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J Thorac Cardiovasc Surg 1999;118:1101-1109
© 1999 Mosby, Inc.
GENERAL THORACIC SURGERY |
From Divisions of Pulmonary Medicine, Cardiothoracic Surgery, and Beckman Laser Institute,a and UC Irvine Medical Center, Orange, and Chapman Lung Center,b Orange and Lakewood Regional Medical Center,c Lakewood, Calif.
Address for reprints: Matt Brenner, MD, Pulmonary and Critical Care Medicine Division, UC Irvine Medical Center, Orange, CA 92668 (E-mail: mbrenner{at}bli.uci.edu ).
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Abstract |
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Introduction |
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1,2 Therefore, we have adopted bilateral thoracoscopic staple LVRS as our standard approach to bilateral heterogeneous, severe emphysema. However, the ultimate value of bilateral versus unilateral LVRS will depend on the long-term results. Longer term survival outcomes after unilateral and bilateral LVRS procedures have not been reported. The purpose of this study was to compare 2-year mortality between bilateral and unilateral thoracoscopic LVRS in a large group of patients operated on by a single group of thoracic surgeons at one medical center.
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Methods |
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1,2
All patients who underwent unilateral or bilateral thoracoscopic staple LVRS at Chapman Medical Center from April 1994 to March 1996 were included in this evaluation. Baseline characteristics of all study patients appear in Table I. Patients underwent baseline complete pulmonary function testing, including: spirometry, gas exchange measures (room air arterial blood gas measurement, DLCO ), plethysmography, and gas dilution lung volumes. Maximum inspiratory and expiratory flow volume curves and thoracic gas volume were measured in a plethysmograph (Collins/Cybermedic Classic TCI and Body Plethysmograph; Warren E. Collins Inc, Braintree, Mass) and compared with predicted values, as previously described. 1,3 All patients underwent LVRS at Chapman Medical Center by one or both of 2 thoracic surgeons in the research group (R.J.M., R.J.F.). No procedures were performed at any other center in this protocol.
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Contraindications to surgery included current cigarette smoking, age greater than 80 years, severe cardiac disease (congestive heart failure, significant coronary or valvular disease), history of cancer within the last 5 years, ventilator dependency, or prior thoracic surgery. Relative contraindications included age older than 75 years, severe anxiety, severe depression, or CO2 retention with resting PaCO 2 higher than 55 mm Hg. 1,3
To be accepted for the procedure, the patient had to have a pattern of emphysema, seen on computed tomography (CT), that was severe and heterogeneous. Radionuclide lung perfusion scans were also used to confirm the heterogeneous pattern of emphysema. 1,3
Thoracoscopic LVRS operative methods
Operative procedures for thoracoscopic staple LVRS have been described previously. 1,2 All patients underwent video-assisted thoracic surgery while under paralyzed (pipecuronium) general anesthesia (isoflurane), with use of a left-sided double-lumen tube (Mallincrodt Anesthesia, St Louis, Mo).
Procedures were performed by one surgical group (R.J.M., R.J.F., M.B.) with the patient in the lateral decubitus position. The trocar and thoracoscope were placed through the 10th intercostal space in the posterior axillary line. Three additional 1- to 2-cm incisions were made for standard instruments. Patients undergoing bilateral thoracoscopic procedures were turned to the contralateral decubitus position for separate sterile preparation and draping after the procedure on the initial side was completed.
Preoperative lung CT scans and ventilation-perfusion (·V/Q· ) scans were used to identify areas of dysfunctional or degenerated lung targeted for resection with the staples.1,2 Ring forceps were used to manipulate the lung into a 60-mm endoscopic stapler (ELC 60; Ethicon, Cincinnati, Ohio) with bovine pericardium (Peristrips; Biovascular, Saint Paul, Minn) or bovine collagen matrix (Instat; Johnson and Johnson, New Brunswick, NJ) used to buttress the staples. The staples were fired an average of 15 times for bilateral operations. Typically, approximately half of the upper lobe was resected in patients with upper lobe disease.
