Abstract
BACKGROUND: Frailty is recognized as an important predictor of postoperative outcomes, yet evidence on the differential association between the 5-factor modified frailty index (mFI-5) and specific postoperative pulmonary complications (PPCs) following pulmonary lobectomy remains limited. This study aims to investigate the association between mFI-5 and the risk of distinct PPCs, with comprehensive adjustment for potential confounders. METHODS: In this retrospective study of 391 patients undergoing lung resection, participants were stratified into Robust, Pre-frail, and Frail groups by mFI-5 score. The primary outcomes were postoperative pulmonary infection, pneumothorax, and pleural effusion, defined according to EPCO criteria with thoracic surgery-specific refinements. Multivariable logistic regression was used to assess associations, adjusting for comprehensive confounders. Multicollinearity was assessed using variance inflation factor (VIF). Subgroup analyses and interaction tests were performed. RESULTS: Among the cohort (mean age 62.17 ± 8.71 years, 61.13% male), frailty status was associated with older age and a higher comorbidity burden. In fully adjusted models, the mFI-5 was a strong, independent predictor of postoperative pulmonary infection. Compared to the Robust group, the Pre-frail and Frail groups had significantly increased odds, with adjusted odds ratios (ORs) of 3.5 (95% CI: 1.6-7.9; P = 0.002) and 7.3 (95% CI: 2.0-26.2; P = 0.002), respectively. In contrast, no significant association was found between frailty and postoperative pneumothorax or pleural effusion (all P > 0.05). Subgroup analyses suggested that the risk of infection might be more pronounced in males and smokers, and that smoking history and surgical site might modify the associations with pneumothorax and effusion, respectively. CONCLUSION: The 5-factor modified frailty index (mFI-5) was independently associated with an increased risk of postoperative pulmonary infection, but not with pneumothorax or pleural effusion, following lung surgery. These findings suggest that the predictive capacity of mFI-5 varies across complication types.