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: > 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.