Ann Thorac Surg 2007;84:1870-1877. doi:10.1016/j.athoracsur.2007.07.026
© 2007 The Society of Thoracic Surgeons
Original Articles: General Thoracic
Complications of Silicone Stent Insertion in Patients With Expiratory Central Airway Collapse
Septimiu D. Murgu, MD*,
Henri G. Colt, MD
Department of Medicine, Pulmonary and Critical Care Medicine, University of California School of Medicine, Irvine, California
Accepted for publication July 11, 2007.
* Address correspondence to Dr Murgu, UCI Medical Center, 101 The City Drive South, Bldg 53, Rm 119, Rt 81, Orange, CA 92868 (Email: smurgu{at}uci.edu).
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Abstract
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Background: Silicone stent insertion is an alternative treatment for expiratory central airway collapse. This study evaluates the complications (mucus plugging, migration, and granulation tissue) associated with stenting in patients who failed medical therapy and were not surgical candidates.
Methods: Chart review from 15 consecutive patients treated by silicone stent insertion was done over a 2-year period. Outcomes included (1) changes in functional class, extent and severity of airway collapse (graded from 1 to 4 by using a multidimensional system), procedure- and stent-related complications at 48 hours after stent insertion; (2) frequency of stent-related complications; and (3) frequency of emergent flexible and rigid bronchoscopy (scheduled or emergent) over the follow-up period.
Results: Mean functional class and severity and extent of airway collapse significantly improved within 48 hours after treatment (p < 0.05). There were no perioperative deaths. Stent-related complications within 48 hours after stent insertion occurred in 3 patients (1 granulation, 1 migration, and 1 mucus plugging). The mean duration of follow-up for the 12 patients who underwent clinical and bronchoscopic follow-up was 188 days. Twenty-six stent-related complications (12 mucus plugs, 8 migrations, and 6 granulation tissues) were seen in 10 of the 12 patients. Five emergent flexible bronchoscopies and 14 rigid bronchoscopies (6 of which were emergent) were performed during the follow-up period.
Conclusions: Silicone stent insertion improves functional status immediately after intervention in patients with expiratory central airway collapse, but is associated with a high rate of stent-related complications and need for repeat bronchoscopic interventions.
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Introduction
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Patients with expiratory central airway collapse often have debilitating dyspnea, cough, inability to clear secretions, and even respiratory failure requiring mechanical ventilation [1–3]. These symptoms are attributed to flow limitation from excessive narrowing of the trachea and mainstem bronchi during exhalation that results from tracheobronchomalacia and excessive dynamic airway collapse [4]. Expiratory central airway collapse is traditionally diagnosed by bronchoscopy but new imaging techniques, including paired dynamic inspiratory-expiratory computed tomography and cine–magnetic resonance imaging offer a noninvasive assessment of the central airways and allow objective quantification of the degree of airway narrowing [5–7]. Treatment alternatives include conservative medical management of the underlying condition, noninvasive positive pressure ventilation to splint open the airways, airway stent insertion, and surgical stabilization using membranous wall tracheoplasty in severe cases [8].
While tracheoplasty has proven to be a durable and efficacious treatment, only a minority of patients are indeed candidates for this complex surgical procedure [9]. In addition, severe comorbidities may preclude surgery in many cases. One alternative to surgery for patients with severe symptoms is airway stent insertion. Airway stents have been shown to restore and maintain airway patency in patients with various forms of central airway obstruction [10, 11]. Results in patients with expiratory central airway collapse remain uncertain, however, because most published reports of airway stenting also include patients with other causes of benign and malignant central airway strictures [12–15].
Numerous studies demonstrate that stents are effective and relatively well tolerated, although adverse events such as mucus plugging, granulation tissue formation, and stent migration occur in 4%, 8%, and 10% of cases, respectively [16]. Stent-related complications occur more frequently in patients with benign causes of airway obstruction compared with those with malignancies [16, 17].