Survival
Survival status was assessed for all patients by contacting them directly or their referring physicians between March and June 1998. The latest date of known survival was recorded, and the date and cause of death (if known) were recorded for patients who had died. Six patients had undergone a second LVRS procedure. These patients’ records were coded for their first surgical procedure with all available follow-up in accordance with "intent-to-treat" methods. Patients with survival beyond Feb 28, 1998, were censored as of Feb 28, 1998, for purposes of survival analysis.
Response assessment
To be included in the follow-up evaluation analyses of pulmonary function in this study, patients were required to have follow-up pulmonary function testing at 2 years ± 6 months after surgery. To be included in the follow-up evaluation analyses of mortality in this study, patients were required to have had their surgical procedure between the period of April 1994 and March 1996. All study patients had known mortality or survival information.
Statistical analysis
Baseline characteristics for patients undergoing unilateral or bilateral surgery are described in terms of means and standard error of the mean. Comparison of differences between patients before and after surgery is determined by 2-tailed paired t tests. Differences between surgery groups at baseline are tested by 2-tailed t tests for continuous variables or chi-square tests for categorical variables. Overall survival is calculated by using the Kaplan-Meier survival analysis. Differences between survival curves for unilateral and bilateral surgery are tested using the log-rank test. To examine the influence of potential confounders and control for baseline differences in pulmonary function, we used stratified Kaplan-Meier methods. Patients were stratified into 2 groups by baseline characteristics, using the cut points forced expiratory volume in 1 second (FEV1; 0.50 L/s), PaO 2 (55 mm Hg), age (70 years), forced vital capacity (FVC; 1.5 L), total lung capacity (TLC; 8.5 L), residual volume (RV; 5.5 L), and surgery date (eg, May 1, 1995). Cut points for FEV1, PaO 2, and age were chosen according to an earlier published definition of high-risk subgroups. 4 Cut points for FVC, TLC, and RV were arbitrarily defined as the limit of the highest risk quartile after finding that the cutoffs for FEV1 and PaO 2 approximated the lower limits of the highest risk quartile. Differences between the bilateral and unilateral surgery groups after stratification was taken into account were tested with the log-rank test.
In addition, we used Cox proportional hazards methods to test the significance of differences between surgery groups after simultaneously adjusting for baseline differences between patients. To adjust for patient heterogeneity and baseline differences between the surgical groups, we calculated a propensity score to be included as a covariant in the Cox regression analysis. 5 The propensity score, calculated by logistic regression with "surgery type" used as the dependent variable, represents the likelihood for a patient with specified baseline values to have unilateral, versus bilateral, surgery. Independent variables included in the estimation of propensity scores are age, sex, FEV1, PaO 2, FVC, TLC, RV, and surgery date. For 33 patients with missing data, data were imputed by regressing that variable against all variables with acceptable values for that individual in a stepwise procedure. Three patients had insufficient data for imputation. Covariables included in the Cox regression analysis are propensity score, age, sex, FEV1, PaO 2, FVC, TLC, RV, and surgery date. Analyses were conducted by using the Systat 7.0 for Windows and BMDP 7.0 statistical software packages (SPSS Inc, Chicago, Ill).
Rehabilitation
Patients did not receive preoperative rehabilitation at Chapman Medical Center before undergoing LVRS. All patients underwent a regimen of pulmonary rehabilitation at Chapman Medical Center immediately following hospital discharge after surgery. The rehabilitation consists of a 10-day outpatient regimen involving a multidisciplinary approach with nursing, respiratory, dietary, nutritional, psychosocial, occupational, and physical therapy. Patient education, physical exercise (walking, flexibility, and strengthening), self-monitoring, breathing retraining, and bronchial hygiene instruction are included.
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Results |
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Unilateral thoracoscopic staple LVRS–treated patients
Overall survival at 1 and 2 years was 81.1% (95% CI 73.6%-88.6%) and 72.6% (95% CI 64.2%-81.2%), respectively, after unilateral thoracoscopic LVRS (Fig 1, Table II).
