The cases in this study were sourced from the Department of Thoracic Surgery, Fourth Hospital of Hebei Medical University from April 2023 to October 2024. The included patients were diagnosed with pulmonary nodules or lung space-occupying lesions via chest CT and clinically diagnosed with either lung cancer or “pending investigation of the nature of lung space occupying lesions.” Following thoracic surgery evaluation, they were deemed eligible for lung resection surgery. The inclusion criteria were: (1) aged over 18; (2) had undergone bronchoscopy biopsy or percutaneous lung biopsy and been diagnosed with lung cancer by histopathology, or the nature of the lung space-occupying lesion was to be investigated; (3) the indications for lung resection surgery were clear after clinical judgment; (4) voluntarily completed CPET and signed the informed consent forms before surgery; (5) underwent lung resection for the first time; and (7) complete information.

The exclusion criteria were as follows: (1) individuals with mental disorders and motor disorders; (2) individuals with unstable vital signs before surgery; (3) individuals with various infections, acute metabolic disturbances, or other severe complications before surgery; (4) individuals with a history of cerebral infarction, myocardial infarction, or surgical procedures in the past three months before surgery; (5) individuals diagnosed with malignant tumors other than lung cancer; (6) individuals with absolute contraindications for CPET; and (7) individuals with incomplete information.

The study was approved by the Ethics Committee of the Fourth Hospital of Hebei Medical University (approval number 2025KS101).

The personal information and clinical data of the patients according to inclusion criteria were collected. All included patients underwent CPET within one week before surgery. Preoperative transthoracic echocardiography was routinely performed to assess cardiac structure and function. Baseline cardiovascular history, including arrhythmia, coronary heart disease, and deep vein thrombosis, was documented. Patients did not have to discontinue any daily medication before the CPET examination.

CPET was conducted using a MasterScreen-CPX cardiopulmonary exercise assessment system (Jaeger, Germany) in the symptom-limited maximal incremental CPET exercise mode. The following indicators were collected from the CPET examination: reason for termination of exercise; the percentage of maximal workload at termination relative to the predicted value (maximal workload %pred), peak oxygen uptake (peak VO₂), the percentage of peak oxygen uptake relative to the predicted value (peak VO₂%pred), the percentage of anaerobic threshold relative to the predicted value (AT %pred), peak heart rate (peak HR), peak metabolic equivalent (peak MET), peak respiratory exchange ratio (peak RER), blood pressure (BP) at rest/peak time, the ventilatory equivalent for carbon dioxide (VE/VCO₂ slope), and the ventilatory equivalent for carbon dioxide at the anaerobic threshold (VE/VCO₂@AT).

The indications for immediate termination of exercise were as follows: (1) newly emerging or worsening angina pectoris, or dyspnea; (2) ST segment elevation ≥1.0 mm in leads without diagnostic Q waves (excluding V1 and aVR leads); ST segment depression ≥2.0 mm or downsloping depression during exercise, or significant axis deviation; (3) central nervous system symptoms such as ataxia or dizziness, or signs of impending syncope (presyncope); (4) peripheral hypoperfusion such as cyanosis or pallor; (5) symptoms such as fatigue, shortness of breath, wheezing, leg cramps, or muscle and joint pain that prevent continuation of exercise; (6) a decrease in exercise systolic blood pressure ≥10 mmHg compared to the resting state, or an excessive hypertension response; and (7) severe arrhythmias, including sustained ventricular tachycardia, frequent ventricular premature beats, frequent supraventricular tachycardia, frequent paroxysmal ventricular tachycardia, frequent conduction block, or frequent bradyarrhythmias.

The postoperative complications and follow-up information after discharge of these patients within 30 d postoperatively were collected. The occurrence and prognosis of postoperative cardiopulmonary complications were documented and analyzed, and the correlations between the occurrence of postoperative cardiopulmonary complications and preoperative statistical indicators were investigated.

The cardiorespiratory complications occurring within 30 d postoperatively were recorded. Respiratory complications included: (1) re-intubation or the inability to extubate postoperatively, necessitating transfer to the ICU for mechanical ventilation due to respiratory failure; (2) chest tube duration ≥ 7 d due to prolonged air leak, atelectasis, pleural effusion, etc. (14, 15); (3) pulmonary infection accompanied by changes visible on chest x-ray or chest CT scan; (4) respiratory distress syndrome; and (5) pulmonary embolism. Cardiovascular complications included: (1) myocardial infarction; (2) angina pectoris; (3) heart failure; and (4) arrhythmias requiring treatment. The occurrence of complications was defined as the presence of one or more of the above.

Statistical analysis was conducted using SPSS 27.0 software. Categorical data were expressed as percentages, while quantitative data were expressed as mean ± standard deviation (x ± s). Chi-square test was employed to compare categorical data. For quantitative data adhering to a normal distribution, independent-sample t-test was used for inter-group comparisons. Mann–Whitney U test was applied for inter-group comparisons of measurement data that did not follow a normal distribution. The CPET indicators with significant differences were stratified and subjected to logistic regression analysis. Statistical significance was indicated by P < 0.05. The sensitivity and specificity of each indicator were also evaluated.

