Before obtaining the results of our study, SAS or mSAS was a predictor for surgical morbidity in patients who received surgery for gastric cancer. However, it remains unclear whether this is confirmed in the patients who received neoadjuvant chemotherapy followed by surgery. However, this study could not show the utility of the SAS or the mSAS in predicting postoperative complications in these patients. The mSAS was not an independent predictor of morbidity. As long as we know, this present study is the first report to evaluate the correlation between the SAS and complications in patients treated with NAC followed by radical gastrectomy.
Thus far, some previous studies have demonstrated the SAS’s utility in predicting complications (9, 10), other studies reported 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 risk factors for complications in the present study. In this study, high BMI, DM, and long operation time were identified as independent risk factors for postoperative complications. In the low mSAS group, the proportions of patients with high BMI and a long operation time were higher in comparison to 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 high BMI or a long operation time.
Anesthesia may have also influenced the results. LHR and LMAP, which are included in the SAS and mSAS, can easily be affected by anesthesia. Deep anesthesia can reduce arterial pressure without any bleeding. The use of high doses of opioids could prevent an increase in the heart rate caused by bleeding or dehydration. Theoretically, the mSAS should be evaluated with the same conditions of anesthesia. Unfortunately, anesthesia in our institution was managed by several doctors with different policies during the study period. The lack of statistical significance of the SAS and mSAS in predicting complications might have been influenced by these different managements.
This present study and the previous study by Miki et al. (12), reported that the mSAS significant predicted morbidity in patients undergoing primary surgery have some differences. First, the EBL of our population was much higher than that of their population. This could be explained by surgical difficulties, such as fibrosis induced by NAC or extensive lymphadenectomy, which was selected in more than half of the present cohort. These differences of the study population might lead to different result from the previous study. Second, our cutoff value of mSAS was much higher than the previous report, even though our EBL was higher. This might have been due to the very high incidence of complications in the present population. This point might be another reason to make discrepancy between our study and the previous one as well.
In this study, high BMI, DM, and 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). High BMI is closely related to excessive visceral fat which may extend the operation time and impair lymph node dissection (24, 25), increasing the difficulty of the whole operation. Excessive visceral fat easily induces metabolic syndrome, including DM, which makes patients more susceptible to infection and which can inhibit wound healing. And long operation time has been reportedly 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.
This study included some limitations to be noted. First, this present study was a retrospective, single-center study. Although this study population was mostly limited to patients in prospective clinical trials, the possibility of several biases was not completely excluded. Moreover, we cannot deny the possibility of type 2 error in this study because of small sample size. From this point, a study of large sample is expected. A prospective study with a large sample size is needed to confirm our results. Second, the sample size was small, therefore 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. Future prospective study with large sample size is necessary to confirm the present results.