Objective: The aim of this study was to investigate the incidence and risk factors of postoperative delirium (PD) in elderly patients after general or gastrointestinal surgery. Summary of Background Data: Societies worldwide are rapidly aging and the number of surgeries in elderly patients has been increasing. PD, which adversely influences postoperative course, has thus become more common. Methods: The Surgery and Anesthesia Network Group of the National Hospital Organization in Japan conducted this retrospective cohort study of patients aged over 70 years who underwent general or gastrointestinal surgery. Results: A total of 219 patients from 9 participating institutes underwent surgery between July 2013 and August 2014. We excluded 2 patients who died within 2 weeks after surgery. Of the remaining 217 cases, 31 (14.3%) developed PD. These patients were older (80 vs. 76 years, P = 0.013), more likely to be male (74.2 vs. 54.8%, P = 0.039), and had higher American Society of Anesthesia Physical Status scores than those without PD. Emergency surgery was more common than elective surgery in the PD group (41.9 vs. 10.2%, P < 0.0001). Multivariate analysis showed that male gender (odds ratio, 3.31; 95% confidence interval, 1.32-9.39; P = 0.0098) and emergency surgery (7.47; 2.79-20.83; P < 0.0001) were independent risk factors of PD. Conclusions: The incidence of PD was high in male patients and those undergoing emergency surgery. Effective interventions in these groups will be necessary to improve treatment outcomes in elderly patients. (UMIN R000022185)

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