lobectomies and wedge resections of the lung are performed using either open thoracotomy or minimally invasive techniques , particularly , video - assisted thoracoscopic surgery ( vats ) . the literature documents many purported benefits of vats for major lung surgeries , such as smaller incisions , less pain , less blood loss , less respiratory compromise , faster recovery times translating into shortened hospital lengths of stay , and superior survival rates . however , compared to open procedures , vats has higher equipment costs , increased operating room times , and a learning curve for both surgeons and operating room personnel .   during the past three decades , a large body of empirical literature has established a positive relationship between provider volume and patient health outcomes across various medical and surgical procedures [ 310 ] , with little attention paid to thoracic surgery . this is important , as the magnitude of the volume outcome effect was found to vary across health conditions and surgery procedures . the reason that greater volume is associated with better throughput , clinical outcomes , and control over resources , is not well understood . this relationship may be the result of surgeons '  learning - by - doing  and/or the result of  selective referrals , where physicians with better outcomes command a higher demand for their services . to date , most of the work on volume outcome relations was conducted at the hospital level , as opposed to the surgeon level . in the case of lung surgery , patients who received open lobectomy and other resections at high - volume hospitals were less likely to experience postoperative complications and enjoyed better long - term and short - term survival rates [ 1113 ] . a similar relationship between hospital volume and patient outcomes has been observed across patients receiving minimally invasive procedures ; for example , minimally invasive endovascular interventions for patients with abdominal aortic aneurysms [ 1416 ] . recently , there is some evidence that the associations between hospital volume and operative mortality are mediated by surgeon volume [ 14 , 17 ] . the volume of the surgeon was found to have a greater influence on patient outcomes than hospital volume . this should come as no surprise , as hospital volume is the aggregate of all participating surgeons ' volumes . surgeons make preoperative and intraoperative decisions , affect case selection , and determine the appropriate surgical technique to be used . a majority of cancer studies find that high - volume surgeons have a lower rate of operative mortality , with the strength of the relationship varying by condition and procedure [ 14 , 19 ] . conclusions may be obscured by heterogenous definitions of high - volume across studies and procedures . few studies have examined the relationship between surgeon volume and operative mortality for lobectomies and wedge resections [ 18 , 20 , 21 ] . in one such study , high volume surgeons were found to have less locoregional recurrence of cancer , but no differences were observed for mortality . while thoracic surgeons were more likely to perform lobectomies and wedge resections using vats , adjusting for surgeon and hospital volume , lung cancer patients treated by general thoracic surgeons had a lower probability of death than those treated by cardiothoracic surgeons or general surgeons . a number of case studies based on either a single center or a single surgeon found greater experience with vats to improve such patient outcomes as blood loss , recurrence , operation time , surgeon - related thoracotomy conversions , and readmissions [ 2224 ] . understanding volume - outcome relationships is of considerable practical importance because it quantifies the effects of experience on clinical outcomes . even though surgeons often use different techniques ( e.g. , open procedure versus vats ) , studies have not accounted for technique - specific experience in calculating volume . to our knowledge , this is the first study to accumulate experience with vats separately from experience with open procedure , as the two techniques command different surgical skills . information regarding skill development through practice is an important factor that may affect patient decisions of where to seek treatment and provider decisions about where to refer their patients . furthermore , transitioning from open to vats procedures is not trivial , hence it is important to study the degree of transferability of experience across the two procedures . volume - outcome studies of cancer patients have reported mortality , inpatient length - of - stay , readmissions , and several specific clinical indicators , such as blood loss and perioperative complications [ 26 , 27 ] . recent studies documented variations among physicians in their ability to shorten the length - of - stay for their patients , reduce resource utilization , improve quality , and reduce the likelihood of hospital - borne infections . this current work aims to quantify the impact of a surgeon 's volume on outcomes in lung surgery , adjusted for other potential explanatory variables . we studied performance on lobectomies and wedge resections separately and accounted for the experience of surgeons as represented by six - month case volumes using both vats and open techniques . also , we analyzed the effect of this technique - specific experience on inpatient costs , length of surgery , length of stay , as well as the likelihood and number