Supplementary Material for: The 'Weekday effect' on Enhanced Recovery After Surgery Protocol for Gastrectomy

Introduction: While Enhanced Recovery After Surgery (ERAS) protocol demonstrated to improve outcomes after gastrectomy, some papers evidenced a detrimental effect on postoperative morbidity related to the "weekday effect". We aimed to understand whether the day of gastrectomy could affect postoperative outcomes and compliance with ERAS items. Methods: We included all patients that underwent gastrectomy for cancer between January 2017 and September 2021. Cohort was divided considering the day of surgery: Early group (Monday-Wednesday) and Late group (Thursday-Friday). Compliance with protocol and postoperative outcomes were compared. Results: 227 patients were included in Early group, while 154 in Late group. The groups were comparable in pre-operative characteristics. No significant difference in pre/intraoperative and postoperative ERAS items' compliance was apparent between Early and Late groups, with most items exceeding the 70% threshold. Median length of stay was 6.5 days and 6 days in Early and Late groups (p=0.616), respectively. Morbidity was 50% in both groups, with severe complications that occurred in 13% of Early patients and 15% of Late patients. Ninety-day mortality was 2%, and it was similar between the two groups. Conclusions: In a Center with a standardized ERAS protocol, the weekday of gastrectomy has no significant impact on the success of each ERAS item and on postoperative surgical and oncological outcomes.