospital admission over calendar year. The rates of admission for HPS were constant throughout the year andranged from 1.1 to 1.2 per 1000 hospital admissions everymonth. Similarly, when stratified based on seasons, wefound no differences in incidence of HPS admissions(winter, 1.1 per 1000; spring, 1.2 per 1000; summer,1.2 per 1000; and fall, 1.3 per 1000;  P   = .46). 2.2. Descriptive statistics of pyloromyotomy Hospital volume ranged from 1 to 323 cases over the7 years of our study. This corresponded to the averagehospital performing 92.3  F  100 pyloromyotomies or 13.2 pyloromyotomies per year. For surgeons, case volumeranged from 1 to 173 operations over 7 years correspondingto an average 31.8 F 40.5 case load during the time of studyor an average of 4.6 operations per year. Inflation-adjustedcharges for pyloromyotomy trended to increase over time(US $7246 in 1994 vs US $8102 in 2000,  P   = .06).Complications were relatively infrequent, occurring in2.71% of operations (Table 1). The majority (47.8%) of complications occurred during the procedure, includingmucosal perforation that occurred at a rate of 1.1%.Postoperative complications included pulmonary (22.8%),gastrointestinal (17%), and infections (10.1%). Particularlyremarkable were the cardiac arrests (n = 19); this number corresponded to a 0.01% rate of cardiac arrest in childrenundergoing pyloromyotomy (Table 2). 2.3. Outcomes of pyloromyotomy stratified by ageand volume of surgeon and hospital 2.3.1. Complications High-volume surgeons and hospitals had lower rates of complications when compared with low-volume centers(Table 3). These differences in complication rates translatedto a 1.63 (95% confidence interval [CI], 1.19-2.20) and 2.17(95% CI, 1.25-3.78) increased risk of complications for  patients operated at low-volume centers and by low-volumesurgeons compared with high-volume centers and high-volume surgeons, respectively. High volume surgeons were1.64 (95% CI, 1.25-2.69) times less likely to have compli-cations than medium-volume surgeons.Similarly, high-volume hospitals trended toward fewer complications than medium-volume hospitals (2.27% vs3.33%), but this did not reach a statistically significant value.Extremes of age did not lead to an increased rate of complications. Although there was a trend toward increasedcomplications in the very young ( b 29 days, 3.2% vs N 39 days, 2.1%), this did not reach statistical significance. Table 2  Details of types of complications within each categoryComplications Frequency PercentageComplicationsduring procedureAccidental puncture or laceration complicating surgery 112 1.02Hemorrhage 9 0.09Foreign body accidentally left during procedure 0 0Gastrointestinal Postoperative ileus, obstruction, nausea, vomiting, pancreatitis 47 0.43Peritoneal adhesions with obstruction 1 0.01Colostomy and enterostomy complications 0 0Persistent postoperative fistula 0 0Pulmonary Postoperative atelectasis, pneumonia 50 0.45Postoperative acute respiratory insufficiency 10 0.09Postoperative acute pneumothorax 3 0.03Postoperative pulmonary edema 1 0.01Cardiovascular Myocardial infraction, cardiac arrest/insufficiency during or resulting from a procedure19 0.17Postoperative pulmonary embolism 0 0Postoperative stroke 0 0Postoperative deep venous thrombosis 0 0 Volume-outcomes relationship for pyloric stenosis surgery 969  During the study, there was only 1 death reported. Thisoccurred at a low-volume center, and the volume category of the surgeon was unknown.We used the complication of cardiac arrest as a marker of the role of anesthetic risk. We stratified cardiac arrest complications for age of patients and volume of surgeon andhospitals. Cardiac arrest occurred in 19 children with noidentifiable predictors of age, hospital volume, or surgeonvolume. The average age of children who arrested was42.8 F 36 days (range, 4-141 days). Five arrests occurred inlow-volume hospitals, 9 in medium-volume hospitals, and 5in high-volume hospitals (  P   = .35). 2.3.2. Mucosal perforation Reduced mucosal perforation rates have been consideredan indicator of  im proved care for children undergoing pyloromyotomy [9]. We specifically analyzed this compli-cation to examine whether the rate of mucosal perforationwas related to surgeon or hospital volume. Low-volumesurgeons and hospitals were responsible for 72% and 64%of all mucosal perforations, respectively (Table 4). Thesedata translated to patients treated by low-volume surgeonsor at low-volume hospitals being 4.0 and 6.7 times morelikely to sustain a mucosal perforation t han by high-volumesurgeons and at high-volume centers (Table 4). Similarly,surgeons at medium-volume hospitals were 2.78 times morelikely to cause a mucosal perforation compared with high-volume hospitals. The perforation rates for medium-volumesurgeons trended toward increased rate of mucosal perfora-tion compared with high-volume surgeons, although thisdifference was not statistically significant. We did not identify a significant difference in rate of mucosal perfora-tion between age groups. 