Differential association of the 5-factor modified frailty index with postoperative pulmonary complications: specific prediction of infection risk after pulmonary lobectomy.

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; 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.