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Tracheobronchial Stents

Dineen, Kevin M. M.D.*; Jantz, Michael A. M.D.; Silvestri, Gerard A. M.D.*

Review
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The past 10 years have yielded impressive advances in the technology involved with tracheobronchial stenting. Each style of stent has proved to be successful in relieving stenosis in the airways. Each new stent has sought to address the weaknesses of those that have preceded it. The results appear to be improving, and the complications are fewer, as technology has advanced. However, no currently available stent is perfect. The ideal stent is one that is easy to insert and remove (if needed), reestablishes and maintains airway patency without migration, allows clearance of secretions, does not stimulate the formation of marked granulation tissue, and is reasonable from an economic standpoint. Refinements in stent design to improve biocompatibility, reduce migration, and reduce granulation tissue formation continue to be needed. Development of stents that are bioabsorbable could remove any concern related to the relative difficulty of removing a stent weeks to months after initial placement for benign tracheobronchial stenosis. Additional research needs to be conducted to find new methods to deal with the vexing problem of granulation tissue formation using currently available stents. We believe that this technology will not stand still. Whether the perfect stent will ever be realized remains an open question. Debate will continue regarding which physicians should be performing stent placement and how to train and accredit those clinicians interested in being able to perform these procedures. Continued efforts need to be made to provide more awareness for the availability of these technologies and to increase access to these procedures to palliate symptoms and improve quality of life for patients with airway disorders.

*Division of Pulmonary and Critical Care Medicine, Allergy and Clinical Immunology Medical University of South Carolina, Charleston, South Carolina; †Division of Pulmonary and Critical Care Medicine University of Florida Health Science Center, Gainesville, Florida, U.S.A.

Address correspondence and reprint requests to Dr. Gerard A. Silvestri, Medical University of South Carolina, 96 Jonathan Lucas Boulevard, PO Box 250623, Charleston, SC 29425 U.S.A.; e-mail: silvestri@musc.edu

TBM, tracheobronchomalacia

After decades of attempts by numerous scientists to visualize the trachea, in 1897 Gustav Killian was able to use his new “bronchoscope” to remove a foreign body from the airway of a patient, thus marking the birth of tracheal endoscopy. 1 In 1915, Brunings and Albrecht 2 used the technology developed by their mentor Dr. Killian to place rubber prostheses into the stenosed tracheas of several patients. In 1933, Canfield and Norton 3 became the first physicians to document the placement of a metal (silver) stent into the larynx of a 2-year-old child with a bony stenosis. In 1965, Montgomery 4 used a special silicone rubber T-shaped tube placed through a tracheostomy to manage subglottic stenosis. Modifications of the Montgomery T-tube and esophageal stents were made in the 1970s and 1980s to allow for use as airway stents. In 1990, Dumon 5 produced a “dedicated tracheobronchial indwelling silicone stent,” which was able to be placed safely via rigid bronchoscopy.

Since the early 1990s, numerous advances have been made in the area of tracheobronchial stenting. The use of the flexible bronchoscope, in addition to the application of new materials (stainless steel, tantalum, nitinol, and polymers), has allowed this field to blossom and find new indications. Although these advances have come rapidly, ongoing efforts will continue to improve the techniques and materials used to create the ideal stent.

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INDICATIONS

The advent of tracheobronchial stents has allowed physicians to improve airway obstruction of both benign and malignant obstructions. Potential indications for stent placement are presented in Table 1. The most common use for these stents is for the relief of malignant obstructive lesions, either by direct endobronchial tumor growth or extrinsic compression by tumor mass or adenopathy. Benign stenoses of the trachea and bronchi related to intubation, inflammation, and granulomatous diseases (tuberculosis and Wegener's) have been treated successfully with stenting. Other benign processes such as tracheobronchomalacia (TBM) and postlung transplantation anastomotic stenoses have also been alleviated with stent placement.

TABLE 1

TABLE 1

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Malignant Airway Obstruction

The most common indication for the placement of tracheobronchial stents worldwide is malignant stenoses. Although stent placement is not a curative procedure, it can improve airway patency substantially, thus relieving dyspnea and potentially improving quality of life. Airway obstruction from either endoluminal tumor or extrinsic airway compression may be relieved with stent placement. Numerous studies using both silicone and metal stents have been published noting improvements in airway patency, pulmonary function, and performance status after stenting procedures. Malignant stenoses from exophytic tumor in the airway may require treatment to increase airway diameter before stent placement. Potential options include laser resection, electrocautery resection, cryotherapy, photodynamic therapy, balloon dilatation, and brachytherapy. Laser resection and electrocautery resection may be preferable to some clinicians, particularly in patients with high-grade obstructions, in that airway patency may be achieved immediately and stent placement may be performed during the same procedure after tumor resection.

