Utility of chronic obstructive pulmonary disease assessment test in perioperative assessment of patients with mild to moderate chronic obstructive pulmonary disease

Introduction

Patients with chronic obstructive pulmonary disease (COPD) have a higher incidence of lung cancer than the general population (1). COPD is a well-known risk factor for postoperative pulmonary complications (PPCs); therefore, a detailed preoperative assessment is needed to identify patients at high risk for PPCs and alternative treatment options should be considered (2-5). The risk of PPCs in COPD may vary based on the severity of symptoms, which are usually assessed using the modified Medical Research Council (mMRC) score or COPD Assessment Test (CAT) in clinical practice. Specifically, the CAT score is a widely used, simple indicator to assess patient’s quality of life and predict acute COPD exacerbations (6). However, few studies have evaluated the correlation between symptom-based scores, including the CAT score, and the incidence of PPCs.

Among several test modalities for evaluation before lung resection, spirometry, and the diffusing capacity for carbon monoxide (D_LCO) are essential tests for predicting postoperative lung functions (5,7). The American College of Chest Physicians guideline recommends that patients with postoperative forced expiratory volume in one second (FEV₁) or postoperative D_LCO between 30% and 60% undergo a stair-climbing test or shuttle walk test (SWT), both of which are indicated for most patients with COPD (7). If the result of the SWT falls below expectation or both postoperative FEV₁ and postoperative D_LCO are <30%, the cardiopulmonary exercise test (CPET) should be performed (8,9). The guideline classifies patients with maximum oxygen uptake (VO₂ max) <10 mL/kg/min or 35% predicted to be at high risk and recommends avoiding lung resection, while considering alternative treatment options because of the high mortality risk (7). After excluding the obviously high-risk group, patients with mild to moderate dysfunction should be evaluated using additional criteria to determine a suitable treatment option (10).

In this study, we aimed to explore the potential relationship between the CAT score and PPC in patients with mild to moderate COPD, a population commonly undergoing lung cancer surgery. Additionally, we compared the predictive values of the CAT score with those of previously well-established predictors of PPC as follows: (I) pulmonary function and exercise tests; (II) COPD composite severity index; (III) type of surgery; (IV) comorbidity index; and (V) prediction models for PPCs. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-138/rc).

Methods

Study population

Between January 2020 and June 2022, a total of 187 patients with COPD underwent preoperative risk evaluation including CPET at the Asan Medical Center (Seoul, Korea). Exclusion criteria encompassed: (I) patients who did not undergo surgery; (II) presence of significant comorbidities (e.g., heart failure and interstitial lung disease); and (III) history of lung resection.

This retrospective study finally included 83 patients who underwent surgery for lung cancer. COPD was confirmed using spirometry with a post-bronchodilator FEV₁/FVC ratio <0.7 in patients with compatible symptoms (e.g., dyspnea).

Data collection

Data including demographics, comorbidities, smoking history, symptoms, clinical tumor-node-metastasis (TNM) stage, type of lung resection surgery, and type of postoperative complications were reviewed (11). Prolonged air leak was defined as air leak for >5 days, and pneumonia was defined as clinical symptoms or signs of pneumonia and new infiltration on a chest radiograph.

Measurements

The subjective symptoms of patients were assessed by using the mMRC and CAT scores. The CAT score is an 8-item, self-administered questionnaire and we used the Korean version of the CAT score (12,13). The body mass index, airflow obstruction, dyspnea, and exercise capacity (BODE) and modified BODE index (mBODE) were calculated using body mass index, FEV₁, the distance of a 6-min walk test, VO₂ peak (presented as a percentage of the predicted value), and mMRC grade. The VO₂ peak (% of predicted value) was classified as follows: score 0 for >70% of predicted value; score 1 for 60–69% of predicted value; score 2 for 40–59% of predicted value; and score 3 for <40% of predicted value (14). Comorbidity was evaluated using the Charlson comorbidity index score. Among several prediction models for PPCs, we adopted the Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) score. All measurements were completed before the surgery.

