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* From the Division of Cardiothoracic Surgery and Interventional Pulmonology (Drs. Ernst, Majid, Feller-Kopman, Guerrero, O’Donnell, DeCamp, Gangadharan, and Ashiku), Department of Radiology (Dr. Boiselle), and Department of Anesthesia and Critical Care (Dr. Loring), Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA; and Division of Pulmonary and Interdisciplinary Endoscopy (Dr. Herth), Thoraxklinik, Heidelberg, Germany.
Correspondence to: Armin Ernst, MD, FCCP, Chief, Interventional Pulmonology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Ave, Boston, MA 02215; e-mail: aernst{at}bidmc.harvard.edu
Abstract
Rationale: It is postulated that in patients with severe tracheobronchomalacia (TBM), airway stabilization with stents may relieve symptoms.
Objectives: To evaluate the effect of silicone stents (tracheal, mainstem bronchus, or both) on symptoms, quality of life, lung function, and exercise capacity in these patients.
Methods: A prospective observational study in which baseline measurements were compared to those obtained 10 to 14 days after stent placement.
Measurements and main results: Of 75 referred patients, 58 had severe disease and underwent therapeutic rigid bronchoscopy with stent placement. Mean age was 69 years (range, 39 to 91 years), 34 were men, 33 had COPD, and 13 had asthma. Almost all patients (n = 57) had dyspnea as a sole symptom or in combination with cough and recurrent infections; four patients required mechanical ventilation for respiratory failure. In 45 of 58 patients, there was reported symptomatic improvement; quality of life scores improved in 19 of 27 patients (p = 0.002); dyspnea scores improved in 22 of 24 patients (p = 0.001); functional status scores improved in 18 of 26 patients (p = 0.002); and mean exercise capacity improved from baseline, although not significantly. The 49 complications included mainly 21 partial stent obstructions, 14 infections, and 10 stent migrations. Most patients with concomitant COPD also improved on most measures.
Conclusions: In the short term, airway stabilization with silicone stents in patients with severe TBM can improve respiratory symptoms, quality of life, and functional status. Coexisting COPD is not an absolute contraindication to a stenting trial in this population. Stenting is associated with a high number of short-term and long-term but generally reversible complications.
Key Words: airway stabilization • bronchoscopy • COPD • stent placement • tracheobronchomalacia
Tracheobronchomalacia (TBM) is an abnormal collapse of the tracheal and bronchial walls. It is characterized by flaccidity of the supporting tracheal and bronchial structures and a significant reduction of airway diameter on expiration seen in the trachea and/or in the mainstem bronchi.12
The prevalence of TBM in adults is unknown. The incidence may be as high as 23% among patients with COPD undergoing bronchoscopy,3 and may represent 1% of all patients undergoing bronchoscopy.4 One study5 found TBM to be the cause of chronic cough in 14% of nonsmoking patients.
The cause of TBM is often unknown, but it is frequently seen in patients with common respiratory conditions such as chronic bronchitis and emphysema.6 This pathologic narrowing can produce dynamic outflow obstruction with symptoms such as dyspnea, orthopnea, cough, wheezing, and the inability to clear secretions, predisposing the patient to recurrent infections and wheezing. Some patients may present with stridor, respiratory failure leading to intubation, or immediate respiratory failure after extubation.78
The severity of TBM is conventionally graded by the degree of airway collapse during forced expiration (intrathoracic malacia) or inspiration (extrathoracic malacia). Based on expert opinion, collapse < 50% is within normal limits, while 50 to 75% is mild, 75 to 90% is moderate, and 91 to 100% (approximation of posterior membrane to the anterior luminal surface) is severe malacia.
Tracheomalacia has been recognized with increased frequency due to both improved clinical awareness and diagnostic imaging. While most experts still agree that functional bronchoscopy is the "gold standard" for diagnosis, there are no standardized protocols guiding respiratory maneuvers and airway measurements during these procedures. In the past few years, dynamic airway CT has proved to be highly sensitive for the diagnosis of malacia.9
Current treatments include techniques that splint the central airways, such as continuous positive airway pressure,10 silicone airway stents,11 and surgical tracheobronchoplasty.12 In patients with severe, symptomatic TBM, stenting may provide symptomatic relief through airway stabilization. Unfortunately, most reports of this approach are anecdotal, and no controlled study has assessed the efficacy of airway stents for treating tracheomalacia.1314 This prospective study was designed to evaluate the efficacy of silicone airway stents in improving symptoms, quality of life, lung function, and exercise capacity in patients with severe TBM.