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Benign Lesions

Benign Tracheal Stenosis

Prolonged endotracheal intubation may lead to altered tracheal blood flow, resulting in mucosal injury and scarring followed by tracheal stenosis. Tracheal stenosis may also develop in patients with long-standing tracheostomy tubes. In addition, tracheal stenosis may result from inflammatory disorders such as Wegener's granulomatosis and relapsing polychondritis. Patients typically will present with marked stridor and dyspnea. Traditional strategies for repairing these lesions include repeated endoscopic balloon dilatations, which tend to be only temporizing measures; Nd:YAG laser resection; and surgical reconstructive procedures, which are generally considered the gold standard, although some patients will have contraindications to surgery. The earliest efforts at stenting these areas were performed with Dumon silicone stents. Bolliger et al. 6 reported a series of 38 silicone stents placed in 31 patients with excellent tolerance in 27 patients with early and lasting improvement of dyspnea and performance status. The complications noted included stent migration in five cases, otalgia and dysphagia in one case, and one incident of lethal hemoptysis in a patient who had the stent removed after repeated laser therapy. 6 Martinez–Ballarin et al. 7 presented a series of 48 patients who had silicone stents placed with curative intent. Twenty-one of these patients had their stents removed successfully without recurrence and 16 patients had stents remaining in place at the end of the study evaluation. Complications included migration (17.5%), granuloma formation (6.3%), and airway obstruction by secretions (6.3%). 7 More recent studies have shown similar success using a self-expanding (Polyflex) silicone stent, screw–thread silicone stents, self-reinforced poly-L-lactide stents, and expandable metallic stents. 8–11 Given the complexity presented by many of these patients and the variety of means currently available to treat benign tracheal stenosis, a multidisciplinary approach between pulmonologists, otolaryngologists, and thoracic surgeons to decide on the most appropriate use of laser resection, stent placement, and surgical techniques for select patients has been advocated by some authors. 12 The use of self-expanding metal stents for benign disease is controversial and because of their inability to be removed should only be placed as a last resort.

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Tracheobronchomalacia

TBM is a flaccidity of the airways secondary to a weakening of the tracheobronchial cartilage and widening of the posterior membranous wall. This condition is marked by expiratory airway collapse, which can be exacerbated by any activity that results in an increased respiratory effort. This can lead to air trapping, inability to clear secretions, recurrent airway infections, hypercapnia, hypoxemia, and respiratory failure. 13 TBM may be a congenital condition discovered in childhood or an idiopathic disorder diagnosed in adulthood. TBM can also be associated with lung transplantation, relapsing polychondritis, long-standing tracheostomy tube placement, Mounier–Kuhn syndrome, and chronic high-dose steroid use. Treatment of more severe cases of TBM has included continuous positive airway pressure, elongated tracheostomy tube placement, surgical resection of a malacic segment, external splinting, and stent placement. 14 Dasgupta et al. 15 treated 13 patients with TBM with placement of metallic Wallstents. Symptoms improved in all but one patient, and improvements in mean forced expiratory volume in 1 second by 45% and mean forced vital capacity by 35% were noted. 15 Furman et al. 16 reported successful weaning from mechanical ventilation in four of six pediatric patients with TBM after Palmaz metal stent insertion. Improvements in three of four pediatric patients with TBM after placement of Palmaz stents were also noted by Filler et al. 17 Nashef et al. 18 treated five adult patients with TBM with Gianturco metal stents, with functional improvement noted in three patients. After Gianturco stent placement in 19 adult patients with TBM, no changes in pulmonary function testing were observed by Rousseau et al., 19 although cough efficiency improved in 13 patients. Successful treatment of TBM associated with relapsing polychondritis with metal stent placement has been reported by Sarodia et al. 20 and Dunne and Sabanathan. 21

