Editorial commentToward quality improvement of thoracic aortic surgery: estimating volume–outcome effect from nationwide survey

Since the first report dealing with the surgical volume–outcome relationship published 3 decades ago by Luft and co-workers in the NEJM [1], a great number of articles have addressed this issue. Whatever the studied surgical specialty, they have generally concluded that this relationship exists and that it is in favour of the high volume structures. In cardiovascular surgery, such studies have been most often focussed on coronary artery bypass grafting as, indeed, it has represented for decades the largest cohorts of patients and the most frequent procedures performed in most centres as well as by each individual surgeon. In their article entitled ‘Toward quality improvement of thoracic aortic surgery: Estimating volume outcome effect from nationwide survey’, Miyata and co-workers extend this issue to the results of thoracic aortic surgery and analyse the relationship between those results and the hospital surgical volume as well as the individual surgeon volume in Japan [2]. The same group had recently published a similar article on coronary surgery, in which they concluded that ‘In Japan, high-volume compared to low-volume providers had better outcomes…’ [3]. Using the same methodology and database in the present study, they demonstrate and conclude similarly that hospital thoracic aortic surgery volume is linked to statistically significant decreases in both operative and 30-day mortality rates, but that individual thoracic aortic surgery volume of surgeons is not. As could be expected from this group, among which are class experts in aortic surgery and in quality control, the study is based on solid data and on an appropriate and little questionable statistical analysis. Despite the obvious differences between coronary and thoracic aortic surgeries, those identical results and conclusions seem logical. Although quantitative comparative data concerning thoracic aortic surgery are rather scarce, some recent publications or information reinforce the ‘high volume–better results’ statements. For instance, the German registry of acute aortic dissection demonstrates that, among the participating centres, 12 performed less than 10 cases a year, 12 performed between 10 and 30 cases a year and 17 performed more than 30 cases a year (representing 73% of all cases) with respective mortality rates of 34%, 22% and 14% [4]. In addition, it is easy to observe that large centres treating a high volume of a determined pathology may gather specialised and dedicated teams, develop appropriate care protocols and processes and can count on larger human and financial resources. It is also frequent that the high-volume centres are affiliated to academic structures in which programs of experimental and clinical research as well as teaching allow for permanent care adjustment and technical improvement. It may also seem obvious that the experience of the medical and non-medical staff increases rapidly with the high-volume activity and that unexpected pre-, intra- or postoperative conditions or events are dealt with appropriately and accurately. The present study also ‘shows that the mortality outcomes of high-volume surgeons at high-volume hospitals were similar to those of low-volume surgeons at high volume hospitals’. This apparent paradox is not actually surprising. Even though the experience and skill of individual surgeons may be of some importance in the patients’ outcome, this factor has lost its pre-eminence in favour of the quality of the institutional and team organisation. In modern surgery, the surgeon is only one (although important) element of a complex chain of care processes in which many other individuals (anaesthesiologists, intensivists, nurses and technicians, etc.) have a major role and whose activities and competence are of paramount importance in the quality of the patients’ outcome. In addition, the whole ancillary environment, the presence of and connection with other excellent specialties as well as the easy resort to their competence are often key determinants in solving difficult conditions and can, beyond any doubt, make the difference between success and failure. This might explain why ‘low-volume’ surgeons working in sophisticated high-volume centres may obtain the same satisfactory results as their ‘high-volume’ colleagues. As demonstrated by Huckman and Pisano [5], the same reasons probably explain why successful ‘high-volume’ surgeons in high-volume centres may not maintain their successful results when placed in low-volume institutions. Nevertheless, the present study, as all the previous similar studies, raises a great number of questions. If one looks at the literature as a proper reflection of the surgical activity of centres, it can be easily observed that the centres that report very large numbers of thoracic aortic procedures per year (let us say more than 250 cases, for example) are only a handful in the world. On the contrary, the centres with a mild-to-moderate activity are the majority. Therefore, in most countries, the comparison can be made only between low-volume and intermediate-volume activities. This is perfectly illustrated in the present Japanese study, as 13 centres are doing 12 procedures every year, 14 centres are doing 24 procedures and 9 centres are performing 52 procedures, on average. After adjusting for the risk, the hospital mortality of those three groups varies from 7% to 4% with a rather weak statistical significance and with no difference between the two latter groups. It is interesting to note that these results, including for low-volume centres, are in accordance to what is obtained in other countries of the Western world. Perhaps not intentionally, the authors demonstrate that excellent results can be obtained in non-concentrated systems of care and that low-volume centres may function quite well. Therefore one may conclude that volume itself is a poor indicator of outcomes and, as stated by Sade and co-workers, ‘Volume itself does not lead to good outcomes…it is a proxy measure for other factors that affect care’ [6]. It is also to be observed that all studies dealing with volume–outcomes relationship use mortality as the sole end-point. Outcomes encompass many more features such as immediate morbidity, ICU and hospital stay, mid- and long-term quality of life, late mortality and morbidity rates and, often, rate of re-operations. Is it ascertained that those elements are better in high-volume centres than in low-volume ones? It