Before obtaining the results of our study, SAS and mSAS have been considered predictors for surgical morbidity in patients who receive surgery for gastric cancer. However, whether or not this remains true in patients who receive neoadjuvant chemotherapy followed by surgery is unclear. Unexpectedly, this study failed to demonstrate the utility of the SAS or mSAS for predicting postoperative complications in this patient population. The mSAS was not an independent predictor of morbidity. To our knowledge, this study is the first report to evaluate the correlation between the SAS and complications in patients treated with NAC followed by radical gastrectomy.
Several previous studies have demonstrated the utility of SAS for predicting complications (9, 10), although other studies have described the usefulness of the mSAS but not the SAS (12, 14). The utility of the SAS seems to depend on the type of surgery or the characteristics of the cohort. We considered the reasons why the SAS and mSAS were not found to be risk factors for complications in the present study. In our study, a high BMI, the presence of DM, and a long operation time were identified as independent risk factors for postoperative complications. In the low mSAS group, the proportions of patients with a high BMI and long operation time were higher than in the high mSAS group, suggesting that these factors were confounders of the mSAS. These results suggested that patients with a high BMI or longer operation time easily develop surgical morbidities and that the predictive value of the mSAS was inferior to that of a high BMI or long operation time.
Anesthesia may also have influenced the results. The LHR and LMAP, which are included in the SAS and mSAS, can easily be affected by anesthesia. Deep anesthesia can reduce the arterial pressure without any bleeding, and the use of high doses of opioids can prevent an increase in the heart rate caused by bleeding or dehydration. Ideally, the mSAS should be evaluated under the same conditions of anesthesia. Unfortunately, however, anesthesia in our institution was managed by several doctors under different policies during the study period. The lack of statistical significance of the SAS and mSAS for predicting complications might therefore have been influenced by these different management approaches.
This study and Miki’s (12) study differ in some respects, although both studies investigated the predictive value of the mSAS in gastric cancer patients. First, the EBL of our population was much higher than that in Miki’s study, possibly due to surgical difficulties, such as fibrosis induced by NAC or extensive lymphadenectomy, which was selected in more than half of the present cohort. These differences might have caused our results to differ from those of Miki’s study. Second, our cut-off value of mSAS was much higher than that in the previous report, even though our EBL was higher, possibly due to the very high incidence of complications in the present population. This point might be another reason for the differences between the present and previous study.
In this study, a high BMI, the presence of DM, and a long operation time were detected as risk predictors for postoperative complications in patients treated with NAC. These factors are well known predictors of complications in primary surgery (20-23). A high BMI is closely related to excessive visceral fat, which may extend the operation time and impair lymph node dissection (24, 25). Thus, a high BMI increases the difficulty of the whole operation. Excessive visceral fat easily induces metabolic syndrome, including DM, which makes patients more susceptible to infection and can inhibit wound healing. A long operation time has been reported to be a risk factor of postoperative complications, accelerating the speed of body metabolism and increasing the consumption of nutrition (22). These factors would not be changed after NAC.
Several limitations associated with the present study warrant mention. First, this was a retrospective, single-center study. Although our study population was mostly limited to patients enrolled in prospective clinical trials, the possibility of several biases could not be completely excluded. Furthermore, we cannot deny the possibility of type 2 error in this study because of the small sample size. For these reasons, a prospective study with a large sample size is needed to confirm our results. Second, the sample size was small, so the predictive value of the mSAS might have been underestimated in this study.
In conclusion, the predictive value of SAS or mSAS for morbidity may be limited in patients who undergo gastric cancer surgery after NAC. A prospective study with a large sample size will be needed to confirm the present results.