Because the dynamic features of expiratory central airway collapse continuously alter the shape of the central airways as well as the contact between a stent and the airway walls, one might presume that stent-related complications occur more frequently in this setting. The purpose of this study, therefore, was to determine the frequency and types of stent-related adverse events in patients with expiratory central airway collapse who failed medical therapy and were not surgical candidates for reparative surgery.
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Patients and Methods
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Patients with a known diagnosis of expiratory central airway collapse were extracted from the interventional pulmonology database at University of California, Irvine Medical Center (UCIMC). All patients had been referred to our institution for airway stent insertion after conservative medical therapy including bronchodilators and continuous positive airway pressure failed and were deemed not to be candidates for surgery. Medical records, bronchoscopy photos, and videos of 15 consecutive patients who underwent airway stent insertion for expiratory central airway collapse at UCIMC between 2003 and 2005 were thus reviewed. The Institutional Review Board of UCIMC approved the protocol. Informed consent was not required for this retrospective analysis, but patient confidentiality was protected.
In all cases, diagnosis had been confirmed by dynamic flexible videobronchoscopy performed using moderate sedation with topical anesthesia, regardless of whether the patient was intubated. In some cases, diagnosis was aided by inspiratory-expiratory dynamic computed tomography of the chest to evaluate the adjacent pulmonary parenchyma as well as to evaluate for possible extrinsic vascular or tumor compression (Fig 1). All patients were discussed prospectively in a multidisciplinary chest conference that includes two cardiothoracic surgeons.
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Fig 1. Paired inspiratory-expiratory dynamic computed tomography from patient 14 with focal, severe tracheomalacia from sarcoidosis. (A) Tracheal lumen during inspiration before stent insertion. (B) Tracheal lumen is completely closed during expiration before stent insertion. (C) Tracheal lumen during inspiration after silicone stent insertion. (D) Tracheal lumen patency is maintained by the stent during expiration.
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All interventional bronchoscopic procedures were performed under general anesthesia in a dedicated operating room. After induction, patients were intubated with an EFER-Dumon rigid bronchoscope (Bryan Corp, Woburn, Massachusetts). Patients were ventilated through a side port of the bronchoscope. Anesthesia with spontaneously assisted ventilation was maintained using intravenous propofol. Fraction of inspired oxygen varied between 0.35 and 1.0, and was adjusted in function of transcutaneous oxygen saturation level. The site of airway collapse was carefully inspected. In cases of malacia associated with bronchial or tracheal strictures, the abnormal airway was gently dilated using rigid bronchoscopes of progressively increasing diameter as needed. The distal margins of the stricture were visualized, and total length and diameter of the collapsed airway segments were recorded. Endobronchial lesions and granulation tissue, if present, were coagulated or vaporized using Nd-YAG laser (power settings, 20 to 40 W; 1 s pulses with a laser tip distance from target tissues of 0.5 to 5 mm). Type, length, and diameter of airway stents were determined after measurement of the length and postdilation diameter of the narrowed region. Airway stents inserted were either studded (Bryan Corp), ringed (Hood, Woburn, Massachusetts), or Y silicone stents (Bryan Corp). Stents were inserted through the rigid bronchoscope or using a specially designed forceps (Rusch, Karl-Storz, Germany). Patients were followed up by scheduled outpatient visits and surveillance flexible bronchoscopy. To prevent mucous plugging, it is our practice to prescribe nebulizer treatments using 10 mL saline solution for 15 minutes four times daily. To our knowledge, however, the effectiveness of such treatments has not been studied. Patients are also taught to huff rather than to cough to help clear the airways of retained secretions.
According to our protocol, all patients had been classified according to a multidimensional system (FEMOS [functional class, extent, morphology, origin, severity]) before stent insertion. Patients’ functional status, extent of collapsed airway segment, morphology of the tracheobronchial collapse, and origin and severity of airway collapse were thus assessed (Table 1) [18, 19]. Postprocedure outcome variables included (1) changes in functional status, extent of airway narrowing, and severity of airway collapse within 48 hours after stent insertion as compared with preprocedure findings; (2) perioperative procedure-related complications within 48 hours after stent insertion; and (3) frequency of stent-related complications (migration, mucus plugging, and granulation tissue) including need for repeat emergent flexible or rigid bronchoscopy (emergent or scheduled) during the long-term follow-up period.