might be the contrary. For instance, in some high-volume centres, because of the high turnover of the patients and the number of emergencies, the operating theatres might be occupied during a large part of the day and the night increasing the infectious risk. Similarly, because of the necessity of having beds available, the stay in ICU and hospital may be reduced to excessively low limits and the rate of further complications significantly increased. Furthermore, there is no compelling reason why a high-volume centre should systematically apply care processes and protocols of better quality than the ones used in low- or medium-volume centres. On the contrary, it is not rare that, because of their workload, high-volume centres develop unorthodox behaviours and habits. As stated by Shahian and Normand, ‘Countless repetitions of suboptimal practices only reinforce those practices and leads to no improvement whatsoever’ [7]. Last, but not least, centres of cardiac (and thoracic aortic) surgery are not immutable and their activity or reputation is not carved in marble for eternity. Being a high-volume provider and having a high-level referral of patients is not a ‘heaven-sent manna’. All centres are living structures with a dynamic evolution. Because of ageing or retirement of prominent members of their staff, unwise recruitment of their successors, erroneous institutional reforms or policy decisions, etc., some high-volume or high-reputation centres may lose their prominent position rapidly. Conversely, low-volume centres often strive to improve their skill and competence and to increase their activity. The staffs strive for better results and are keen to adopt and implement the best possible care processes. To make it short, all high-volume providers have been, at the beginning, low-volume providers. In addition, if we look at some major technical improvements or breakthroughs made in thoracic aortic surgery in the last 3 or 4 decades, we can observe that they often came from what were considered at the time of their description as low- or, rather, medium-volume centres. For example, complete replacement of the aortic root with a composite valved conduit, deep hypothermic circulatory arrest, retrograde cerebral perfusion, selective antegrade cerebral perfusion, ‘elephant-trunk’ technique, use of adhesives in acute dissection repair, endovascular stent grafting, etc. As stated again by Sade and co-workers: ‘High volume may become low and low volume may become high… we have no way of knowing in advance which large programs have peaked and are moving down the mortality rate scale and which small programs are dynamically moving up the scale’ [6]. The present study is certainly important for the Japanese surgical community and health authorities, since aortic surgery represents 19% of all cardiovascular surgical procedures in that country and because, historically, the hospital organisation has resulted in a great number of cardiac surgical departments (about 550 for a population of 110 million people – one centre for 200 000 inhabitants), many of which have a numerically limited activity. However, even though thoracic aortic surgery is distributed in Japan among many more centres than what is observed, on average, in many other highly economically developed countries, the present study is also important for the whole surgical community as the reported results can most probably be generalised. The authors have the wisdom of not drawing dire conclusions about concentration of the aortic activity and about favouring the high-volume centres at the expense of their low-volume counterparts. Such a concentration (regionalisation?) system is, indeed, favoured by the finance providers and the health policymakers in many countries. They, of course, embrace this concept in order to limit the permanently increasing health costs and to better manage the human resources. It is not surprising, either, that the high-volume centres policy is favoured by our colleagues who head such centres. It is indeed an excellent way of keeping their reputation, their power in many instances, and, most probably, their income. Systematic implementation of such concepts might be harmful to the surgical community, as it would preclude many individuals from developing their knowledge, skill, dedication as well as their ideas for technical improvement. Moreover, it might certainly be somewhat deleterious for the patients who, in addition to expecting proper care management, are often keen to be treated in patient-friendly institutions, surrounded by their loved ones and without the undeniable stress of being transported in an unknown and often indifferent environment. The high-volume policy supporters use volume–outcome statistical studies to demonstrate their point. However, such studies give only a general instant view of a given geographical area and certainly do not reflect the reality. The threshold policy, as advocated by some groups and lobbyists, although apparently logical, might be unrealistic or dangerous and, anyway, should be implemented very cautiously. For instance, the Leapfrog group, a consortium of large employers and health insurance providers in the United States, has defined a minimal threshold of 450 cases of coronary procedures per year to obtain optimal outcomes. Implementing a concentration policy based on such a criterion would result in the closure of about 75–90% of the centres in Western Europe and Japan. Not only would common sense suggest that such a proposition is somewhat unreasonable and that, apparently, coronary surgery in Europe and Japan is not worse than elsewhere, but also such a concept is severely questioned within the American medical community itself [8,9]. The careful analysis of the present study as well as the close scrutiny of the relevant literature demonstrates that the volume–outcome relationship remains an unresolved issue. What is the proper volume required to obtain optimal results? So far, no one can tell. Perhaps, only mandatory collection of all actual results (mortality and morbidity) on a regular basis and their analysis by independent structures (government agencies, professional associations, consultant cabinets, etc.) could give a real and reliable overview of the quality of care and of the care providers. This could possibly help the medical and surgical community as well as the institutional policymakers to set up validated optimal care processes applicable to all centres, whether they are high- or low-volume providers. Until now, this seems to be a far dream in most countries.