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Average follow-up time was 28.5 months (range, 6 days to 46.6 months) for the bilateral LVRS group and 29.3 months (range, 6 days to 45.0 months) for the unilateral patients. During this period, 27% (29/106) of unilaterally treated study patients died of respiratory failure (Table III). In comparison, 6% (10/154) of bilaterally treated patients died of respiratory failure.
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6 (age > 70 years, PaO 2 
55 mm Hg, FEV1 0.5) were examined for their effects on outcome in unilateral, compared with bilateral, LVRS patients.
Thirty-two percent (30/94) of patients who underwent unilateral LVRS had baseline hypoxemia defined as PaO 2 55 mm Hg, compared with 21% (32/149) of patients who underwent bilateral LVRS. When stratified by baseline PaO 2, survival was better for bilateral LVRS patients (log-rank test, P = .02; Fig 2, Tables IV and V).
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8.5 L), bilateral surgery demonstrated better survival than unilateral LVRS (P = .01). When patients were stratified by baseline RV (>5.5 L, 5.5 L), patients who received bilateral LVRS again had better survival than patients who received unilateral surgery (P = .005). For the date of surgery (after May 1, 1995), stratified Kaplan-Meier analysis showed a significant advantage for bilateral surgery (P = .002). In an attempt to simultaneously control for patient heterogeneity and any baseline differences between the two surgery groups, we analyzed data using the Cox regression analysis. After adjusting for all covariables (propensity score, age, gender, FEV1, PaO 2, FVC, TLC, RV, and surgery date) in a proportional hazards model, the hazard ratio for unilateral LVRS compared with bilateral surgery was 2.00 (P = .05, 95% CI 1.02-3.92). No significant interactions existed between surgery type and the other risk factors in the model.
Baseline characteristics and lung function studies
Baseline characteristics revealed statistically significant differences between patients who underwent unilateral and patients who underwent bilateral procedures in PaO 2 (Table I
). In general, patients who underwent unilateral procedures did not have more severe disease than those who underwent bilateral procedures.
Lung function
Follow-up pulmonary function results are available on 108 patients (40% of total population) at 2 years ± 6 months after the date of the operation. Sixty-nine of these patients had bilateral thoracoscopic staple LVRS, whereas 39 had unilateral thoracoscopic staple LVRS.
Two years after unilateral LVRS, mean improvement in FEV1 was 77 mL, while mean improvement in FVC was 301 mL above preoperative levels. Mean FEV1 was 731 mL preoperatively and rose to 808 mL 2 years after the operation. Mean FVC was 2.232 L preoperatively and rose to 2.533 L 2 years after the operation. Average follow-up time after unilateral LVRS until pulmonary function testing was 24.6 months.
Two years after bilateral LVRS, mean improvement in FEV1 was 274 mL, while mean improvement in FVC was 711 mL above preoperative levels. Mean FEV1 was 666 mL preoperatively and rose to 940 mL 2 years after the operation. Mean FVC was 2.040 L preoperatively and rose to 2.751 L 2 years after the operation. Average follow-up time after bilateral LVRS until pulmonary function testing was 23.2 months.
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Discussion |
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1,3,4,7-12 Bilateral staple LVRS appears superior to unilateral staple LVRS in achieving these benefits in short-term follow-up, with similar operative morbidity and mortality. 7-11,13-20 Longer term outcome information is needed before definitive conclusions can be drawn regarding the overall value of unilateral versus bilateral LVRS in severe emphysema patients.
This study shows significant and substantially greater survival at an average of more than 2 years’ follow-up of patients who underwent bilateral, compared with unilateral, LVRS. Two-year mortality was 13.6% for bilateral LVRS patients and 27.4% for the unilaterally treated patients (P = .001). There are a number of possible reasons for this apparently greater survival after bilateral procedures. Pulmonary function improvements are greater after bilateral LVRS, compared with unilateral procedures. 1,7-10,17 The effects of greater improvements in oxygenation, lung, diaphragmatic, chest wall, dynamic hyperinflation, and respiratory muscle function, 2,11,21-25 or all of the above, may contribute to superior survival after bilateral LVRS (Table II).
