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Ann Thorac Surg 2003;76:356-361
© 2003 The Society of Thoracic Surgeons
a Department of Thoracic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan
Accepted for publication March 4, 2003.
* Address reprint requests to Dr Fujisawa, Department of Thoracic Surgery, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan
e-mail: fujisawa{at}med.m.chiba-u.ac.jp
| Abstract |
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METHODS: We conducted a retrospective chart review of 521 patients who had undergone lobectomy for lung cancer at Chiba University Hospital between 1990 and 2000. Forty-eight patients were categorized as COPD, defined as percentage of predicted forced expiratory volume at 1 second (FEV1) less than or equal to 70% and percentage of FEV1 to forced vital capacity less than or equal to 70%. The remaining 473 patients were categorized as non-COPD.
RESULTS: Although all preoperative pulmonary function test data and arterial oxygen tension were significantly lower in the COPD group, postoperative arterial oxygen tension and FEV1 were equivalent between the two groups, and the ratio of actual postoperative to predicted postoperative FEV1 was significantly better in the COPD group (p < 0.001). With multivariable analysis, COPD and pulmonary resection of the lower portion of the lung (lower or middle-lower lobectomies) were identified as independent factors for the minimal deterioration of FEV1. Actual postoperative FEV1 was 15% lower and higher than predicted, respectively, in the non-COPD patients with upper portion lobectomy and the COPD patients with lower portion lobectomy. Finally, we created a new equation for predicting postoperative FEV1, and it produced a higher coefficient of determination (R2) than the conventional one.
CONCLUSIONS: The postoperative ventilatory function in patients with COPD who had lower or middle-lower lobectomies was better preserved than predicted.
| Introduction |
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To evaluate the functional resectability for lung cancer, the preoperative pulmonary function test (PFT) is still the gold standard, and ppoFEV1 is the most reliable predictor for mortality and morbidity [2, 9]. Although several approaches, such as inhalation perfusion (single-photon emission computed tomography) imaging [10], perfusion lung scintigraphy [11], and quantitative computed tomography [12] have been proposed for predicting precise postoperative FEV1, none of these methods has been proven to be more accurate than the simple calculation based on the number of the bronchopulmonary segments removed. However, recent studies have shown that underestimation of the actual postoperative FEV1 may occur due to heterogeneous distribution of ventilation and perfusion [13].
The purpose of this study was to evaluate the influence of COPD on the change in pulmonary function after lobectomy in lung cancer patients and to elucidate the characteristics of patients with less diminished postoperative pulmonary function in order to establish a more accurate formula for predicting postoperative FEV1.
| Patients and methods |
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Airway obstruction was defined as percentage of predicted forced expiratory volume in 1 second (percent predicted FEV1) at or below 70% and FEV1:FVC at or below 70% [7, 14]. FEV1 and FEV1:FVC were independent predictors of all cause or respiratory disease mortality [15]. These two variables were used to grade the severity of obstructive abnormalities. In the American Thoracic Society statement [16], when FEV1:FVC is below the normal range (less than 70% to 80% of predicted), percent predicted FEV1 less than 70% was recognized as moderate COPD and less than 50% as severe. Therefore, the criterion of this study was defined as moderate. No bronchodilator was used at PFT. Forty-eight patients fulfilled this criterion (COPD group), and the other 473 were categorized as non-COPD. Only 7 patients had less than 50% of preoperative predicted FEV1, and 1 patient had critically severe emphysema with 0.76 L (27.6% of predicted) of preoperative FEV1. Incentive spirometry was used routinely for enhancing lung expansion 2 weeks before and after the operation. Preoperative pulmonary rehabilitation for COPD patients was done from the time of admission to operation (approximately 2 weeks). If PFT data fulfilled the COPD criterion, preoperative PFT was repeated after the respiratory rehabilitation for the final classification.
We estimated ppoFEV1 by using the following equation: ppoFEV1 = preoperative FEV1 x (1 S x 0.0526), where S = number of resected bronchopulmonary segments [17]. After actual postoperative FEV1 (apoFEV1) was obtained, the ratio of apoFEV1 to ppoFEV1 (apo/ppo FEV1) was calculated. Then, the minimal deterioration of postoperative FEV1 was determined when apo/ppo FEV1 was 1.15 or more, which was the highest 10% in this study population. This cut-off point was determined based on the distribution of apo/ppo FEV1. We created a histogram where the apo/ppo FEV1 was divided every 0.05. The parametric method was not appropriate for analysis because the distribution had two peaks (n = 69 at 1.00 to 1.05 and n = 21 at 1.15 to 1.20). Therefore, the cut-off point was set to the trough (apo/ppo FEV1 = 1.15) between the two peaks.
The clinical record of each patient was reviewed for the following information: age, gender, body mass index, smoking history, concomitant diseases, and postoperative complications. Positive smoking history included any former smokers as well as current smokers. Descriptions of operations were studied for method of thoracotomy and portion of lobectomy. We divided the portion of lobectomy into two groups, upper portion (upper, middle or upper-middle lobectomies) and lower portion (lower or middle-lower lobectomies). Pathologic staging was determined according to the TNM (tumor, node, and metastasis) classification by Mountain [18].