Statistical analysis

Continuous variables were presented as mean ± standard deviation, and categorical variables were reported as counts and percentages. The Kolmogorov-Smirnov test was used to test data normality. For data with a normal distribution, the Student’s t-test was used. The Mann-Whitney U test was used for comparison of nonparametric data. Receiver operating characteristic (ROC) analysis and the Youden index were employed to set the optimal cut-off value. Variables with P<0.2 in univariable analysis were included for logistic regression analysis. Statistical significance was determined by the two-tailed P<0.05. We used IBM Statistical Package for the Social Sciences (version 24.0; SPSS Inc., Chicago, IL, USA) and R statistical package (version 4.3.0; R Foundation for Statistical Computing, Vienna, Austria) for data analysis.

Ethics statement

The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Institutional Review Board of the Asan Medical Center (approval No. 2021-0915), and the requirement for informed consent was waived because of the retrospective nature of the study.

Results

A total of 360 patients underwent CPET as part of their preoperative evaluation at the Asan Medical Center (Seoul, Korea). Among them, 187 patients were diagnosed with COPD. We excluded 106 patients based on the exclusion criteria, whereas the remaining 81 patients were included in the final analysis (Figure 1).

Figure 1 Study flowchart. CPET, cardiopulmonary exercise testing; COPD, chronic obstructive pulmonary disease; ACO, asthma-COPD overlap; PPC, postoperative pulmonary complication.

Among the 81 patients, 16 (19.8%) developed PPCs. The types of PPCs are listed in Table 1. Persistent air leakage was the most frequent complication. The baseline characteristics of patients, lung cancer stage, and type of surgery were similar between the groups with and without PPCs (Table 2).

The subjective symptoms of patients and results of assessment tools are presented in Table 3. Notably, the CAT scores exhibited differences between the two groups. The mean CAT score was significantly higher in the PPC group than in the non-PPC group (9.4±3.0 vs. 6.7±3.2; P=0.002). The results of pulmonary function test (FEV₁, D_LCO), BODE index, mBODE index, Charlson comorbidity index (CCI) score, and ARISCAT score did not differ between the two groups.

The ROC curve for the CAT score was created to identify the optimal cut-off values for predicting PPCs in patients with COPD, and 6.5 points was the optimal cut-off value for predicting PPCs and postoperative pneumonia, respectively [PPCs; area under the ROC curve: 0.757; 95% confidence interval (CI): 0.647–0.866]. Therefore, we categorized the patients into two groups based on CAT scores (<7 and ≥7); and the group with higher CAT scores (≥7) demonstrated a significant association with the development of PPCs in the logistic regression analysis. Other variables associated with PPCs are presented in Table 4. In the multivariable logistic regression analysis, we included variables with a significance level P<0.2 identified in the univariate analysis (Table 4). Among various parameters, only higher CAT scores (≥7) emerged as an independent predictor of the development of PPCs [odds ratio (OR) =9.88; 95% CI: 1.95–50.04; P=0.005]. Additionally, we analyzed the relationship between factors and the development of only pneumonia, and likewise, higher CAT scores remained the only significant predictor of postoperative pneumonia (OR =11.74; 95% CI: 1.23–1,571.28; P=0.03) (Table S1).

Discussion

In this study, we retrospectively analyzed patients with COPD who subsequently underwent lung resection surgery for lung cancer following preoperative evaluation. The primary objective of the study was to assess the value of the CAT score for predicting PPCs in patients with mild to moderate COPD. To our knowledge, this is the first study to comprehensively evaluate the potential of symptom-based scores, cardiopulmonary function tests, various composite severity indices, and PPC prediction models simultaneously for predicting PPCs. Our findings suggested that the CAT score holds a strong predictive value for the occurrence of PPCs in patients with mild to moderate COPD.