FEV1 has been shown to correlate with survival in patients with emphysema in previous studies. 21,22 Patients undergoing bilateral staple LVRS demonstrate superior sustained improvements in FEV1 and FVC at 2-year follow-up that may explain the improved overall survival. In previous analyses of bilateral LVRS patients, we found that patients with greatest short-term improvement in pulmonary function tests have better long-term survival. 6 In the current study, FEV1 for these patients was 274 mL above baseline, compared with only 77 mL above baseline in the unilateral LVRS patients 2 years after bilateral LVRS. These findings are limited by the fact that less than half of the study population had complete follow-up spirometry at 2 years. Therefore, these values may not be truly representative of the total study population. Nonetheless, the differences in overall survival between unilateral and bilateral LVRS patients are seen both in the short-term and the long-term. This may reflect improved ability to survive the acute morbidity of surgery, as well as the longer term pulmonary function benefits of more extensive resection.
The patients who underwent unilateral procedures were not randomized. Therefore, it is a theoretical possibility that preoperative patient selection characteristics could have favored patients undergoing bilateral surgery and thus explain superior long-term survival after bilateral LVRS. Nevertheless, we do not think procedure choice was based on the preoperative level of overall comorbidity. Further, the majority of the unilateral surgeries were performed early in our experience with LVRS. Unilateral LVRS were performed most commonly later in our experience for patients with clear unilateral disease. When patients were stratified by covariables known to be associated with survival and data were analyzed by stratified Kaplan-Meier analysis and log-rank tests, differences between bilateral and unilateral LVRS remained significant. Also, the consistent pattern shown in the univariate analyses strongly supports the survival advantage associated with bilateral surgery in this group of patients.
Overall 2-year survival in bilateral LVRS patients in this series (86%) is similar, but not identical to 2-year survival we recently reported in patients who underwent bilateral staple LVRS at this center (81%). 6 The slight differences in reported survival arise from exclusion in the current study of patients who underwent median sternotomy and exclusion of patients who underwent surgery less than 2 years ago.
Overall longer term survival has not been previously reported comparing unilateral with bilateral LVRS procedures. Short-term lung function response results favor bilateral procedures but do not necessarily predict long-term response. Such information is important since the upcoming NIH-sponsored National Emphysema Treatment Trial examines only bilateral procedures, assuming they are superior to unilateral procedures overall. The current study suggests that long-term survival outcome also favors bilateral LVRS.
Thus far, there has been only 1 study to demonstrate overall survival benefit from LVRS compared with conventional medical management. 26 The current study does not have a medical control arm for direct comparison of LVRS survival effects. However, we believe this study provides further, albeit indirect, evidence to suggest that bilateral LVRS may improve overall survival by the following reasoning. If findings from this study are confirmed in other centers, there are at least 2 possible interpretations why bilateral LVRS may be associated with significantly improved survival, compared with unilateral procedures: (1) bilateral procedures improve overall survival, or (2) both procedures reduce survival, but bilateral procedures cause less survival deterioration than unilateral procedures. While the latter explanation is possible, it is unlikely that more extensive bilateral procedures would cause less damage than more limited unilateral procedures if both are detrimental. Thus, the most likely explanation for the significantly greater bilateral LVRS outcome is due to overall improvement in survival from bilateral LVRS. Thus, while these data are suggestive of overall survival benefits after bilateral LVRS, a controlled study would be needed for definitive proof.
In summary, bilateral staple LVRS appears to be superior to unilateral staple LVRS for the treatment of severe heterogeneous emphysema and can be accomplished safely by using a video-assisted approach. While prior studies have documented the superior acute palliative effects of bilateral staple LVRS over unilateral staple, the present study documents superior survival 2 years after bilateral staple LVRS.
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Footnotes |
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Supported in part by DOE Grant DE-F603-91ER61227, ALA Grant CI-030-N, CTRDRP Grant 6RT-0158, ACS Faculty Grant.
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