of adverse surgical events . a protocol describing the analysis objectives , criteria for patient selection , data elements of interest , and statistical methods was submitted to the new england institutional review board ( neirb ) , and exemption was obtained.the study was funded by ethicon endo - surgery inc . this study utilizes the premier hospital database , which contains clinical and utilization information on patients receiving care in over 600 usa hospitals and ambulatory surgery centers across the nation . the database contains complete patient billing , hospital cost , and coding histories from more than 25 million inpatient discharges and 175 million hospital outpatient visits . since vats is a new technology , the analyzable dataset was restricted to procedures occurring in 2007 - 2008 . eligible patients were those of any age undergoing vats lobectomy or wedge resection for cancer . international classification of diseases , 9th revision ( icd-9 ) diagnosis codes and procedure codes for identifying lobectomy and wedge resection procedures , cancer diagnoses , comorbid conditions , and all adverse events are listed in tables 710 . for example , many studies defined physician volume as the number of surgeries done over a specific time period and used that measure to predict outcomes of each surgery performed within that same time period [ 8 , 9 , 12 , 14 , 28 ] . as a result , experience not yet acquired was used to describe current performance , which could potentially overestimate the influence of volume on surgeon outcomes .   for each outcome - surgeon combination , volume - accumulated experience over running six - month windows involved recording surgeons ' volume at a given date as the number of procedures accumulated during the prior six months . this measure is more precise than fixed calendar periods and was used extensively in the literature , as it responds instantaneously to any changes in the surgeon 's recent experience profile . experience accumulation with moving , rather than fixed , windows can be viewed as smoothing the calendar step function and alleviating the imprecision that increases for observations occurring toward the end of the observation period . initial counts , percentages , means , and standard deviations for patient demographics , comorbid conditions , hospital characteristics , as well as safety utilization and cost outcomes were summarized separately for vats lobectomy versus vats wedge resection and separately for thoracic surgeons versus all surgeons using descriptive statistics . type of surgeon ( thoracic versus general ) was identified via physician identification codes provided in the database . the safety outcomes of interest were pertinent adverse events occurring during or up to 3060 days after surgery . a dichotomous variable was used indicating the existence of an adverse event as well as a continuous variable tallying the number of adverse events . utilization outcomes were surgery duration ( hours ) and hospital length of stay ( days ) . cost outcomes were total hospital costs per patient , both fixed and variable . since we only studied vats procedures , we did not include costs for initial acquisition of the vats equipment . the key explanatory variable was each surgeon 's volume for lobectomy and wedge resection using vats or open thoracotomy techniques . this measure of volume corresponded to the aggregate experience level of the surgeon over running six - month windows . experience with open thoracotomy procedures may or may not contribute to performance with vats , but it is certainly expected that experience specific to vats will be the most relevant in explaining outcomes for patients treated with vats . multivariable logistic regression analyses were estimated for the adverse event binary outcome : the presence or absence of specific individual events . ordinary least squares ( ols ) regression was used for all other continuous outcomes such as hospital costs , surgery time , length of stay , and number of adverse events . for all models , in addition to the volume measures , the following explanatory variables were included : age , gender , race , marital status , insurance type , diagnosis ( metastasis versus primary cancer ) , comorbid conditions ( e.g. , diabetes ) , all patient refined - diagnosis - related groups ( apr - drgs ) severity index ( an index of comorbidity unique to the premier database that reflects preoperative severity level ) , census region of hospital , rural versus urban hospitals , teaching versus nonteaching hospitals , and number of hospital beds .   using these explanatory variables , multivariable models were estimated to isolate the effects of a surgeon 's vats volume on adverse events , hospital costs , surgery time , and length of stay . because the cost and utilization variables were right skewed , they were converted to natural logarithms to normalize their distributions , although the results were not sensitive to this transformation . weights provided in the premier database were used to transform the results in a manner that permitted generalizability to the usa population . all analyses were performed using stata version 10 ( statacorp lp , college station , texas , usa ) . of 7,137 patients in the database with elective , inpatient resections for lung cancer , a total of 2,698 patients underwent lobectomy ( n = 716 ) or wedge resection ( n = 1982 ) using vats . more than 70% of these procedures were performed by thoracic surgeons ( n = 1,896 ) . there were slightly more females than males in all four samples , and most patients in all samples were over 60 years of age and covered by medicare . most patients were caucasian , with primary ( as opposed to metastatic ) neoplasm of the lung and only minimal to moderate illness severity level , as measured by the apr - drg severity index . as expected , the severity index for patients undergoing lobectomy was higher than for patients undergoing wedge resection . patient characteristics within procedure ( lobectomy versus wedge resection ) were similar across the thoracic surgeons sample and the all surgeons sample . the most frequent comorbidities reported were chronic obstructive pulmonary disease ( copd ) , diabetes mellitus , and heart disease . patient - weighted hospital characteristics for the four samples are reported in table 3 . compared with patients undergoing vats wedge resection , patients undergoing vats lobectomy were more likely to receive the procedure in a teaching hospital ( 63% versus 57% ) and in a hospital with over 600 beds ( 46% versus 38% ) . all samples exhibit similar demographic distributions . average hospital costs , surgery time , length of hospital stay , the likelihood , and number of adverse events , as well as the surgeons ' volume measures for each sample were examined prior to multivariable modeling . the data suggest that , on average , vats lobectomies cost hospitals more than vats wedge resections ( $ 19,697 versus $ 13,058 ) are associated with both longer surgery time ( four hours versus 2.5 hours ) and longer lengths of hospital stay ( 5.7 days versus 3.9 days ) . furthermore , patients undergoing lobectomy had a higher likelihood of experiencing an adverse event compared to patients undergoing wedge resection ( 0.57 versus 0.43 ) and had a higher number of adverse events on average ( 1.13 events versus 0.72 events ) . this study tracks 575 surgeons performing lobectomies or wedge resections using vats ( 366 of whom were thoracic surgeons ) . patients treated by thoracic surgeons using vats lobectomy had lower inpatient costs and shorter length of stay compared with patients seen by general and other surgeons . while these effects were statistically significant at the 1% level , they were evidently small . no other statistically meaningful differences between thoracic and other surgeons were found for patients treated using vats wedge resection or for other outcomes ( i.e. , length of surgery , likelihood of adverse event , and number of adverse events ) . the most experienced surgeons , on average , are found in the sample of thoracic surgeons performing vats lobectomies , 31.6 procedures . six months experience , for these surgeons , with open lobectomies and open wedge resection was lower , 5.4 procedures and 3.9 procedures , respectively , for the entire sample . given the possibility of confounders in these group comparisons of outcomes , we performed multivariable regression analyses , adjusting for a number of potential confounders , including patient demographics , metastatic versus primary cancer , comorbid conditions , apr - drg severity index , and hospital characteristics . the results of these adjusted analyses of costs , surgery time , length of stay , likelihood of adverse event , and the number of adverse events are shown in table 5 . for ease of interpretation , we report the estimated marginal effects for each one of the 40 models presented in table 5 . the reported marginal effects measure the expected instantaneous change in each one of our five - outcome variables as a function of a change in surgeons ' vats volume , while keeping all the other covariates constant . note that , for each outcome of interest , we compared the estimated marginal effects obtained from an unadjusted analysis with the estimated marginal effects from the multivariable analysis described above . ( note : only adjusted findings are reported in table 5 ) . in the unadjusted analysis for the all surgeons lobectomy sample , doubling the average surgeon 's volume was associated with a 10% reduction in inpatient cost ( $ 2,029 ) , a 5% reduction in surgery time ( 13 minutes ) , and a 15% reduction in length - of - stay ( approximately one day ) . the effect of experience on the likelihood of an adverse event , while statistically significant , was small in magnitude . increased surgeons ' experience was associated with a reduction of one adverse event in one of every five patients . even after adjusting for the variables detailed in tables 1through 3 , all the findings above persist . the first and second columns of table 5 reports the analysis for lobectomies for all surgeons and then surgeries performed exclusively by thoracic surgeons . for the most part , doubling of the thoracic surgeons experience was associated with a 13% reduction in inpatient cost ( $ 2,409 ) and a 7% reduction in surgery time ( 18 minutes ) . the second and third columns of table 5 repeat the analysis for patients undergoing vats wedge resection . here , for most outcomes and specifications , the volume - outcome relationship appears much weaker . doubling of the surgeon 's experience was associated with a 3% reduction in inpatient cost ( $ 389 ) , a 2% reduction in surgery time ( 3 minutes ) , and an 8% reduction in hospital length of stay ( a third of a day ) . the results were similar when considering the most saturated model and when limiting the sample to procedures performed solely by thoracic surgeons . the only exception was the reduction