Materials and Methods
The institutional review board of Beth Israel Deaconess Medical Center approved the protocol and patients gave written informed consent. We conducted a prospective, observational study from January 2002 to September 2006 in all patients referred to our Complex Airway Center for the evaluation of respiratory symptoms presumed to be caused by TBM. All patients who underwent central airway stenting (tracheal, mainstem bronchus, or both) for the treatment of severe TBM (n = 58) were considered for evaluation.
Severe TBM was defined by near-total or total airway collapse (with approximation of posterior and anterior luminal surfaces) observed during bronchoscopy. Patients were receiving maximal medical therapy for comorbidities such as obstructive airway disease. Those treatments included inhaled short-acting bronchodilators (ß-adrenergic and anticholinergic), long-acting bronchodilators, inhaled corticosteroids, and oral corticosteroids.
Age, sex, comorbidities, and respiratory symptoms were recorded at baseline. All patients underwent dynamic airway CT and functional bronchoscopic assessment. In addition, unselected subsets of patients underwent spirometry testing, 6-min walk test (6MWT), and completed standardized questionnaires including the modified St. George respiratory questionnaire (SGRQ),15 baseline dyspnea index (BDI)/transitional dyspnea index (TDI),16 American Thoracic Society (ATS) dyspnea score, and Karnofsky performance scale (KPS).17
Silicone stents were placed in all patients to stabilize the airway. Tracheal, bronchial, and bifurcated silicone stents (Dumon tracheal stent size 16, Dumon bronchial stent size 14, and Dumon bifurcated (Y-stent) sizes 14–18; Novatech-Boston Medical Products; Westborough, MA). The degree and location of malacia, the type and location of stent placement, and any complications during stent insertion were also recorded.
At a scheduled follow-up visit 10 to 14 days after the procedure, patients were asked whether symptoms had improved and baseline measurements were repeated. The 2-week window was chosen to minimize confounding factors, such as possible stent complications and any potential long-term impacts of physical conditioning between stent placement and follow-up measurements. Patients were followed up after that for any stent-related complications.
Functional Bronchoscopic Assessments
All bronchoscopies were performed with topical anesthesia and light sedation, which allowed patients to follow commands. The bronchoscope was introduced into the trachea and advanced to approximately 5 cm above the carina. At that point, the patient was instructed to perform a forced expiratory maneuver. This procedure was then repeated at the entrances of the right and left main bronchi. All bronchoscopies were video recorded and reviewed after the procedure to assess the degree of airway collapse before stent placement (Fig 1
), as described in detail.18
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All patients underwent imaging using a CT central airway protocol,9 which includes end-inspiratory and dynamic expiratory imaging. Before helical scanning, initial scout topographic images were obtained to determine the area of coverage, which included the trachea and central bronchi, and that corresponded to a length of approximately 10 to 12 cm. Helical scanning was performed in the craniocaudal dimension during both end-inspiratory and dynamic expiratory phases.
To calculate the percentage of luminal collapse, the estimated dynamic expiratory cross-sectional area was subtracted from the end-inspiratory cross-sectional area, divided by the end-inspiratory cross-sectional area, and then multiplied by 100. Malacia was determined to be present if the percentage of luminal collapse during dynamic expiration was 
50%. The distribution of malacia in the trachea and bronchi was also recorded (Fig 2
).
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The 6MWT, an objective evaluation of functional exercise capacity, was performed according to ATS guidelines.20 An improvement > 230 feet was considered clinically important.21
We used the BDI and the TDI as objective measures of dyspnea. The BDI represents the severity of dyspnea at baseline and is based on three components: functional impairment, magnitude of the task, and the magnitude of the effort. Each component is scored 0 to 4, so the summed scores range from 0 (severe) to 12 (normal). The TDI indicates the change from baseline. The TDI uses the same components as the BDI, but each component is graded from – 3 (major deterioration) to + 3 (major improvement). The summed scores range from – 9 (major deterioration) to + 9 (major improvement).16
The ATS dyspnea score, although less well studied, is easy to use and also provides an objective measurement for dyspnea in this population. Scores range from 0 (no dyspnea) to 4 (severe dyspnea).