We included a total of 397 patients who met the inclusion criteria and were diagnosed with either lung cancer or pulmonary nodules/pulmonary space-occupying lesions requiring surgical intervention. All patients underwent preoperative CPET. Based on the clinical diagnosis and disease stage, thoracic surgeons performed various types and extents of lung resections: 376 patients underwent video-assisted thoracoscopic lung resection (lung wedge resection/segmentectomy/lobectomy with or without lymph node dissection); 19 patients underwent thoracotomy (e.g., conversion from thoracoscopy to open-chest lung resection and thoracotomy with lung resection and lymph node dissection); and two patients underwent total pneumonectomy combined with lymph node dissection. The 21 patients were excluded due to the small number of patients undergoing thoracotomy or total pneumonectomy. Consequently, 376 patients who underwent video-assisted thoracoscopic lung resection were included in the final statistical analysis. The included cases included 162 males and 214 females with a mean age of 62.5 ± 6.1 years.

The postoperative complications were followed up for 30 d, and 52 patients experienced at least one complication. The incidence of cardiorespiratory complications was 13.8%, with a total of 56 occurrences of seven types of complications. There were no fatalities. The frequency of each type of complication is detailed in Table 1.

Comparison between the subgroup without cardiopulmonary complications (NCCP group: 324 cases) and the subgroup with cardiopulmonary complications (CCP group: 52 cases) revealed statistically significant differences in age, extent of lung resection, and lymph node metastasis (P < 0.05); no significant differences between the two groups were observed in other general conditions (P > 0.05). Regarding the CPET indicators, statistically significant differences were observed in peak HR, peak VO₂, peak VO₂%pred, peak MET, and maximal workload %pred between the two groups (P < 0.05). In contrast, no statistically significant differences were found in AT %pred, VE/VCO₂@AT, VE/VCO₂ slope, and peak RER between the two subgroups (P > 0.05). The comparison of general conditions and CPET data between the two subgroups is detailed in Table 2.

The indicators exhibiting significant differences between the NCCP and CCP groups following thoracoscopic lung resection were divided into distinct levels. For example, peak VO₂ was divided into <20 mL/(min·kg), <15 mL/(min·kg); peak VO₂%pred was divided into <80%, <70%, <60%; peak MET was divided into <6, <5, <4; and maximum workload %pred was divided into <80%, <70%, <60%. The incidence of complications at these indicator levels was then compared between the two subgroups. Chi-square test and logistic regression analysis were performed, and the indicators without statistical significance (P > 0.05) were eliminated. The results are shown in Table 3.

Based on the findings of Section 3.2, the indicator cut-off values resulting in significant differences between the NCCP and CCP groups were analyzed to evaluate the sensitivity, specificity, positive predictive value, and negative predictive value of these parameters at various cut-off levels in predicting postoperative cardiopulmonary complications. As shown in Table 4, the sensitivity and specificity of peak VO₂%pred <70%, peak MET <5, and maximal workload %pred <80% both exceeded 60%, with the negative predictive values exceeding 90%. The positive predictive values of peak VO₂ < 15 mL/(min·kg), peak VO₂%pred <60%, peak MET <4, and maximal workload %pred <60% all exceeded 30%. The diagnostic accuracy and odds ratios (ORs) obtained by categorizing the indicators based on these thresholds are presented in Table 5. The diagnostic accuracy was highest using the following cutoff values of peak VO₂ [15 mL/(min·kg)], peak VO₂%pred (60%), peak MET (4), and maximal workload %pred (60%), resulting in ORs of 6.2, 4.0, 4.6, and 3.2, respectively.

Early screening for lung cancer enables early lesion detection, thereby reducing the scope of surgical resection and allowing the application of thoracoscopic surgical approaches. Thus, early screening significantly reduces the occurrence of postoperative complications and allows some elderly lung cancer patients who cannot tolerate thoracotomy to receive radical treatment. Due to the limited number of cases with large resection scope and thoracotomy, these patients were excluded from the study, leading to a certain bias. In addition, the overall condition and cardiopulmonary function of the enrolled patients in this study were generally good. The conditions of some patients were classified as contraindications because of old age, poor general condition, and poor cardiac and/or pulmonary function with obvious clinical symptoms. Others declined testing because they were unable to cooperate. As a result, few patients with poor CPET indicators were included. Intraoperative variables such as operative duration and intraoperative complications were not included in the analysis. These factors may independently contribute to postoperative complications and should be considered in future studies. Future research is needed that includes more patients with large lung resection scopes and poor cardiopulmonary function, providing a more comprehensive reference for the prediction of complications after lung resection.