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Endobronchial Tuberculosis

Although the incidence of endobronchial tuberculosis is not known, it is a well-described entity that can cause notable obstruction to the airways. Therapy includes standard antituberculous therapy with or without steroids, surgical resection, laser resection, electrocautery resection, cryotherapy, balloon dilatation, and stent placement. 22 Sowada et al. 23 reported successful use of Gianturco stents for bronchial stenosis related to endobronchial tuberculosis in five patients. Lee et al. 24 demonstrated improvements in both dyspnea and pulmonary function in all four patients treated with Gianturco-type metal stents compared with symptomatic improvement in 11 of 15 patients (73%) treated with balloon dilatation for tuberculous bronchial stenosis. Pulmonary function tests, obtained in 13 patients treated by balloon dilatation, improved in eight patients (64%). 24 Granulation tissue formation was noted in some patients in both studies.

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Postlung Transplantation Stenosis

Despite improvements in anastomotic techniques, airway complications after lung and heart–lung transplantation remain a marked problem. Postoperative donor lung airway ischemia and impaired airway healing are thought to be major factors leading to stenosis at the anastomotic site. In recent series, the incidence of bronchial stenosis has been reported to range from 7 to 17%. 25 Both silicone and metal stents have been used with success to alleviate these obstructions. 26–28 Granulation tissue, if present, may need to be resected before stent insertion. Recurrent granulation tissue after stent placement remains a marked issue.

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Postpneumonectomy Syndrome

This rare complication is characterized by extrinsic compression of the mainstem bronchus between the pulmonary artery anteriorly, and the aorta and thoracic vertebrae posteriorly as a result of the herniation of the mediastinal structures into the vacant hemithorax. It generally occurs within 1 year after a right-side pneumonectomy. Cordova et al. 29 and Nakamura et al. 30 each report a case study of effective treatment of this condition using metallic stents.

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Aortic Pseudoaneurysm

Weiss et al. 31 describe the case of a patient who presented with dyspnea that resulted from left-side bronchial compression. In this case, the extrinsic compression was caused by a pseudoaneurysm of the proximal descending aorta secondary to an intimal ulceration into the underlying media. They were able to reopen the left mainstem bronchus using an expandable metallic stent.

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Tracheoesophageal Fistula

Although some tracheoesophageal fistulas are congenital, the vast majority of them are secondary to malignancy, especially esophageal carcinoma. This complication usually presents with coughing associated with oral intake and recurrent aspiration pneumonia. Stenting of either the esophagus or the airways has been used with success to palliate this condition. In terms of stenting from the airway side, both silicone stents and covered metal stents have been used successfully. When the initial management has consisted of stenting of the esophagus, there have been reports of resultant tracheal obstruction and respiratory compromise. Although debated in the literature, some authors advocate that the preferred method of dealing with these fistulas is to perform double stenting of both the esophagus and the trachea. 32,33

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TYPES OF STENTS

The ideal tracheobronchial stent should possess several vital characteristics (Fig. 1). It should be capable of establishing and maintaining airway patency, it should be easy and safe to place and remove (if necessary), it should be biocompatible, and it should be flexible enough to fit appropriately in irregular anatomy. It should not cause mucosal injury or granulation tissue formation, hamper the ability to clear secretions, migrate from its desired position, or obstruct otherwise patent lumens. 34 As of yet, no stent has been developed that has all of the desirable qualities without any of the undesirable ones. Perhaps this ultimate combination will never be found, but efforts to find it are ongoing.

FIG. 1.

FIG. 1.

There are essentially five types of stents that have been developed and used for tracheobronchial obstructions. The earliest types were composed of silicone, most notably the Dumon or Endoxane stent (Novatech, Abayone, France). The next set of stents used were the uncovered stainless steel stents such as the Gianturco Z (Cook, Bloomington, IN, USA) and the Palmaz (Johnson & Johnson, Warren, NJ, USA) stents, which were the first stents capable of being deployed using flexible bronchoscopy. The second generation of metal stents, comprised of the Wallstent and the Ultraflex (both by Boston Scientific, Natick, MA, USA), represent the third type of stent. These stents are alloy-based mesh or interwoven loop stents that also are available with a polyurethane covering. The covering prevents ingrowth of tumor or granulation tissue through the mesh framework of the stent. The fourth type of stent, bifurcated Y-stents, such as the Dynamic Y-stent (Rusch, Kernen, Germany), has been designed specifically to deal with the anatomic complexities of the central airways and carina. The fifth type of stent is comprised of hybrids of materials such as polyester/silicone (Polyflex, Rusch) and nitinol/silicone (Novastent; Novadis, Saint-Victoret, France) in an attempt to find the as-yet elusive perfect stent. Each of these models has demonstrated positive results, but all have been shown to have complications. Reports on each of these stents have been published in a wide selection of journal articles. Animal model trials with a bioabsorbable stent have also been reported recently. 10 The following is a brief description of each stent type that has been used most commonly, noting the benefits and drawbacks of each as noted in a representative sample of journal articles.

