Background: Frailty and cognitive impairment are well-known risk factors of delirium after cardiac surgery. Frailty is closely associated with cognitive impairment. This study aimed to examine how frailty and cognitive impairment affect the incidence of delirium after cardiac surgery in older patients. Methods: In total, 89 patients (aged ≥65 years) who underwent cardiac surgery between April 2016 and December 2017 were included (74.9 ± 5.5 years, male 64.1%). They were divided according to the combination of frailty and mild cognitive impairment (MCI): Group 1, non-frailty and non-MCI; Group 2, non-frailty and MCI; Group 3, frailty and non-MCI; and Group 4, frailty and MCI. Frailty was defined as a score of at least 3 points according to the Japanese version of the Cardiovascular Health Study criteria, and MCI was defined as a Montreal Cognitive Assessment score less than 26. Delirium was evaluated using the Intensive Care Delirium Screening Checklist, and a score of 4 or higher indicated delirium. Multivariate logistic regression analysis was performed to examine the influence of the combination of frailty and MCI on delirium after cardiac surgery. Results: In total, 31 patients (34.8%) showed postoperative delirium. Multivariate analysis-adjusted baseline characteristics (reference, Group 1) showed that only Group 4 had a risk of delirium after cardiac surgery (odds ratio, 7.494; 95% confidence interval 1.539–36.494). Conclusion: Preoperative coexistence of frailty and MCI poses the greatest risk of delirium after cardiac surgery. Therefore, attention should be paid to both physical and cognitive function prior to surgery. Further studies are warranted to investigate the optimal intervention for high-risk patients.
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