2.3.3. Length of hospital stay Another predictor of clinical outcome that has beenassociated with quality of care is length of hospital stay.These data usually are associated with the level of ancillarysupport, complicat ions associated with procedures, andhospital costs [14]. For pyloric stenosis, patients treated byhigh-volume hospitals and surgeons spent less number of days in the hospital compared with the low-volume hospitals(2.40 vs 2.77 days,  P   b .01) and surgeons (2.50 vs 2.87 days,  P   b .01). This decreased LOS was also seen when comparinghigh- and medium-volume hospit als, but not high- andmedium-volume surgeons (Table 3). 2.3.4. Hospital costs High-volume hospitals were less expensive than medium-volume hospitals by $910 (95% CI, $443-$1377), but not statistically different than low-volume centers. In contrast,high-volume surgeons were more expensive by $511 (95%CI, $25-$997) compared with low-volume surgeons, but not statistically different than medium-volume surgeons. 3. Discussion These data represent the largest study to date on thecurrent epidemiology, complication rate, and cost of care for HPS in the United States. To demonstrate the effect of surgeon and hospital volume on outcome of children treatedfor HPS, we evaluated complication rates, LOS, and hospitalcharges. Overall, high-volume surgeons and hospitals hadimproved outcomes compared with both low- and medium-volume surgeons and hospitals. Interestingly, the care byhigh-volume surgeons and hospitals was at greater cost  Table 3  Stratified outcomes of complication rate, deaths, LOS, and costs based on surgeon volume and hospital volumeComplications Death rate LOS (d) Cost ($)Surgeon volume Low 65 (3.17) 0 (0) 2.87  F 1.63 5815.53  F  1.62Medium 39 (2.18) 0 (0) 2.54  F 1.66 6518.77  F  1.66High 21 (1.13) 0 (0) 2.50  F 1.66 6370.04  F  1.55Hospital volume Low 135 (3.33) 1 (0.02) 2.77  F 1.63 6187.44  F  1.70Medium 80 (2.27) 0 (0) 2.69  F 1.62 6802.97  F  1.69High 61 (1.78) 0 (0) 2.40  F 1.64 6226.41  F 1.55 Data are presented as n (%) unless otherwise indicated. Table 4  Odds risk ratio of mucosal perforation stratified based on surgeon and hospital volumeComplications during the procedure: accidental puncture or laceration complicating surgeryFrequency Percentage Odds ratio  P  Surgeon volume Low 36 1.76 4.01 (1.52-10.56) .005Medium 9 0.50 1.29 (0.41-4.09) .662High 5 0.27 1Hospital volume Low 72 1.77 6.74 (2.68-16.98)  b .001Medium 29 0.82 2.78 (1.03-7.46) .042High 11 0.32 1 S.D. Safford et al.970  compared with low-volume centers, although at less cost compared with medium-volume centers.Hypertrophic pyloric stenosis is the most commoncondition requiring surgery in infants [7]. In this study, wehave found an incidence of HPS of 8.3 to 12 cases per 1000 live births in the United States, an incidence higher than noted in previous reports of 2 to 5 per 1000 live births[7,15]. Similar to previous reports, we found that white males represent most children with HPS [7,15]. In contrast to previous studies suggesting variations of incidence accord-ing to season, we did not identify seasonal variations [16,17].Although we found that the incidence of HPS is markedlyhigher than previously reported, the incidence of cases of  pyloromyotomy per hospital admission remained nearlystable across the 7 years of the study (1.1-1.2 cases per 1000hospital admissions), unlike recent reports of increasingincidence of HPS reported in the United Kingdom [17].Given the large number of children with HPS, the impact of quality improvement has broad clinical consequences.Since the srcinal description of the surgical treatment of HPS from the early 1900s, ongoing controversy hascentered around who should be treating this disease, thegeneral surgeon or the pediatric surgeon [9,10,18]? Previousreports have yielded conflicting results, with 1 report finding equivalent results between general and pediatricsurgeons and other reports suggesting an increased rate of mucosal perforation and wound infection rates by generalsurgeons compared with pediatric surgeons [8]. In a study of a single pediatric surgeon compared with his generalsurgeon colleagues at a single hospital, wound infectionrates were reported to be 15.5% vs 2.8%, wound