Identifying risk factors and pathogens in postoperative pneumonia after lung surgery for cancer: a retrospective cohort study

Background: Postoperative pneumonia (PoP) is a significant complication that can arise after lung resection surgery, affecting between 1.5% and 12% of patients. This condition can result in serious consequences, including respiratory failure, extended hospital stays, and increased mortality rates. This study aimed to identify clinical and surgical risk factors for PoP and characterize the microbiological profile of infections in patients undergoing lung cancer surgery. Methods: A retrospective observational study was carried out involving 750 adult patients who underwent lung cancer surgery from 2017 to 2019 at the Thoracic Surgery Unit of IRCCS Humanitas Research Hospital. The study analyzed data on patient demographics, comorbidities, preoperative lung function, surgical details, and postoperative outcomes. The primary endpoint was the occurrence of PoP, which was defined based on radiological and clinical criteria occurring between 72 hours and postoperative day 7. Results: PoP was observed in 79 patients, representing 10.7% of the cohort. Identified risk factors for PoP included smoking, low preoperative lung function [measured by forced expiratory volume in 1 second (FEV1) and diffusing capacity of the lungs for carbon monoxide (DLCO)], chronic obstructive pulmonary disease (COPD), asthma, diabetes, a high American Society of Anesthesiologists (ASA) score, advanced cancer stages (III-IV), squamous cell carcinoma, and the use of neoadjuvant chemotherapy. Surgical risk factors included the use of open thoracotomy and the conversion from video-assisted thoracoscopic surgery (VATS)/roboticassisted thoracoscopic surgery (RATS) to open thoracotomy. Patients who developed PoP experienced significantly worse postoperative outcomes, including higher rates of respiratory failure, longer hospital stays, and extended chest tube duration. In 87.3% of PoP cases, bronchoscopy with bronchoalveolar lavage was performed, revealing Escherichia coli (E. coli) and Pseudomonas aeruginosa as the most frequently identified pathogens. Conclusions: PoP is a common and clinically impactful complication after lung cancer surgery. Independent risk factors identified include asthma, higher ASA score, and conversion to thoracotomy. Endoscopic evaluation with microbiological sampling proved valuable for early diagnosis and targeted therapy. These findings support the implementation of optimized preoperative assessment, surgical planning, and multidisciplinary management strategies to reduce PoP incidence and improve clinical outcomes.