Associations between oral frailty, oral microbiota composition, and postoperative delirium in older adult patients

Background: Poor oral health, prevalent among the older adults, can undermine overall health and contribute to frailty. Older adults experiencing oral frailty and dysbiosis potentially face an elevated risk of postoperative delirium. This study aims to explore the influence of oral frailty and changes in oral microbiota composition on occurrence of postoperative delirium in older adult patients undergoing non-cardiac surgery. Methods: A total of 303 older adult patients undergoing non-cardiac surgeries were recruited in the Second Affiliated Hospital of Nanjing Medical University from July 2023 to December 2023. Oral swabs for oral microbiota analyses were collected before surgery. Subsequently, after propensity score matching, 21 samples from patients with postoperative delirium and 21 samples from patients without postoperative delirium were analyzed for oral microbiota. Our primary objective was to determine the association between oral frailty, changes in oral microbiota composition, and the occurrence of postoperative delirium. Results: Oral frailty emerged as an independent risk factor for postoperative delirium [HR = 1.75; 95% CI = (1.04-2.96); p = 0.035]. Additionally, patients with postoperative delirium demonstrated lower oral microbiota diversity, as indicated by a reduced Chao index compared with those without postoperative delirium (p = 0.034). A significant association was also found between the dysbiosis index and postoperative delirium (p < 0.001). ROC analysis revealed a pronounced area under the curve of 0.95 (95% CI: 0.88-1.00) for the dysbiosis index in predicting postoperative delirium. Subsequent Principal Coordinates and Kaplan-Meier analyses affirmed that both beta diversity and the dysbiosis index were significantly correlated with incidence of postoperative delirium, with p-values of 0.002 and <0.001, respectively. Furthermore, the interaction analysis through Cox proportional hazards regression suggested a combined effect of oral frailty and the dysbiosis index on the likelihood of developing postoperative delirium (p = 0.004). Conclusions: Oral frailty and changes in oral microbiota among older adult patients undergoing non-cardiac surgery may influence the incidence of postoperative delirium.