Statistical Methods
Measurements of functional class, extent of airway narrowing, and severity of airway collapse before and within 48 hours after stent insertion were compared using the paired t test. A value of p less than 0.05 was considered significant. Analysis of variance (ANOVA) was used to explore the correlations of complication rates with number of stents inserted, and extent and severity of airway collapse. Descriptive statistics were used for all endpoints.
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Results
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Between 2003 and 2005, 15 patients with expiratory central airway collapse (11 males and 4 females) were referred to UCIMC for silicone stent insertion. The mean age (±SD) was 61.6 years (±15.2; range, 29 to 89). Presenting symptoms, underlying etiology, morphologic types as well as functional class, extent of airway narrowing, and severity of airway collapse before and immediately after stent insertion are noted in Table 2. Reasons for inoperability were (1) surgery not indicated (patients 1, 2, and 13 had extensive tracheobronchomalacia caused by relapsing polychondritis); (2) respiratory insufficiency and significant comorbidities including congestive heart failure, chronic renal insufficiency (patients 3 and 8), severe ventilatory restriction and forced ventilatory capacity (FVC) of 30% predicted accompanied by severe kyphoscoliosis requiring spinal fusion (patient 4), and severe coronary artery disease (patient 7); (3) cancer with history of lung resection (patients 9 and 10), advanced cancer with superior vena cava syndrome (patient 12), and history of pneumonectomy in a patient with severe obstructive ventilatory impairment, forced expirataory volume in 1 second (FEV1) 35% predicted (patient 11); (4) presence of focal expiratory central airway collapse and mild functional impairment (patients 14 and 15); and (5) moderate functional impairment with diminished pulmonary function (patient 5 had FEV1 of 20% predicted, and patient 6 had FVC and total lung capacity of 54% and 56% predicted, respectively).
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Table 2 Clinical and Bronchoscopic Data Before and Within 48 Hours After Stent Insertion in 15 Patients With Expiratory Central Airway Collapse
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Overall, a total of 22 stents were inserted in 15 patients (mean, 1.46 stents per patient). All stents were made of silicone and included straight studded Dumon-type stents (n = 18), Y stents (n = 2), and ringed Hood stents (n = 2). Before stent insertion, functional class was classified as severe in 9 patients, moderate in 4 patients, and mild in 2 patients (Table 2). Mean functional class significantly improved from 3.46 to 2.26 (p = 0.0001) after treatment. The severity of airway collapse was classified as severe in 13 patients, moderate in 1 patient and mild in 1 patient. Mean severity of airway collapse scores decreased from 3.8 to 1.4 (p < 0.0001) after stent insertion (Fig 2). Extent of airway narrowing was classified as diffuse in 6 patients, multifocal in 3 and focal in 6 patients (Table 2). The mean extent of airway narrowing score diminished from 3 to 1.5 (p < 0.0001) after intervention. Types, sizes, location, and number of airway stents inserted are shown in Table 3.
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Fig 2. Tracheal lumen images during bronchoscopy from patient 14: before stent insertion (A) inspiration and (B) expiration; and after stent insertion (C) inspiration and (D) expiration.
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There were no perioperative deaths. Immediate stent-related complications within 48 hours, however, occurred in 3 patients (patients 3, 7, and 13), all of whom had respiratory failure upon referral to our institution. Stent-related complications in these 3 patients included granulation tissue formation that could be removed using flexible bronchoscopy at 24 hours in 1 patient (patient 3), stent migration (patient 7), and mucus plugging (patient 13) requiring emergent rigid bronchoscopy at 48 hours and 24 hours in 2 others, respectively.
All 15 patients had follow-up beyond 48 hours, although bronchoscopic follow-up occurred in 12 of the 15. The 3 patients who did not have bronchoscopic follow-up died: patient 8 died 1 month after intervention of acute hypoxemic respiratory failure at an outlying hospital. Patient 10 had progressive weakness and weight loss and died 3 months after stent insertion. Patient 12, who had known mediastinal tumor and superior vena cava syndrome, sustained a cardiorespiratory arrest at home 3 days after discharge from our medical center.
