The provision of standard operating time helps to arrange operating room resources more efficiently. Operating room underutilization and overutilization are both wastes. Improving the predictability of surgical time can enhance the efficiency of surgical resource management and save costs. In our study, there was an association between surgical duration and anastomotic leakage, but we could use BMI and pelvic inlet to predict the operative time. BMI and pelvic inlet are two common parameters that can be easily obtained. We believe that a simple preoperative evaluation to measure them can help to determine more reasonable arrangements for surgeries and to prepare exceptional postoperative management, especially in centers that are short on surgical resources.
Although previous studies have shown that several anatomical markers are associated with surgical difficulty, the results are inconsistent [15–18]. This might be due to the limitations of the selection criteria. The criteria for grading surgical difficulty proposed by Escal  included duration of surgery > 300 min, conversion to open procedure, use of transanal dissection, postoperative hospital stay > 15 days, blood loss > 200 ml, and morbidity (grades II and III). The surgical difficulty grade ranged from 0 to 12, and patients scoring six or higher were considered to have high surgical difficulty. However, we found that the critical value of the criteria varies significantly from center to center. Yamamoto  analyzed the data of 121 patients undergoing minimally invasive rectal surgery and found that the median blood loss was only 30 ml, which is lower than the 200 ml proposed by Escal . Therefore, Yamamoto  changed the threshold for blood loss to 100 ml. Moreover, the median operative time and postoperative hospital stay were 310 minutes and 18 days, respectively, so those criteria were also adjusted accordingly. However, in the studies by Sun  and Chen , the average postoperative hospital stay was 8.0 days and 7.7 days, respectively. As a result, these authors adjusted the standard critical value of postoperative hospital stay to 7 days for analysis. In addition, they defined difficult operations with an overall score greater than 3 points, rather than the six used in the previous study. Although different centers reported adopting Escal’s grading standard, most of them were adjusted, indicating that there were still limitations inherent to this grading standard. In our opinion, the criterion was influenced by many factors, such as the surgeon’s style and behavior, the availability of rapid rehabilitation, and medical resources. Therefore, we thought none of the standards could exactly reflect the surgical difficulty until now. In this study, we compared the differences in surgical time, which could be accurately obtained, between different patients. Moreover, we proposed that individual grouping based on the surgical times of different surgeons would be more beneficial to avoid any bias caused by these factors and to make the result more objective and repeatable.
Anastomotic leakage is one of the most common postoperative complications of rectal cancer. It might prolong the hospital stay, delay chemotherapy, increase the economic burden, and even lead to death in serious cases . In addition, anastomotic leakage was found to be related to increased local recurrence, and decreased overall survival, cancer-specific survival, and disease-free survival .This study showed that an excessively long operative time might increase the risk of anastomotic leakage after rectal cancer surgery, as Qu  reported. Moreover, the operative time was found to be related to obesity and to a small pelvic inlet. Obese patients have thick pelvic fat, which leads to a relatively narrow pelvic cavity that makes the surgery difficult. During the procedure, to fully expose the operative field, repeated hard pulling of the proximal intestinal tube and surrounding tissues of the anastomosis would increase collateral damage, resulting in poor postoperative anastomosis healing. In addition, the small pelvic inlet makes it challenging to insert the stapler into the deep pelvis or requires more stapler firings for rectal transection, which are risk factors for anastomotic leakage .
Obesity was found to be associated with not only increased operative time and blood loss [14, 23, 24] but also with higher rates of anastomotic leakage, surgical site infection (SSI), urinary tract infection (UTI), sepsis, and venous thromboembolism (VTE) [25–27].The increase in visceral obesity volume and mesenteric fat area (MFA) in obese patients makes laparoscopic rectal cancer surgery a unique challenge .In this study, patients had BMIs ranging from 16.2 to 31.4 kg/m2 with a mean value of 24.1 kg/m2, which was lower than that in Western populations. Nevertheless, our results agreed with previous reports that found a positive association between BMI and operative time [13, 29].
On the other hand, studies have shown that the bony structure of the pelvis, such as the depth and length of the sacrum, the pelvic inlet and outlet, and the angle of thepelvis, are independent predictors of the duration of surgery and are used as surrogate markers of TME difficulty [11, 15, 30]. In our results, the univariate analysis found differences in the three bone indices of the pelvic inlet, ischial intertuberous diameter, and pelvic depth, suggesting that a deep and narrow pelvis did affect the duration of surgery. Restricted working spaces directly affect how difficult it is to perform of safe and fast surgeries; in addition, it requires visibility and coordination to be optimized. Moreover, through multivariate analysis, it was found that the pelvic inlet was an independent risk factor, so we should pay special attention to them in rectal resection patients. In our retrospective review of surgical videos of some patients with prolonged surgery, we found that several skills might help to reduce surgical time, such as suspending the uterus or peritoneal reflection, lifting the upper rectum with a string, and wiping the lenses with iodophor to prevent fog. However, what mattered most is the teamwork. We believe that these issues should not be a major problem for professional surgical teams because they have more experience in creating suitable surgical areas and are able to identify and anatomize structures even in a restricted pelvic working space.
Not surprisingly, there were some limitations in this study. This was a retrospective analysis, and operative time was measured from the beginning of anesthesia to the end of the surgery, rather than pelvic anatomy time. However, the selected conditions were strict and excluded patients with high rectal, lateral lymph node cleaning, multivisceral resection, and the use of transanal dissection to minimize the influence of confounding factors. In addition, pelvic measurements in this study were made by a single observer, so it could not provide the quantification of interobserver variability.