To evaluate the radiologic severity of emphysema, chest conventional or high-resolution computed tomography was reviewed utilizing the semiquantitative method reported by Goddard and colleagues [19]. A total of three slices were obtained from the lung apex to the lung base at the following levels: upper margin of the aortic arch, origin of the middle lobe bronchus, and right lower pulmonary vein. Right and left lungs were evaluated separately. Then each of the six views was classified into five grades as follows: grade 0 = no emphysema, 1 = emphysematous lesions less than 25%, 2 = emphysematous lesions between 25% and 50%, 3 = emphysematous lesions between 51% and 75%, and 4 = emphysematous lesions over 75%. Areas of low attenuation, indicating less than -950 HU (the lowest level of the mean computed tomographic value of normal lung), and vascular disruption were considered to be suggestive of emphysema [19]. The evaluation was performed by three thoracic specialists independently in a blinded fashion, and the final score was calculated as the mean of scores assigned by the three readers.
Finally, we classified all patients into four subgroups according to the results of multivariable analysis, created the new equation for predicted postoperative FEV1, and validated the usefulness of this formula in 142 lung cancer patients who matched the criteria of this study and had lobectomy at our hospital between April 2000 and March 2002.
Statistical analysis
Data were analyzed using the Stat View Version 5.0 (Statistical Analysis Systems; Cary, NC, USA) by a statistician. To compare the differences between the COPD and non-COPD groups, a Mann-Whitney U test was utilized to analyze continuous variables, and the
2 test or Fisher exact test to analyze for categorical variables. The correlation between ppoFEV1 and apoFEV1 was calculated by simple linear regression analysis. The Tukey-Kramer multiple comparison was applied for comparing variables among four subgroups. All preoperative and intraoperative variables including gender, age, body mass index, pathologic type and stage, existence of COPD, portion of lobectomy, type of thoracotomy, operative time, and blood loss were entered into a logistic regression model to identify variables that were independently predictive of less deteriorated postoperative FEV1 (apo/ppo FEV1
1.15). A p value less than 0.05 was considered statistically significant.
| Results |
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| Comment |
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In this study, we clarified that in COPD patients, defined by pulmonary function tests, arterial blood gas data were undiminished and pulmonary function was less diminished when compared to the data from patients with normal airflow obstruction. In particular, FEV1:FVC improved after lobectomy in COPD patients. This phenomenon occurred not only in patients with heterogeneous emphysema but also in those with homogeneous emphysema confirmed by chest computed tomographic evaluation. Furthermore, by multivariable analysis, lobectomy of lower portion (lower lobectomy or middle-lower lobectomies) was an independent factor for inducing the minimal deterioration of postoperative FEV1. Finally, we established a modified formula for predicting postoperative FEV1 based on the bronchopulmonary segments according to the existence of COPD and the portion of lobectomy.
The effects of lung volume reduction are thought to be related to restoration of the elastic recoil of pulmonary parenchyma and improvement of thoracic motion [21, 22]. However, the mechanism of change of pulmonary function in the COPD patients of this study seemed to be different. First, the subjects of this study were not patients with severe emphysema who needed volume reduction operations. Second, both FVC and FEV1 did not increase in the COPD patients. This may be due to removal of functioning lung tissues. Third, lobectomy of the lower portion resulted in better residual lung function compared with upper portion lobectomy. In general, emphysema is more predominant in the upper lobe than in the lower lobe; therefore, the target of lung volume reduction is frequently the apex of the upper lobe. No patient had alpha 1 anti-trypsin deficiency, and there was no emphysema predominant in the lower lobe. We sometimes find occasional anatomic repositioning after upper lobectomy, which causes narrowing of the orifice of lower or middle lobe bronchus [23]. Conversely, lower lobectomy usually has no effect on the remaining upper and middle bronchus. These anatomic differences may have influenced the synchronization of lung and chest wall motion.
After lobectomy, residual lungs overinflate, the diaphragm elevates, the mediastinum shifts to the operative side, and the intercostal space is reduced in order to fill the space of the resected lung. We speculate that the movement and elevation of the diaphragm may be different between postlower lobectomy and postupper lobectomy [24]. To answer this question, we are now conducting a prospective study to determine the cause of good postoperative FEV1 after lobectomy of the lower portion in COPD patients.
This retrospective study has certain limitations. First, preoperative optimization of respiratory reserve in the COPD patients on medications (including antibiotics, bronchodilators, and steroids) and physical rehabilitation are all confounding variables. Because the study was not controlled, these factors were not incorporated into our statistical analysis. Second, the recovery of ventilatory function takes at least 3 to 6 months [25, 26]. In this study, postoperative PFT was measured 1 month after operation, which is earlier than that of other studies [3, 4]. The postoperative lung function might not have been fully recovered at this point. The main cause of loss of forced respiratory maneuvers is restricted thoracic wall motion influenced by wound pain [27]. The severity of postoperative pain depends on the method of thoracotomy and affects pulmonary gas exchange immediately after thoracic operation [28]. However, we found that the method of thoracotomy was not an independent factor influencing the outcome of less diminished FEV1. We speculate that wound pain might not have strongly affected the PFT data in this study. Giordano and associates [11] reported that perfusion lung scintigraphy could predict postlobectomy residual lung function 1 month after operation. Because pulmonary function recovers in a time-dependent manner [25], the postoperative PFT data 1 month after operation may be consistent with the long-term pulmonary function.
Finally, we established a modified equation for predicting postoperative FEV1. If a patient has marginal pulmonary function, such as 800 mL of ppoFEV1, and lower lobectomy is planned, the patients modified ppoFEV1 would become 920 mL, which is acceptable for operation. This new equation has a potency of expanding the functional indication of standard operation for lung cancer patients with COPD.
In conclusion, although COPD patients have a higher risk of postoperative complications, the preservation of ventilatory function may be better than predicted. In particular, lobectomy of the lower portion induced minimal deterioration of postoperative FEV1. Therefore, we propose a new equation for predicting individual postoperative FEV1 according to the patients pulmonary function and the portion of the lung lobe resected.
| Acknowledgments |
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| References |
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