A modified SGRQ15 was used to measure the impact of respiratory symptoms on overall health, daily life, and perceived well-being. The questionnaire has been widely used in patients with COPD and asthma. In our study, many patients had COPD, asthma, or both. The questionnaire has three dimensions (symptoms, activities, and impacts). Each dimension describes the respiratory problems encountered by the patient in the preceding 2 weeks (instead of 4 weeks) and is scored from 0 to 100, with higher scores indicating poorer health. Empirical data and interviews with patients indicate that a mean change score of 4 U is associated with a slightly efficacious treatment, 8 U with a moderately efficacious treatment, and 12 U with a highly efficacious treatment.1522
The KPS, which classifies patients by functional impairment, has been used to compare the effectiveness of different therapies and to assess the prognosis of individual oncology, geriatric, and stroke patients.2324 Scores range from 0 to 100. The lower the score, the greater the impairment and the worse the prognosis.25
Airway Stenting
All airway stents were placed in the operating room with the patient under general IV anesthesia. After anesthesia was induced, a rigid bronchoscope (Bryan-Dumon Series II; Bryan Corporation; Woburn, MA) was introduced, and respiration was maintained through jet ventilation.
After assessing the airways and remeasuring the lengths of the left and right mainstem bronchi, we placed either a Y-shaped stent or multiple stents. Stents were placed in the standard fashion, and a good fit was confirmed visually. All stents were made from silicone to allow easy removal if necessary (Fig 3 ).
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was set at 0.05, and all tests were two-tailed. Statistical software (SAS, version 9.1.3 for Windows; SAS Institute; Cary, NC) was used for all analyses. Results
Of 75 patients referred for assessment of TBM during the study period, 58 had severe TBM and were able to undergo therapeutic rigid bronchoscopy under general anesthesia. The patients included in this study were on average 69 years old (range, 39 to 91 years), and 34 patients (59%) were men. Among all patients, 33 patients had COPD (57%; median FEV1, 1.07 L); 13 patients (22%) had asthma; 16 patients (28%) had obstructive sleep apnea; 16 patients (28%) had gastroesophageal reflux disease; and 3 patients (5%) had Mounier Kuhn syndrome, with some patients suffering from more than one (Fig 4 , top, A).
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Most patients (n = 46, or 80%) had diffuse TBM and were treated with either a combination of a silicone tracheal and left main stent (n = 19) or a Y-stent (n = 27). Six patients each were treated only with bronchial or only with tracheal stents.
The following numbers of subjects had baseline and follow-up data collected for each outcome: SGRQ, n = 38 and n = 27; BDI/TDI, n = 41 and n = 24; ATS dyspnea score, n = 41 and n = 29; KPS, n = 41 and n = 26; 6MWT, n = 36 and n = 17; and FEV1, n = 42 and n = 10, respectively. For all measures, median baseline values of those patients in whom follow-up was also obtained were comparable to baseline median values for all patients.
SGRQ, BDI/TDI, ATS, and KPS scores improved among both the complete sample with baseline and follow-up measures and the subset of patients with COPD. There were no significant changes in 6MWT results or FEV1 (Table 1 ).
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Complications occurred usually within the first 3 months (median, 26 days; range, 3 to 865 days). Of these complications, 44 complications (90%) were related to the stent, 5 to bronchoscopy, and none to anesthesia. Complications included stent obstruction secondary to mucous plugging (n = 21), infection (n = 14), stent migration (n = 10), severe cough (n = 3), subglottic edema (n = 3), and stent breakage (n = 1). All complications were treated in standard fashion with mucolytics, cough suppressants, and stent removal or replacement if necessary (Fig 6 ). Stenting improved the median scores of all clinical end points, and most patients reported improvement (Table 1; Fig 7, 8 ).
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There is a need for a higher clinical suspicion and a standardized approach to objectively evaluate for TBM in the patient with dyspnea refractory to traditional therapies. Therapeutic airway stenting is often considered, but evidence for the efficacy of this approach has not been adequately characterized. In this largest prospective study to date, we found that stenting produced statistically significant and clinically important improvement in dyspnea, health-related quality of life, and functional status in a selected patient population with severe TBM. As there were no concurrent changes in medication or physical rehabilitation, we attribute these positive outcomes to the impact of central airway stabilization.
Importantly, 33 of our 58 patients (57%) had COPD. In these patients, TBM is often believed to be an extension of peripheral airway obstruction. In fact, it has been suggested in retrospective, uncontrolled studies26 that TBM in these patients may not be responsive to aggressive treatment. Our study suggests that COPD patients may benefit from central airway stabilization in severe TBM. Irrespective of any direct impact on flow limitation, TBM in these patients may worsen symptoms by impeding clearance of secretions and/or causing local air irritation resulting in recurrent infections and airway inflammation.