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Silicone Stents

As noted earlier in this article, Dumon 5 introduced the first silicone stent designed specifically for tracheobronchial use in 1990. Since that time, the Dumon or Endoxane silicone stent has been the most widely used stent for both benign and malignant lesions worldwide. This stent is a cylindrical silicone tube with a smooth inner surface and an outer coating of small studs to hold the stent in place. A Y-shaped version has also been developed. Other silicone stents are also available from other manufacturers (Hood Laboratories, Pembroke, MA, USA). Silicone stents essentially must be placed using rigid bronchoscopy and generally are easy to reposition or remove once placed. The most common complications associated with the Dumon stent have been stent migration, poor clearance of secretions, and granulation tissue formation. Dumon et al. 35 reported 7 years of experience using 1,574 stents in 1,058 patients (360 benign and 698 malignant stenoses). Stent migration occurred in 9.5%, granulation tissue formation in 8%, and secretion obstruction in 4%. The benign group had rates of 15%, 18%, and 8% respectively. 35 Other studies have reported stent migration in 5 to 28% of patients, granulation tissue in 1 to 20%, and secretion obstruction in 6 to 17%. 7,36–38 Two deaths have been reported in the literature that have been attributed to acute airway obstruction caused by poor clearance of secretions in patients with indwelling silicone stents. 7,26 Other drawbacks to these stents include the need for rigid bronchoscopic placement (because fewer pulmonologists are being trained adequately in this technique), poor ability to approximate in irregular airways, and a decreased internal diameter resulting from stent wall thickness. Overall, these stents have demonstrated great success in treating obstructing airway lesions and may well be the gold standard for years to come.

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Gianturco Stent

The Gianturco stent was one of the first-developed metal stents and, given its availability earlier than other stents, more literature has been published on this stent than other metal stents. The Gianturco stent is a self-expanding metal stent that consists of a continuous loop of stainless steel formed in a zigzag fashion to produce a cylinder. The stent is available as a single unit or a double unit with two lengths joined together by a metal strut or nylon suture. Small hooks are placed along the proximal and distal ends to anchor the stent to the airway and to decrease migration. The Gianturco stent is fairly rigid and does not mold to more complex airway anatomy. Although used successfully for the treatment of a variety of benign and malignant airway disorders, several complications have been reported with the Gianturco stent. Complications have included stent migration, strut fracture, airway perforation, fatal pulmonary artery erosion, and a notable rate of granulation tissue formation. 34,39 Given the potential complications of this stent and the availability of other stent technologies, we would not recommend the use of the Gianturco stent in either malignant or benign tracheobronchial disorders.

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Palmaz Stent

The Palmaz stent is a balloon-expanded stainless steel mesh developed originally as an intravascular stent. The stent was used initially in pediatric patients, given the availability of smaller diameter sizes (2.5–3.4 mm), 16,40 although case series involving adult patients have been published more recently. 41,42 The Palmaz stent has been used more commonly in patients with benign airway disorders, although it has also been used for malignant airway obstruction as well. The Palmaz stent exhibits plastic rather than elastic properties, meaning that it is unable to regain its original shape or diameter if it is deformed for any reason. 43 Complications reported with the Palmaz stent have included granulation tissue formation, stent migration, stent collapse and airway obstruction, dehiscence of the stent from the bronchial wall, and one case of fatal aortobronchial fistula. 16,40,41,44 Given the mechanical properties of the Palmaz stent and potential complications, we think this stent should not be used in adults and older children with tracheobronchial diseases, although in infants and young children size limitations may currently allow only for the use of the Palmaz stent. The lack of a covered version of the stent is disadvantageous for use in malignant airway obstruction.

