Coronary artery bypass grafting (CABG) often causes physiological changes in patients. Although functional changes, such as lung function and exercise capacity changes, are observed in patients, there are no detailed studies examining this. The aim was to compare preoperative and postoperative pulmonary function and exercise capacity in patients undergoing on-pump CABG with a multidimensional index (BODE index). Demographic and surgical characteristics of patients were recorded. Pulmonary function test, six-minute walk test (6MWT), and modified Medical Research Council (mMRC) dyspnea score were assessed and BODE index were calculated in preoperative and at six months postoperatively. A total of 75 patients were included with a mean ± standard deviation age of 59.8±10.0 years. The male to female ratio was 57/18. There was a statistically significant decrease in the forced expiratory flow at 25-75% (FEF 25-75 %) value after CABG. Other pulmonary function test values were also lower in the postoperative period compared to the preoperative period, but these changes were not significant. The mean distance achieved in the 6MWT (p=0.02) and the mMRC dyspnea score (p=0.001) were significantly better postoperatively. The BODE index, which combines these parameters, had increased in the postoperative period. Age (OR 1.09; 95% CI: 1.008-1.181) and postoperative FEF 25-75 % (OR -0.96; 95% CI: 0.938-0.988) were the independent predictors of BODE score ≥3 in multivariate analysis. Despite the decrease in pulmonary function in patients undergoing CABG, there was an improvement in exercise capacity and dyspnea score.
The effects of coronary artery bypass grafting (CABG) on pulmonary function or exercise capacity have been studied recently. However, to our knowledge, there are no studies evaluating symptoms, pulmonary functional evaluation and exercise capacity in a combined manner. BODE is a multidimensional index assessing symptoms, pulmonary functions and exercise capacity and it predicts severity of disease and prognosis, especially in chronic obstructive pulmonary disease patients. , The aim of this study was to compare preoperative and postoperative pulmonary function and exercise capacity in patients undergoing on-pump CABG with the multidimensional BODE index.
Methods
Seventy-five patients who underwent on-pump isolated CABG were included in the study. Demographic characteristics and smoking history of the patients were recorded. Smoking status was defined as non-smoker and ever smoker (current smoker or former smoker). During the operation, whether the left internal mammary artery was used, the number of conduits inserted, the total perfusion time, the cross-clamp time, the duration of placement of drainage in the thorax and mediastinum, and the length of hospitalization and stay in intensive care unit were recorded. The study was approved by Kocaeli University Non-Interventional Research Ethics Committee (2014/342). All patients were informed in detail about the study and signed informed consent was obtained from all participants.
The Modified Medical Research Council (mMRC) dyspnea scale was used for evaluation of dyspnea. Pulmonary function tests were used for functional assessment and these was performed according to the American Thoracic Society and European Respiratory Society consensus report. Forced vital capacity (FVC), forced expiratory volume in one second (FEV 1 ), FEV 1 /FVC and forced expiratory flow at 25-75% (FEF 25-75 ) values and (%) levels of the patients were recorded. A six-minute walk test (6MWT) was performed to evaluate exercise capacity, according to the American Thoracic Society guideline.
BODE index is a multidimensional evaluation system including four independent predictors which are body mass index (kg/m 2 ), the degree of airflow obstruction assessed by FEV 1 , the mMRC dyspnea score, and the exercise capacity assessed by the 6MWT ( Table 1 ). The score of the BODE index is categorized into four quartiles, as follows: quartile 1 = a score of 0-2; quartile 2 = 3-4; quartile 3 = 5-6; and quartile 4 = 7-10. An increase in the score of the BODE index is associated with poorer clinical outcomes. The pulmonary function tests, mMRC dyspnea scale and 6MWT were performed both in the preoperative period and at the sixth month of the postoperative period. The BODE index was also calculated at both time points.
| Variables | Points on bode index | |||
|---|---|---|---|---|
| 0 | 1 | 2 | 3 | |
| Forced expiratory volume in one second – FEV 1, (%) | ≥ 65 | 50-64 | 36-49 | ≤ 35 |
| 6 minute walk test – 6MWT, (meters) | ≥ 350 | 250-349 | 150-249 | ≤ 149 |
| Modified Medical Research Council – mMRC dyspnea score | 0-1 | 2 | 3 | 4 |
| Body mass index, (kg/m 2) | > 21 | ≤ 21 | ||
Statistical analyses of the study were performed using IBM SPSS for Windows version 20.0 (IBM Corporation, Armonk, NY, USA). Categorical variables were expressed as counts (percentage). Continuous variables were expressed as mean ± standard deviation (SD). Comparisons of categorical variables were performed using the chi-square test. Paired sample t-tests were used to compare preoperative and postoperative pulmonary function test parameters and 6MWT results. Preoperative and postoperative mMRC dyspnea and BODE index scores were compared by Wilcoxon Test. Binary logistic regression was performed to identify factors for multivariate analysis. A two-sided p value <0.05 was considered statistically significant.
Results
A total of 75 patients who underwent CABG with heart-lung pump were included. This consisted of 57 (76%) men and 18 (24%) women with a mean age of 59.8±10.0 years, ranging from 40 to 81 years. Among the study population 22.7% had a smoking history. The most common comorbidities were hypertension (56.7%), Diabetes Mellitus (34.7%) and Chronic Obstructive Pulmonary Disease (16%). The demographic data, surgery characteristics and clinical outcomes are shown in Table 2 .
| Characteristics | |
| Age, (mean ± SD), years | 59.8 ± 10.0 |
| Male/Female | 57/18 |
| Body mass index, (mean ± SD), kg/m 2 | 29.0 ± 5.5 |
| Number of conduits inserted | |
| 1 | 2 (2.7%) |
| 2 | 26 (34.7%) |
| 3 | 41 (54.7%) |
| 4 | 6 (8.0%) |
| Ejection fraction, (%) | 57.0 ± 9.1 |
| Duration of intubation, (mean ± SD), hours | 7.5 ± 2.2 |
| Total perfusion time, (mean ± SD), minutes | 115.8 ± 31.4 |
| Cross-clamp time, (mean ± SD), minutes | 67.9 ± 19.6 |
| Length of stay in intensive care unit, (mean ± SD), hours | 42.2 ± 16.8 |
| Duration of hospitalization, (mean ± SD), days | 6.3 ± 1.7 |
The comparison of pre- and postoperative pulmonary function test parameters and exercise capacity results are given in Table 3 . There was a statistically significant decrease in FEF 25-75 % value postoperatively, which suggests small airways impairment after CABG. There was no significant difference between groups of patients with either decreased or increased FEF 25-75 % in terms of gender, smoking history, changed number of vessels or left internal mammarian artery use. In multivariate analysis, age was the independent predictor of FEF 25-75 change (OR 1.08; CI95% 1.014-1.15; p=0.02). The other parameters included in the pulmonary function tests were also lower in the postoperative period compared to the preoperative period, but these changes were not statistically significant.