Various studies have established cut-off values for post-operative high mortality and morbidity based on FEV₁, D_LCO, SWT, and VO₂ max; therefore, these tests are commonly used before pulmonary resection. However, while the usefulness of these cut-off values in discriminating patients at very high risks is well established, their relevance in predicting PPCs in mild to moderate COPD has not been sufficiently explored. In several studies, patients with VO₂ max <10 mL/kg/min who underwent lung resection had an exceptionally high mortality rate of up to 100%, which is generally regarded as a criterion of inoperability (8,9,15). VO₂ max between 10 and 15 mL/kg/min is associated with an increased risk of PPCs, although the incidence rate varies between studies (16,17). However, the value of VO₂ max in mild to moderate COPD typically exceeds 15 mL/kg/min, which aligns with the findings of this study. No difference in VO₂ max between the PPC and non-PPC groups was observed, indicating that VO₂ max may not play a substantial role in predicting PPCs in mild to moderate COPD. In fact, one recent meta-analysis reported that VO₂ max >15 mL/kg/min was associated with improved survival but not PPCs (18). A similar pattern was observed for D_LCO. Generally, D_LCO <60% of the predicted value is associated with elevated risk of mortality and PPCs (19,20). However, the result of D_LCO in mild to moderate COPD is usually higher than 60% of the predicted value. In one study, D_LCO in early-stage COPD was associated with higher PPC rates (OR =0.97), but the relation was not clinically meaningful (21).

In contrast, the CAT score emerged as a noteworthy predictor of PPCs, which was more reliable than spirometry. After lung surgery, limitations in respiratory muscle functions, particularly the diaphragm, and reduced ventilatory response lead to reduction in vital capacity, atelectasis, and retention of secretions (22,23). Moreover, many general anaesthetic agents interfere with mucociliary clearance and increase the production of secretions (24). In mild to moderate COPD, postoperative changes in vital capacity may be similar in almost all patients, but pre-existing differences in the functions of respiratory muscle and mucus secretions may tend to intensify these processes, leading to postoperative pneumonia. However, the most frequent complication observed in this study was persistent air leakage, which is a less explainable complication for association with CAT score than pneumonia. Previous studies have reported the association between CAT score and elevated inflammatory markers such as C-reactive protein (25-28). Even in patients with preserved respiratory function, chronic bronchitis, and a smoking history, inflammatory marker levels were correlated with CAT score and exacerbations (29). This correlation suggests that a higher CAT score may also be linked to airway inflammation, potentially contributing to delayed healing and the occurrence of air leakage. The CAT score encompasses aspects related to mucus secretion, chest tightness, breathlessness, and limitation in activities, making it an effective reflection of vulnerability of the patient to postoperative complications.

The CAT score is a very simple, easily accessible, and cost-effective tool that requires little effort in assessment compared with other tests. It is a well-validated tool for COPD and measures various factors, including respiratory symptoms and functional capacity to perform daily activities, thereby estimating the quality of life of an individual. A previous study demonstrated that a high CAT score (>10) is associated with an increased risk of respiratory failure (30). Because COPD is a category of disease with various subtypes, even patients with similar lung function have varying symptoms, functional capacity, and quality of life, which may reflect the incidence of PPCs. CAT scores may better reflect those differences than other exercise tests, composite scores, or PPC prediction models. It suggests that a well-validated, simple questionnaire may be more informative than expensive and complex tests.

Absolute contraindications of lung resection surgery are well documented in previous studies. When surgery is not contraindicated, the decision to undergo surgery is made through a comprehensive evaluation. At this point, the CAT score can play a valuable role in objectively evaluating and reflecting patient symptoms and identifying those at high risk for postoperative morbidity. Uncontrolled symptoms and subsequent reductions in functional capacity may contribute to the occurrence of PPCs; therefore, patients with more severe symptoms may require more aggressive perioperative interventions to prevent PPCs. These interventions could include customized preoperative physiotherapy, including bronchial hygiene, training of respiratory muscles and exercise, and appropriate medication (e.g., mucolytics) for patients with high CAT scores (31).

This study had several limitations. First, it was a single-center retrospective study, so inherent bias may have been present owing to the nature of the study. In addition, the study only included a small number of patients, so the predictive value of tests other than CAT scores may have been underestimated. Therefore, a prospective study including a larger population would be required to further validate our study findings.

Conclusions

Our study demonstrated that the CAT score is useful in evaluating patients with COPD before lung resection surgery, as it effectively predicts the risk of developing PPCs. This suggests that patients with relatively high CAT scores may benefit from aggressive management during the perioperative period to enhance their outcomes.

Acknowledgments

Funding: None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-138/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-138/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-138/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-138/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Institutional Review Board of the Asan Medical Center (approval No. 2021-0915), and the requirement for informed consent was waived because of the retrospective nature of the study.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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