Objective  To investigate the relationship between diaphragmatic dysfunction and postoperative pulmonary complications (PPCs) following thoracoscopic lung resection, and to assess the value of postoperative diaphragmatic excursion (DE) measured during quiet breathing in the early identification of PPCs.

Methods  This was a single-center, exploratory study conducted at Nanjing Drum Tower Hospital, Affiliated Hospital of Medical School, Nanjing University from April to December, 2024. Patients undergoing thoracoscopic lung resection were enrolled and divided into a PPCs group and a non-PPCs group based on the occurrence of postoperative pulmonary complications. General patient information, comorbidities, surgical data, lung ultrasound (LUS) scores, and diaphragmatic ultrasound parameters were collected. The diaphragmatic ultrasound parameters included diaphragmatic thickening fraction (DTF) and diaphragmatic excursion (DE) measured on the first postoperative day, and ipsilateral diaphragmatic parameters were derived according to the surgical side. Postoperative ipsilateral diaphragmatic ultrasound variables were compared between the PPCs and non-PPCs groups. Least absolute shrinkage and selection operator (LASSO) regression was used to screen for variables associated with PPCs, and a multivariate model was then established using Firth logistic regression. Receiver operating characteristic (ROC) curves were employed to evaluate the predictive performance of postoperative ipsilateral DE during quiet breathing for PPCs.

Results  A total of 117 patients were enrolled, of whom 21 (17.9%) developed PPCs within 30 days postoperatively. In patients with PPCs, the ipsilateral DE on the first postoperative day was 0.91 (0.84, 1.12) cm, lower than 1.20 (1.03, 1.41) cm in those without PPCs (P ＜ 0.001). LASSO regression identified six candidate variables associated with PPCs: hypertension, wedge resection, postoperative LUS score, first-postoperative-day DTF, DE, and the decrease in DTF. Firth logistic regression revealed that wedge resection and first-postoperative-day DE were both associated with a decreased risk of PPCs OR = 0.227 (95% CI: 0.065–0.710, P = 0.010) and OR = 0.042 (95% CI: 0.002–0.436, P = 0.005), respectively. ROC curve analysis showed that first-postoperative-day DE predicted PPCs with an AUC of 0.773 (95% CI: 0.657–0.890, P ＜ 0.001). The optimal cutoff value was 0.925 cm, yielding a sensitivity of 66.7%, a specificity of 89.6%, a positive predictive value of 58.3%, and a negative predictive value of 92.5%.

Conclusion  Ipsilateral diaphragmatic dysfunction after thoracoscopic lung resection is closely associated with PPCs, and postoperative ipsilateral DE serves as an important early identification indicator. Bedside diaphragmatic ultrasound monitoring facilitates early screening of high-risk patients.