dehiscence6.7% vs 0%, and duodenal perforation 12.8% vs 0% for  thegeneral surgeon and pediatric surgeon, respectively [19]. Anadditional study of patients with HPS in North Carolinafound no difference for hospital charges ($5110 F $268 vs$5144  F  $252) or LOS (3.1  F  0.2 vs 3.1  F  0.1 days) between general and pediatric surgeons, but did identify alower incidence of mucosal perforation for children t reated by pediatric surgeons (0.55% vs 2.9%,  P   b  .001) [9].Although the bulk of literature on the care of HPSsuggests improved outcomes for children cared for by pediatric surgeons compared with general surgeons, the roleof surgeon and hos pital volume on clinical outcomes remainsunclear  [9,10,18]. Since the first volume-outcome studyreported more than 20 years ago, many studies of variousmedical and surgical conditions have correlated improvedoutcomes when patient s are treated by higher-volume physicians and hospitals [2,3]. However, few of these largeoutcome studies have focused on the importance of volumeon outcome in children [20].For select diseases of childhood, several small series have begun to suggest a similar association bet ween improvedoutcomes and high clinical volume [4-6]. For example,children treated for suspected appendicitis at low-volumecenters were misdiagnosed 50% more frequently than high-volume centers [4]. For the treatment of intussusception, children had decreased risk of requiring surgery, shorter LOS, and lower hospital charges at high-volume hospitalscompared with low-volume hospitals [6]. Our data suggest that for HPS, similar to these other childhood conditions,children cared for by both high-volume surgeons andhigh-volume hospitals result in improved clinical outcomes.For both complications and LOS, we found that high-volume surgeons performed better than both the medium-and low-volume surgeons. For pyloromyotomy, the overallcomplication rate was 2.71%, and this complication rate wasinversely proportional to the volume of surgeon. Childrentreated by high-volume surgeons experienced a complica-tion rate of 1.13% vs 3.17% for low-volume surgeons.Whereas we found an association between complication rateand outcomes, we do note that these complication rates areless than other complication rates reported in the literaturecomparing general and pediatric surgeons [9,19].For LOS, we found that high-volume surgeonsdischarged patients at an earlier time. However, because the LOS wasonly 0.37 days less than low-volume surgeons and hospitals,the clinical significance of this difference is unclear. Some of the difference may be attributed to the transfer of patients tohigh-volume centers from low-volume centers.Mucosal perforation rates have been considered anindicator of standard of care for HPS. Previous reports froma single institution or single region have variable rates of mucosal perforation, although the perforation rates arethought to be higher for general surgeons (4.2%-12.8%)compared with pediatric surgeons (0%-4.3%) [8,9,19]. In our large national study, we have identified an average mucosal perforation rate of 1.02%. High-volume surgeons had a rateof mucosal perforation of 0.27% vs 1.76% in low-volumesurgeons. These data lead to an odds risk ratio of 4.01,suggesting that at least for limiting the risk of mucosal perforation, there is a clear advantage to procedures per-formed by high-volume surgeons.Cardiac arrest, a rarely reported complication of HPS,was identified in 0.17% of children. We did not identify anyeffect of hospital or surgeon volume on the risk of thiscomplication. Although the risk of cardiac arrest is rarelydiscussed in reports of HPS, our rate of cardiac arrest isconsistent with other studies evaluating the risk of var ioussurgicalproceduresundergeneral anesthesia in children [21].In contrast to other studies that found that cardiac arrestsoccurred only children treated by anesthesiologists who didnot care for children regularly, we found that the incidence of cardiac arrest was equivalent among the high-, medium-, andlow-volume centers [22]. Moreover, our data do not suggest that anesthetic risk contributed to variations in surgeon or hospital volume outcome.Hospital charges are frequently used as a benchmark of quality of care and outcome, although debate has centered onthe benefits of increased costs associated with specialty care[6,9]. We found that the inflation-adjusted charges for thecare of HPS ranged from $7198 in 1995 to $8102 in 2002;the increase in costs over the time course of the study trended Volume-outcomes relationship for pyloric stenosis surgery 971
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