Abstract: Objective To investigate the occurrence of postoperative delirium in elderly patients undergoing radical resection of colorectal cancer and analyze its related risk factors.Methods A retrospective study was conducted involving 267 elderly patients who underwent elective radical resection for colorectal cancer at our hospital from June 2024 to October 2025.According to whether delirium occurred within 3 days after surgery, the patients were divided into a delirium group and a non-delirium group.Multivariate Logistic regression analysis was used to determine independent related factors.A regression prediction model was constructed.Receiver operating characteristic (ROC) curve of this model was drawn, and its discriminative ability was evaluated by area under the curve.Internal validation was performed using Bootstrap method.Concordance index was used to evaluate model discrimination, calibration plot was used to evaluate calibration, and clinical decision curve was used to evaluate the clinical practicability of the model.Results The incidence of delirium within 3 days after surgery in elderly patients undergoing radical resection of colorectal cancer was 16.10% (43/267).Multivariate Logistic regression analysis showed that preoperative modified Frailty Index-5 (mFI-5), preoperative C-reactive protein/albumin ratio, intraoperative hypothermia, and anesthesia time were independent risk factors for postoperative delirium in elderly patients undergoing radical resection of colorectal cancer (P<0.05).A Logistic regression prediction model was established based on the above factors: Logit(P) =-16.152+0.991×preoperative mFI-5 score(≥2 points=1, <2 points=0)+0.257×preoperative C-reactive protein/albumin ratio (%) + 1.225 × intraoperative hypothermia (no=0, yes=1)+0.022×anesthesia duration (min).The ROC curve demonstrates that the model achieves an area under the curve (AUC) of 0.908 for predicting the incidence of postoperative delirium in elderly patients undergoing radical resection for colorectal cancer.The C-index after internal validation of the model obtained by Bootstrap method was 0.917.Calibration curve showed high consistency between the ideal probability curve and the actual probability curve, with a mean absolute error of 0.039.Decision curve showed that when the threshold probability was 0.1-0.9, clinical benefit was high.Conclusion The incidence of postoperative delirium is high in elderly patients undergoing radical resection of colorectal cancer.The occurrence of postoperative delirium is related to preoperative frailty, C-reactive protein/albumin ratio, intraoperative hypothermia, and anesthesia time.The regression prediction model constructed accordingly has good predictive value.

Key words: colorectal cancer; elderly; postoperative delirium; risk factors