Abstract:Objective To investigate the effects of sub - anesthetic dose esketamine on oxidative stress markers and postoperative delirium（POD）in patients undergoing laparoscopic radical resection for colorectal cancer，so as to provide a reference for the selection of clinical anesthesia regimens. Methods A total of 201 patients who underwent radical resection for colorectal cancer at Taizhou People 's Hospital Affiliated to Nanjing Medical University from January 2021 to December 2024 were retrospectively enrolled and divided into a control group （n=110）and an observation group（n=91）according to anesthesia methods. The control group received conventional general anesthesia induction；the observation group received a single intravenous injection of esketamine（0.3 mg/kg）during anesthesia induction，with other drugs and doses identical to those in the control group. After 1∶1 propensity score matching（PSM），61 patients were included in each group. The two groups were compared in terms of anesthesia effects（onset time of anesthesia，onset time of muscle relaxation，spontaneous respiration recovery time，orientation recovery time），levels of neurological function - related indicators［lipoprotein - associated phospholipase A2（LP - PLA2），neuron -specific enolase（NSE），central nervous system - specific protein β（S100β），brain - derived neurotrophic factor（BDNF）］and oxidative stress markers［malondialdehyde（MDA）and superoxide dismutase（SOD）］at baseline（T0），postoperative day 1（T1）and postoperative day 2（T2），as well as the incidence of adverse reactions including POD.Results The observation group had significantly shorter onset time of anesthesia，onset time of muscle relaxation，spontaneous respiration recovery time and orientation recovery time than the control group（P<0.05）. In both groups，BDNF and MDA levels at T1 and T2 were significantly lower than those at T0，while SOD，LP-PLA2，S100β and NSE levels were significantly higher than those at T0（P<0.05）. At T1 and T2，the observation group showed significantly lower MDA，LP-PLA2，S100β and NSE levels，and significantly higher SOD and BDNF levels than the control group（P<0.05）. There were no significant inter - group differences in the incidence of nausea and vomiting，emergence agitation and respiratory dysfunction（P>0.05）. The observation group had significantly lower incidences of POD（13.11%vs 34.43%，χ²=7.645，P<0.01）and sore throat（1.64% vs 16.39%，χ²=8.093，P<0.01）than the control group. Compared with the control group，the observation group also had a significantly lower POD severity score（3.25±1.17 vs 4.86±1.15，t=3.347，P<0.01）and shorter POD duration［（1.13±0.35）d vs（2.90±0.30）d，t=13.585，P<0.01］. Conclusion Sub-anesthetic dose of esketamine，administered after general anesthesia for laparoscopic radical resection of colorectal cancer，resulted in better anesthesia recovery quality，lower POD incidence，reduced oxidative stress，and more favorable improvements in neurological function-related indicators.