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High Volume and Outcome After Liver Resection: Surgeon or Center?

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Journal of Gastrointestinal Surgery Aims and scope

Abstract

Introduction

In a case controlled analysis, we attempted to determine if the volume–survival benefit persists in liver resection (LR) after eliminating differences in background characteristics.

Methods

Using the Nationwide Inpatient Sample (NIS), we identified all LR (n = 2,949) with available surgeon/hospital identifiers performed from 1998–2005. Propensity scoring adjusted for background characteristics. Volume cut-points were selected to create equal groups. A logistic regression for mortality was then performed with these matched groups.

Results

At high volume (HV) hospitals, patients (n = 1423) were more often older, white, private insurance holders, elective admissions, carriers of a malignant diagnosis, and high income residents (p < 0.05). Propensity matching eliminated differences in background characteristics. Adjusted in-hospital mortality was significantly lower in the HV group (2.6% vs. 4.8%, p = 0.02). Logistic regression found that private insurance and elective admission type decreased mortality; preoperative comorbidity increased mortality. Only LR performed by HV surgeons at HV centers was independently associated with improved in-hospital mortality (HR, 0.43; 95% CI, 0.22–0.83).

Conclusions

A socioeconomic bias may exist at HV centers. When these factors are accounted for and adjusted, center volume does not appear to influence in-hospital mortality unless LR is performed by HV surgeons at HV centers.

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Acknowledgement

This study was supported by the American Society of Transplant Surgeons Faculty Development Award, Worcester Foundation for Biomedical Research (SAS) and Howard Hughes Early Career Grant (JFT).

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Correspondence to Shimul A. Shah.

Additional information

Elijah Dixon, M.D. (Calgary, Alberta, CA): Dr. Shah, I would like to congratulate you on a nice presentation and a well written manuscript. You have taken a closer look at the volume outcome relationship as it applies to hepatic surgery and tried to drill down and see what effect the individual surgeon and hospital or institutional volume has on outcomes. The analysis that you used is a combination of standard logistic regression analysis and a case control matched analysis with propensity scores. You found that there were differences in the socioeconomic means of the patients that are treated at high and low volume hospitals, and that the individual effects of both surgeon and hospital volume on outcome are fairly weak, and that only the two of them together show us a statistically significant effect on postoperative mortality. So, I have three quick questions for you.

The first is, can you comment on how significantly you think your results or the lack of volume outcome effect can be explained by differences in case complexity at high and low volume centers and our inability to measure the differences in case complexity using administrative data? The second question. There is some evidence that volume may in fact be a surrogate for other aspects of care, and I wonder if you could hypothesize what some of the structural and process of care issues may be that can explain some of the volume outcome effect. And third, your analysis used two techniques. The case control matched analysis used a much smaller data set, a subset of your data, and I wonder if you could comment on what the value of that analysis is and its relative strength in comparison to the standard multivariate regression.

Thank you. I enjoyed your presentation.

Shimul A. Shah, M.D. (Worcester, MA): To answer your first question, the case complexity is something that we are not going to be able to account for in most administrative databases. Some of the cancer databases might allow us to look at tumor size, but even then, it is not going to give us the accurate assessment of how much work a high volume or low volume surgeon would have to do in a liver resection. And probably in that regard, as some centers have done already, we are going to need to collate some of our data and look at it prospectively and combine centers’ experiences and try to understand this phenomenon. Maybe the high volume surgeons are doing more complex cases, so therefore the mortality benefit that you get is underscored in a study like this.

In terms of processes of care, I think with liver resection it is especially unique and isn't really accounted for in large population-based studies. For instance, high volume centers probably have a multidisciplinary tumor conference; if you work at a transplant center, that might account for improved outcomes after liver resection; whether you are at teaching hospital or a nonteaching hospital; or even something like having two high volume surgeons in a single center that work together during a liver resection probably improves outcomes. These kinds of factors are not accounted for in a large database. Our group has previously shown that liver resection at a transplant center significantly improves outcomes in terms of in-hospital mortality.

The use of propensity scores allows us to do a case controlled analysis. When you perform a logistic regression of thousands of patients, you are assuming that the cohorts are similar when they are not. So although you might find significant factors that are “independent”, we really don't believe that they are truly independent unless you trim down the cohorts and make sure that the demographic and the hospital factors are similar.

Myrddin Rees, M.D. (Baskingstoke, UK): I have been a low volume surgeon in a low volume hospital, and I am currently a high volume surgeon in a high volume hospital, doing over 200 resections of the liver a year. I am also president of your sister organization, the Association of Upper Gastrointestinal Surgeons for Great Britain and Ireland. I would like to give you a U.K. perspective, which I think is relevant to this paper, which I enjoyed very much.

Over the past five years, two important things have occurred in England. We have centralized all major cancer resections for the esophagus, pancreas, and the liver. So we now only have high volume centers. However, we still had a spate of young surgeons being suspended in their first year as a consultant. As a result, AUGIS decreed and advised that all young surgeons be mentored for up to five years. So at my center we have three surgeons, and though I do the majority, my youngest surgeon always has me as first assistant on any difficult operation. As a consequence our results are the same and equal, and I recommend to you the team approach.

Thank you.

Nicholas J. Zyromski, M.D. (Indianapolis, IN): Congratulations on a beautiful presentation of a provocative paper. I understand that your outcome measure on this was specifically in-hospital mortality. My question is, does this database allow you to look at long-term survival and is that something that you are thinking about looking at in this situation?

Shimul A. Shah, M.D. (Worcester, MA): Unfortunately, this database doesn't allow us to look at long-term survival. So one thing that we are going to look into next is some of the cancer databases. Unfortunately, they don't always track surgeon volume, which is one of the limitations why it probably hasn't been done before. I think the key is getting a lot of people in this audience together and seeing what our own data is. Unfortunately, probably most of the people in this room are high volume surgeons, and in order to do some of these studies well, I think we need to get the low volume surgeons involved as well. Thank you.

Presented at the 49th Annual Meeting of the Society for Surgeons of the Alimentary Tract at Digestive Disease Week, May 17–21, 2008, San Diego, CA, USA

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Eppsteiner, R.W., Csikesz, N.G., Simons, J.P. et al. High Volume and Outcome After Liver Resection: Surgeon or Center?. J Gastrointest Surg 12, 1709–1716 (2008). https://doi.org/10.1007/s11605-008-0627-3

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