This study analyzes how anastomotic leak and perioperative outcomes of patients undergoing anterior rectal resection for cancer are influenced by a significant increase in surgical volume at the same institution.
The main result of this study is the demonstration of a significant reduction in estimated anastomotic leak rate following ARR possibly due to centralization of service within the same Hospital.
A correlation between volume and anastomotic leak rates has been reported in only two other studies in the literature: a metanalysis by Huo et al., including 15446 patients, demonstrated a significant reduction in anastomotic leak rate for rectal surgery with a HR of 0.75 (CI 95% 0.58–0.97) while, on the contrary, in a Dutch series, anastomotic leak was decreased in low-volume Hospitals for T1-3 rectal cancers [37, 38]. Other two notable studies are the large series by El Amrani et al. and Burns et al [39, 40]. The former analyzed 45.569 rectal cancer resections performed in France between 2012 and 2016 and could not demonstrate a correlation between volume and anastomotic dehiscence. The latter identified 109.261 patients undergoing colorectal resection and again no significant association between surgical volume and leak was found. Overall the existing literature is inconclusive on this aspect.
Our study brings new data in favor of a positive volume-outcome correlation in rectal cancer surgery in a single institution. Between January 2006 and November 2016 five surgeons in three surgical units within the same large, tertiary academic center were operating on rectal cancer patients. In November 2016, it was taken the decision to centralize rectal cancer patients to only one surgical unit, with two surgeons performing the procedures. Furthermore, a close collaboration with the local Gastroenterology Units and General Practitioners was started in order to increase colorectal cancer case referral to the unit. Operational preparation and strategic planning helped building strong referral networks and, at the same time, the use of laparoscopy and implement enhanced recovery pathways was promoted.
Patients in the two groups were comparable for what concern known risk factors for anastomotic dehiscence, such us diabetes, smoking attitude, etc. [41–42]. A few confounders may be pointed out but most of them are not expected to influence results significantly. The two cohorts are separated in time and it could be argued that change of practice other than volume might have resulted in the observed results. Yet, leak rates after ARR have been reported unchanged throughout the literature for many years and no reproducible significant improvement was introduced in clinical practice between 2006 and 2020, with the possible exception of indocyanine green, which in any case was not used in this series [43, 44]. The two groups, despite being relatively homogeneous, differ in some respects. A fast-track protocol has been implemented in the second time period (resulting in fact in lower LOS) but it has been widely demonstrated that ERAS has no impact on anastomotic leak [19, 20]. The same can be asserted for laparoscopy, which can reduce other postoperative complications such us surgical site infections, but does not affect dehiscence rate [14–16].
Depth of invasion (T stage) was greater in Group A, suggesting a surgery generally more demanding and more prone to complications in Group A, therefore adding value to the results. Finally, patients in Group B tended to have higher preoperative hemoglobin values and a higher need for transfusions, which may be interpreted as an increased intra- post-operative bleeding. This, indeed, may have favored Group A, as acute anemia is a known risk factor for anastomotic fistula [45, 46]. Yet, this may be justified with improved intra and postoperative surgical and anesthesiological management, referable to increased volume.
As Group A spanned a much smaller number of years than Group B, prediction of estimated leak rate for the years 2021–2023 was needed to render the two groups susceptible to (statistically) more appropriate comparison.
Anastomotic leakage is a very severe complication after ARR, often treated multidisciplinary with a reported rate up to 13.4% in an early phase and around 20% in the long-term . Generally, mortality rate is low and, in our series, we did not report any leak-related mortality even though it has been reported to be up to 20% in some studies [21, 22, 27, 47]. Besides mortality, anastomotic leak has a significant impact on long-term functional outcome with the risks of sphincterial function loss and an unintended permanent stoma rate around 20% and it has a significant impact in quality of life and costs for health system [23–27].