For the 12 remaining patients who had clinical and bronchoscopic follow-up, the mean duration of follow-up was 188 days (range, 6 to 780). A total of 26 stent-related adverse events were noted in 10 of these 12 patients (83%) at a median of 29 days after intervention: 6 cases of granulation tissue formation, 8 stent migrations, and 12 cases of partial obstruction from mucus plugs. The ANOVA did not show any significant correlation between the number of complications noticed during the follow-up period and the number of stents initially inserted (p = 0.16), nor the extent (p = 0.07) or severity of airway collapse (p = 0.14) as initially assessed using the multidimensional classification.
Overall, 29 surveillance flexible bronchoscopies were performed at a median of 40 days after stent insertion; 8 (27%) prompted the routine scheduling of a rigid bronchoscopy. Five emergent flexible bronchoscopies were necessary, of which 1 (20%) prompted an emergent rigid bronchoscopy to manage granulation tissue and post–obstructive pneumonia (patient 1); the other 4 emergent flexible bronchoscopies were to remove mucus plugging (3 for patient 6 and 1 for patient 11). Six rigid bronchoscopies were performed emergently because of new symptoms.
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Comment
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Treatment for patients with expiratory central airway collapse depends on severity of functional impairment, etiology, severity of airway narrowing, and extent of airway collapse. Many patients present with signs and symptoms of respiratory insufficiency that must be treated emergently. In less severe cases, conservative therapy with bronchodilators or continuous positive airway pressure may improve symptoms [20, 21]. Other times, patients are diagnosed while relatively asymptomatic and therefore do not require treatment [22].
For severe cases and for patients who fail conservative therapies, several surgical procedures have been proposed [8]. Tracheostomy offers a secure airway and may bypass the malacic airway segment, but can occasionally be complicated by secondary malacia or stenosis [23] and may actually worsen expiratory collapse because it bypasses the physiologic function of the glottis to maintain positive transmural pressure and airway patency [24]. In patients with clear cases of focal malacia, tracheal resection with end-to-end anastomosis, in experienced centers, is associated with good results [25].
Membranous tracheoplasty has been recently advocated thanks to the successful results reported by Wright and coworkers [9]. The technique involves restoring the proper anatomic configuration of the airway so that the cartilages are brought into a more normal C shape from their flattened pattern. This is done by reinforcing the posterior membrane with a polypropylene mesh which becomes permanently incorporated into the membranous wall through tissue in growth and fibrosis [9]. As of this writing, however, this procedure is limited to specialized centers and is only offered to a small group of patients judged to be ideal surgical candidates.
An acceptable alternative to surgery is therefore desirable for patients with severe disease who are not good surgical candidates or who have failed other therapies. Stent insertion has been shown to successfully maintain airway patency [10, 11, 26], but published experience specifically in patients with expiratory central airway collapse is limited, and includes patients with central airway obstruction from other causes [12–15]. In addition, whereas silicone stents have excellent force compression characteristics and are easily removable in case of complications [10, 27], several investigators report results from metal stent insertion [28–30]. The propensity to fracture and cause granulation tissue formation, however, as well as the difficulty with which metal stents can be removed, has prompted the Food and Drug Administration to release a warning regarding their use in patients with benign disease [31]. Because of potentially life-threatening or fatal complications associated with metal stents, and because of published FDA warnings, we do not advocate using metal stents in patients with benign disease unless all other alternatives have been exhausted. Thus, we did not insert metal stents in our study patients.