in cost for the thoracic surgeon sample , which was 5% ( $ 659 ) . table 6 reports results from models similar to those reported in table 5 , and includes two additional variables : the surgeon 's six - months experience with open lobectomies and the surgeon 's six - months experience with open wedge resections . the two additional volume measures allow for assessing the contribution of competing sources of learning . for example , for the vats lobectomy sample , one may argue that any experience with lobectomy ( open or vats ) may be an important contributor for performance . overall we find the volume - outcome relationship for experience with vats to be similar in sign , magnitude , and statistical significance to those described in table 5 . experience with open lobectomy did not have an effect on outcomes for patients treated with vats lobectomy , with the exception of the number of adverse events , where greater experience with open lobectomy was associated with a small reduction in the number of adverse events for vats lobectomy . similarly , experience with open wedge resection was associated with a reduction in inpatient cost and length of stay beyond the reductions associated with greater experience with vats . an important strength of the premier database is that it provides very large numbers of patients , surgeons , and procedures on a nationwide scale . obtaining this extremely large sample size from a practical setting allows researchers to better understand processes such as the relationship between surgeons ' volume and outcomes . in turn , this analysis provides hospitals , patients , and surgeons with a quantifiable measure of the benefits of surgeons ' volume on outcomes in lung surgery . the sample size and large number of elements in the premier database allows for analyzing the effect of experience with vats on inpatient costs , length of surgery , length of stay , as well as the likelihood and number of adverse surgical events . in this retrospective analysis the relationship is stronger ( 1 ) for cost and utilization outcomes as opposed to adverse events , ( 2 ) for thoracic surgeons rather than other surgeons , and ( 3 ) for vats lobectomy procedures more than for vats wedge resection procedures . finally , we find that while there was a reduction in cost and resource utilization associated with greater experience with vats , these outcomes were not strongly linked with greater experience with open procedures . thus , by and large , performance with vats is associated primarily with experience with vats . the choice between vats and open lobectomy has implications for the surgeon 's learning profile , as the reduction in cost and resource utilization associated with greater experience with vats were much larger than those associated with greater experience with open procedures . this finding reinforces the need for surgeons ' specialization and centralization of delivery for vats . this is a retrospective analysis from a transactional database ( premier ) and not a prospective analysis where randomization and more detailed information about patients and procedures could be collected . for instance , it would have been of interest to examine the influence of additional patient characteristics , such as weight or bmi , and more procedure - related details . nevertheless , we include numerous controls in our analysis , particularly , controls for patient characteristics   and hospital characteristics . another limitation , and a topic that can be the focus of future research , is the lack of information on surgeons ' characteristics . in particular , data associated with surgeons ' characteristics ( e.g. , years in practice , graduate of which medical school , completion of fellowship , etc . ) this information may be important as surgeons do not randomly adopt vats , and the results may therefore be biased if the most able surgeons are also the ones who adopt and utilize vats extensively . our analysis of a large , nationally representative hospital database revealed three key findings : ( 1 ) there is a reduction in cost and resource utilization associated with greater experience with vats , especially for vats lobectomy for lung cancer ; ( 2 ) thoracic surgeons have better vats outcomes than non - thoracic surgeons ; ( 3 ) greater experience with open procedures does not correlate with better vats outcomes . these findings have implications for the organization of health care delivery of both minimally invasive and open procedures .
this study examined the effect of surgeons ' volume on outcomes in lung surgery : lobectomies and wedge resections . 
 additionally , the effect of video - assisted thoracoscopic surgery ( vats ) on cost , utilization , and adverse events was analyzed . 
 the premier hospital database was the data source for this analysis . 
 eligible patients were those of any age undergoing lobectomy or wedge resection using vats for cancer treatment . 
 volume was represented by the aggregate experience level of the surgeon in a six - month window before each surgery . 
 a positive volume - outcome relationship was found with some notable features . the relationship is stronger for cost and utilization outcomes than for adverse events ; 
 for thoracic surgeons as opposed to other surgeons ; for vats lobectomies rather than vats wedge resections . while there was a reduction in cost and resource utilization with greater experience in vats , these outcomes were not associated with greater experience in open procedures .