Rationale in favor of case centralization to high volume centers is based on two consideration. First, rectal cancer management is particularly complex in many respects, needing multidisciplinary evaluation, availability of numerous treatment options, specialist nurses, teamwork and possibly research facilities [48–50]. Furthermore, it is often a complex procedure requiring highly skilled surgeons to perform meticulous dissection in the narrow space of the pelvis, using minimally invasive techniques.
On the other hand, the evidence regarding volume/outcome is still too conflicting to draw a conclusion in favor of centralization .
Nevertheless, some evidences in favor of a better outcome in high volume facilities comes from multiple large series and metanalysis. The most relevant finding is a decreased 30-days mortality, which is reported in many series [36, 52, 53]. Overall morbidity is reduced in the series reported by El Amrani et al. ; Baek et al report higher rate of sphincter saving procedures, and Jonker et al. found a higher rate of complete radical resection for T4 cancers [38, 53]. Aquina et al. argues that high volume surgeons in high volume hospitals only obtain the best results . Examples of centralizations in Europe for rectal cancer surgery exists in the Netherlands, Germany, Ireland, Norway, Sweden and Spain [54–58].
Yet, in a Dutch series by Jonker et al., high volume hospitals perform worse than low volume in terms of complications and other equally large series also failed to find any significant differences between low and high-volume centers [11, 38, 59–61].
A big limitation in confronting these studies is the definition of “high volume” as there is no consensus on the cutoff value. Recent UK guidelines specifically on this topic could not define a threshold because evidence is not strong enough to set one, since it would mean to cut out hospitals currently performing fewer procedure without a certain justification .
Another aspect is whether the surgeon rather than the center should be the target of centralization. Although some investigators reported better outcome in high volume surgeons, studies so far have shown a high variation in outcomes with mortality ranging from 0 to 7.7 % suggesting that high volume per se, not supported by adequate structures and investments, could not be sufficient to improve outcome . As a matter of fact, current guidelines recommend treatment in centers that can provide standard of care management including multidisciplinary approach (with dedicated oncologists, radiologists, radiation oncologists, endoscopists, surgeons and specialist nurses) but do not make any recommendation regarding hospital volume .
Overall, this study seems to add new information on the effect of volume on rectal surgery such us reduction in LOS, mean operative time, blood transfusion and need of conversion to open surgery. However, giving the retrospective nature of the study and the different time spam in which the two groups of patients were operated, it cannot be clarified whether these results are in effect due to other factors such as the implementation of ERAS and laparoscopy during the years. It is possible that the increase in volume reduces operative time, need for conversion to open surgery and postoperative blood transfusions; LOS could be correlated to both ERAS and minimally invasive surgery approach [15, 62–67].
However, to the best of our knowledge, this is the first study evaluating effects of surgical volume in rectal cancer perioperative outcomes within the same Hospital. Therefore, it is pioneering in investigating effects of increasing volume in one department, rather than comparing different centers with different contexts, in an effort to isolate volume effect and minimize bias due to sample heterogeneity. Most studies in the literature come from population registry studies, involving many different hospitals and many different surgeons within the same Hospital, assembling a heterogeneous jumble of different practices in pre-, intra- and post-operative care. Patients in this study represent a homogenous group of patients managed in the same institution with uniform practices regarding protocols of treatment (e.g. neoadjuvant therapy), and postoperative management (e.g. early detection of leak with serial blood tests, CT scan with contrast per rectum, conservative management if possible). This potentially eliminates bias of comparing different situations, as is the case with population registries.
Furthermore, although being a study on surgical volume, rather than supporting “centralization” of care to pre-existing high volume units, results from this study embrace the possibility of “potentiation” of surgical units already present to optimize results, in line with the current literature.
Some limitations to this study are acknowledged by the authors. In particular, the retrospective nature of the study limit reliability of results, the number of patients treated is relatively low and the single center experience is not easily generalizable to other centers. Oncologic outcomes have not been analyzed in the present study for lack of sufficient follow up for the most recent cohort of patients.