ObjectiveTo investigate the effect of omega-3 polyunsaturated fatty acids on delirium in elderly patients after taking gastric cancer surgery.MethodsA prospective study was conducted. Elderly patients with gastric cancer undergoing radical gastrectomy in West China Hospital of Sichuan University from June 2015 to June 2018 were divided into experimental group and control group for the purpose of research. All patients were operated by the same group of surgeons and anesthesiologists. Patients in the experimental group received intravenous infusion of 10% fish fat emulsion (Ewing) 100 mL daily from the first day after operation extra to routine treatment; patients in the control group received routine treatment after operation. The postoperative delirium, inflammation, complications, hospital stay, andre-admission on 30 days were compared between the two groups.ResultsA total of 205 patients were under research. The results were as follows. ① There were 47 delirium patients in the control group and 22 delirium patients in the experimental group. The difference between the two groups was statistically significant (P<0.001). There were 32 cases and 19 cases discovered with delirium in the control group and the experimental group during 1-3 days after operation; there were 19 cases and 6 cases were detected with delirium in the control group and the experimental group during 4-7 days after operation, respectively. The difference was considered statistically significant (P<0.05). ② Inflammation indexes of the experimental group were significantly lower than those of the control group on the 3rd and 7th day after operation, including count of WBC, C-reactive protein, interleukin-6, tumor necrosis factor-α, and platelet crit, and the difference were statistically significant (P<0.05). ③ Postoperative fever occurred in 46 patients in the experimental group, while 71 patients in the control group. The difference was statistically significant (P<0.01). ④ There were 2 cases of incision liquefaction in the control group and 1 case of mild chylous leakage in the experimental group. There was no significant difference in incision liquefaction rate and chylous leakage rate between the two groups (P>0.05). ⑤ The average hospitalization time of the experimental group was shorter than that of the control group ［(8±1) d vs. (9±2) d］. The difference was considered statistically significant (P<0.01).Conclusionω-3 polyunsaturated fatty acids can reduce postoperative delirium and improve short-term prognosis in elderly patients with gastric cancer by controlling inflammation and stress response.