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Wallstent

The Wallstent is a self-expandable wire mesh made of cobalt alloy monofilaments. The Wallstent is currently available only in a version with a polyurethane covering, although most publications in the literature have reported the use of the uncovered version. The stent is flexible, compressible, and able to conform to irregular airway geometry. The Wallstent has been used successfully for both benign and malignant airway disorders. 15,45–49 Granulation tissue formation has been the most common complication reported with the Wallstent, with reported rates ranging from 0–18%. 15,45–47 Stent migration and mucus plugging within the stent has not been noted. Staphylococcal bronchitis has been reported in two patients. 15 One notable problem with the Wallstent is a property described as foreshortening. If the stent is compressed, either laterally or circumferentially, it lengthens, which can be problematic because this movement can irritate the mucosa and stimulate granulation tissue formation. 50

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Ultraflex Stent

The Ultraflex is composed of a woven, single strand of nitinol—a nickel–titanium alloy—with a unique shape memory property. 51 This means that the stent deforms plastically in colder temperatures, but regains its original shape when the temperature is increased. The knitted design allows the Ultraflex to adapt well into irregularly shaped or deformed airways. 52 Both uncovered-and polyurethane-covered versions of the stent are available. Because this stent has been released more recently, few studies have been published evaluating the use of the Ultraflex stent. Ducic and Khalafi 53 inserted uncovered Ultraflex stents in six patients, five with tracheal stenosis and one with tracheomalacia with good results. No granulation tissue formation was noted during follow-up. Nicolai et al. 54 reported improvement in respiratory status after placement of Ultraflex stents in five pediatric patients with TBM and benign airway compression. 54 In a study of 34 patients with malignant airway obstruction, Miyazawa et al. 55 noted improvements in dyspnea and pulmonary function tests after uncovered Ultraflex stent insertion. At the time of publication in 2000, Jantz and Silvestri 34 had placed 49 Ultraflex stents into 34 patients over a 2-year period for both benign and malignant lesions. Follow-up of 16 of the patients with benign pathology over a 17 to 31-month period (average, 19.5 months) failed to demonstrate secretion retention or granulation tissue formation. Only one case of migration was noted, and that was in a patient with small cell lung cancer whose extrinsic compression was relieved completely by chemotherapy. 34 A second case of Ultraflex migration was witnessed at the same institution in November 2001 in a patient whose lymphoma responded briskly to radiation therapy, thus removing the tracheal compression and allowing the stent to become freely mobile and expelled by vigorous coughing. The Jantz and Silvestri 34 series noted removal of two Ultraflex stents from a patient whose dyspnea returned 6 months after stent placement. Bronchoscopy revealed dynamic airway collapse despite appropriate stent placement. The stents were removed easily with rigid bronchoscopy and the patient had a Rusch Dynamic Y-stent placed with excellent results. 34 Likewise, Ducic and Khalafi 53 reported their results using Ultraflex stents in six patients without granulation tissue formation and with epithelialization of the stents at surveillance bronchoscopy 6 to 8 weeks later.

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Bifurcated Y-Stents

A recurrent problem faced by interventional pulmonologists is the situation when both mainstem bronchi and the carina are involved, particularly with endoluminal tumor. Traditional stents are at risk for obstructing one mainstem bronchus in efforts to stent the other. The placement of individual stents into each mainstem bronchus in the same patient is possible but leaves the potential for tumor ingrowth from the carina into the stents. Several models have been designed in an effort to deal with this difficult anatomy. A prime example of this type of stent is the Rusch Dynamic Y-stent, also known as the Freitag stent. This stent is an anatomically shaped, bifurcated silicone stent reinforced with embedded U-shaped steel struts and a flexible posterior membrane, which is meant to mimic the membranous portion of the trachea. Freitag et al. 56 reported their 5-year experience using 135 of these stents in patients for malignant compression, tracheoesophageal fistulas, and tracheal stenosis. They reported easy and safe placement and removal, immediate relief of symptoms in most cases, and rare complications. Cephalad stent migration occurred in only 4 of 136 patients (3%). Two patients whose stents were placed to relieve tracheal compression related to aortic abnormalities died of hemoptysis secondary to erosion. Shiraishi et al. 57 treated six patients with severe inoperable tracheobronchial stenosis at the carina with Dynamic Y-stents with immediate relief in five patients. One patient died 3 days after stent insertion secondary to lymphangitic tumor spread. No complications were noted. 57 Other available Y-stents include the Dumon Y-stent (Novatech) and the Hood Y-stent (Hood Laboratories).