Interestingly, even though some patients had improvement in the 6MWT scores, the improvement was not clinically or statistically significant. We speculate that it is unlikely that patients would undergo substantial reconditioning after only 2 weeks of symptomatic improvement, and thus we may have conducted follow-up to soon to see any change. We believe, however, that these patients, who could not undergo a pulmonary rehabilitation program before stenting, are now able to do so and a longer follow-up interval therefore may show improvement in exercise tolerance. Active data collection to address this issue is ongoing.
FEV1 is frequently used as a surrogate end point for severity of obstructive lung diseases.2728 In our study, we found that clinical improvement was not associated with significant changes in FEV1 in this population. Median FEV1 decreased by 0.05 L (p = 0.79), with first and third quartiles at – 0.1 and 0.1, respectively.
On the downside, most complications we observed were related to the stents. Airway stents are often associated with reversible short-term and long-term complications. Complications were common in this study and included obstruction (by mucous plugging), infection, and migration with a peak incidence at 3 weeks. These complications were relatively easily managed by therapeutic suctioning, replacement, or removal of the stent and, if infection was a concern, with a 7- to 10-day antibiotic course. We chose to use silicone stents for a variety of reasons. In case of nonresponsiveness to airway stabilization, these stents are easily removed. Also, as other treatment modalities such as surgical placation are becoming available, permanent stenting may not be desirable. Thirdly, metallic stents in malacia patients are generally fraught with failure and complications and in contrast to silicone stents; their removal is problematic and potentially dangerous. For this reason, the Food and Drug Administration in July 2005 had emitted an alert notice for the use of covered and uncovered metallic stents in benign airway disorders (http://www.fda.gov/cdrh/safety).
There are notable limitations to our approach. Not all stented patients were administered both baseline and follow-up measures. In some cases, patient intake was too rapid to permit baseline assessment, while other patients were unavailable to complete all follow-up testing. There may have been factors related to either the indication for, or success of, treatment that were also associated with availability of pretreatment or posttreatment measures. These factors could bias our findings in favor of positive outcomes. Comparison of baseline measurements obtained on patients who also had follow-up measures, with the total baseline sample reveals no significant differences. This suggests that those available for poststent measurement were comparable to the total baseline sample.
Additionally, there is no control group to compare intervention against standard therapy. Since standard medical therapy for TBM is poorly defined, there was no accepted control condition. Patients were only enrolled after maximal medical therapy for comorbidities was provided.
Finally, neither patients nor providers were blinded to diagnosis or treatment. Although we used well-standardized clinical and research tools for outcome measures, the potential for bias due to observer expectations or placebo effect cannot be ruled out.
Conclusions
Airway stabilization with silicone stents can improve symptoms in a highly selected patient population with severe TBM. The majority of our patients had marked improvement in dyspnea, health-related quality of life, and functional status in this short-term study. Patients with COPD and severe TBM may also benefit from a stenting trial. Stenting is associated with a high number of short-term and long-term but generally reversible complications. Despite the obvious limitations, we believe the results of this study are compelling: patients with severe TBM should be considered for airway stabilization, regardless of comorbidities, including COPD. Improvement needs to be carefully documented and in case of unresponsiveness, stents must be removed. Future research should compare stenting to other interventions, such as surgical tracheoplasty, in treating these patients. Additionally, better diagnostic parameters predicting a successful intervention need to be identified. We suggest that evaluation and treatment of tracheomalacia patients be done in experienced centers and all patients be enrolled in prospective outcome databases. A multicenter study with appropriate protocols may be best suited to answer the open questions.
Acknowledgements
We thank William Lunn, MD, Rabih Bechara, MD, Arthur Sung, MD, and Jed Gorden, MD, for assistance with the data collection, and Roger Davis, PhD, and Anantham Devanand, MD, for statistical assistance.
Footnotes
Abbreviations: ATS = American Thoracic Society; BDI = baseline dyspnea index; KPS = Karnofsky performance scale; 6MWT = 6-min walk test; SGRQ = St. George respiratory questionnaire; TBM = tracheobronchomalacia; TDI = transitional dyspnea index
Physiologic studies in the functional bronchoscopies were supported by National Institutes of Health grant HL 52586.
The authors have no conflicts of interest to disclose as they relate to this manuscript.
Received for publication December 19, 2006. Accepted for publication April 27, 2007.
References
This article has been cited by other articles:
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  P. Girard and R. Caliandro Stenting for Tracheobronchomalacia: Treating Images? Chest, March 1, 2008; 133(3): 830 - 831. [Full Text] [PDF]
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