The results from our study demonstrate that many patients with expiratory central airway collapse who are not surgical candidates can immediately benefit from silicone stent insertion in terms of improvement in functional status, decrease in the extent of airway narrowing, and severity of airway collapse. Stent-related adverse events, however, were common and usually occurred within the first few weeks after stent insertion (median of 29 days). This supports a practice of early surveillance bronchoscopy in patients with expiratory central airway collapse. Indeed, the overall frequency of stent-related adverse events was much higher than the frequency reported for patients with fixed airway obstruction [16]. We submit that these findings support a hypothesis that the dynamic features and frequently inflamed airway mucosa associated with expiratory central airway collapse puts patients at higher risk for stent related adverse events. In view of the high rate of stent-related complications in this population, we believe that stent insertion should be reserved for patients with significant functional impairment.
Neither the extent of airway narrowing nor the severity of airway collapse or the number of stents employed correlated, however, with rate of complications. This seems counterintuitive, as one might expect a higher rate of complications in patients with diffuse severe airway collapse requiring multiple stents. On the other hand, once symptoms, extent of airway narrowing, and severity of airway collapse are improved by stent insertion, it appears that complications are strictly related to the presence of the indwelling stent.
Undoubtedly, the dynamic features of expiratory central airway collapse can make the selection of the type and size of the stent being inserted problematic. For example, we used Y-shaped stents infrequently because we tried to preserve as much normal mucosa as possible, and thus decrease the likelihood of stent obstruction by tenacious mucous secretions. The Y-shaped stents do not migrate, and hence we believe that had we chosen to insert more Y-shaped or L-shaped stents (stenting only the lower third of the trachea and the involved main bronchus for example), the rate of migration would have been significantly reduced. From a technical standpoint, however, this strategy is not as straightforward as it first appears. Insertion of Y- and L-shaped stents can be difficult, and potentially more dangerous than straight stent insertion, especially if the patient’s airway mucosa is severely inflamed and friable. In addition, inserting these larger stents (often with stent diameters of 16 mm or above) can be difficult using the rigid bronchoscopy equipment available. Only recently has a large stent loading apparatus come on the market that allows easier loading and deployment of these stents into the compromised airway. Data pertaining to mucus plugging related to Y-stents are not available. The Y- or L-shaped stents, however, have less chance of migration and may be warranted in these patients instead of multiple straight stents especially for patients with diffuse disease. Although these stents may cause more mucus plugging, this complication (the most common one in our series) is readily treated by flexible bronchoscopy.
In spite of our using mostly straight silicone stents, mucous plugging was, indeed, the most common adverse event noted in our study, and when detected on emergent flexible bronchoscopy for respiratory distress, could almost always be resolved using flexible bronchoscopy. Stent migration, on the other hand required rigid bronchoscopy for stent revision. Granulation tissue formation also prompted rigid bronchoscopy for laser resection or electrocautery removal, but could also have been treated using flexible bronchoscopic techniques [11]. These results support a hypothesis that the continuous friction between silicone stents and the airway wall of patients with expiratory central airway collapse increases the risk for stent migration and granulation tissue formation. This process may explain the surprising development of granulation tissue in a single patient at 24 hours after intervention. A similar increased rate of silicone stent-related complications has been previously reported with other benign forms of airway obstruction, such as tracheobronchial stenosis after tuberculosis [32]. Treatment algorithms proposed by us [8] and others [22] suggest that stents should be removed if the quality of life and functional status do not improve after the procedure. A lack of improvement, however, may be explained by associated complications (ie, mucus plugging), or physiologically: flow-limiting segments may actually migrate distal to the airway stents, or may be peripheral, in which case splinting the central airways appears to have no impact on patient symptoms. Although expiratory central airway collapse may worsen in some patients, in others there is stabilization [2, 33], such that stent removal might be considered if symptoms and severity of airway collapse are improved. Bronchoscopic and radiographic examination, in addition to careful clinical assessment, using, for example, the classification system described in this manuscript, would allow before and after treatment comparisons.
In summary, silicone stent insertion in patients with expiratory central airway collapse refractory to medical therapy who are not surgical candidates improves functional status immediately after intervention, but is associated with a high rate of stent-related adverse events and need for repeat flexible or rigid bronchoscopic interventions. Prospective studies are necessary to help determine which types and models of stents are most advisable for use in these patients, and to better determine algorithms of care in which bronchoscopy might occupy an important place.
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Abstract
Introduction