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Polyflex Stent

The Polyflex stent consists of a polyester wire mesh covered with a layer of silicone and is placed via rigid bronchoscopy. The stent has elastic recoil and is able to adapt to airway irregularities. The stent is thin walled and has an improved internal/external diameter ratio compared with silicone stents. The Polyflex stent has been available in Europe for a period of time and has recently become available for use in the United States. Few studies have been published evaluating this new stent, however. Wasserman et al. 8 reported their initial experience with the Polyflex stent in 19 patients. Seventeen patients had malignant airway obstruction, five of whom had respiratory–enteric fistulas, and one patient each had benign tracheal stenosis and TBM. Clinical and bronchoscopic improvement was noted in all but one patient. Substantial problems with retained secretions were observed with earlier prototypes. Three episodes of stent migration were noted, and infolding of the inner silicone membrane was noted in two patients.

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Bioabsorbable Stents

Korpela et al. 10 recently published animal model studies of a bioabsorbable stent composed of self-reinforced poly-L-lactide. Poly-L-lactide has a long biodegradation time. The stent demonstrated good biocompatibility and was well tolerated by the animals. To our knowledge, no human trials have been performed with bioabsorbable materials. If developed sufficiently, bioabsorbable stents may have a role in the management of benign airway stenoses.

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BENEFITS OF STENT PLACEMENT

Although stent placement and other bronchoscopic interventional procedures may prolong the life of patients with severe airway obstruction, this has not been proved conclusively in controlled studies. Although stenting techniques may not prolong the life of many patients, the ability to relieve symptoms is a worthwhile outcome. With regard to malignant airway obstruction, stent placement is almost always a palliative procedure for patients who are not candidates for curative resections. Some, but not all, patients with benign airway disorders may be provided with long-term control or “cure” of their disease process by stent placement. For a substantial number of patients with benign tracheobronchial diseases who are not candidates for curative surgical procedures, however, stent placement is again a palliative procedure. To what extent, then, do stenting procedures produce changes in symptoms and quality of life given this is ultimately the goal of the intervention rather than just the ability to increase airway diameter?

Considering the myriad of studies reporting experience with various stents during the past several years, relatively few have evaluated how stent placement affects pulmonary function. Table 258–64 lists several studies that reported changes in pulmonary function tests in patients who received stents for various airway disorders. All but two studies demonstrated improvements in each of the parameters measured. Although not presented, additional studies evaluating pulmonary function after stent placement in combination with laser resection have been published.

TABLE 2

TABLE 2

The most important measure of the success of stenting procedures is related to improvements in the quality of life of the patients after they receive stents. Relatively few studies have evaluated systematically changes in dyspnea and quality of life after stent insertion, and most involve small numbers of patients. In addition, many studies used performance scores, such as the Karnofsky performance score, which may provide an indirect measure of quality of life but are not true instruments for evaluating quality of life changes. We discuss briefly those studies that provide information on performance status and dyspnea.

Wilson et al. 58 treated 56 patients with malignant airway obstruction with Gianturco stents, providing data on performance status and dyspnea for 11 patients. The Medical Research Council dyspnea score improved from 5 points to 4 points (p = 0.02) and the visual analog scale for breathing improved from 40 to 63 mm (p < 0.05). The Karnofsky performance score improved from 29 to 52 (p = 0.002). 58 After placement of Gianturco stents in 22 patients with malignant airway obstruction, Nakajima et al. 65 noted improvement in the Hugh–Jones dyspnea score by more than one grade in 21 patients and improvement in the Eastern Cooperative Oncology Group performance score by more than one grade in 17 patients. Zwischenberger et al. 66 noted improvements in the Karnofsky performance score in four of nine patients treated with Wallstent or Gianturco stents for malignant stenoses. After the insertion of Gianturco stents in 44 patients with malignant tracheobronchial stenoses, Tanigawa et al. 67 observed an improvement of the Hugh–Jones dyspnea score by more than one grade in 35 patients (79.5%). Five of six patients who required intubation before stent placement were able to be weaned from mechanical ventilation afterward. 67 Other studies have also reported changes in performance status and dyspnea after silicone and metal stent insertion in conjunction with laser resection for malignant airway obstruction. 6,48,49,68

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STENT SELECTION AND INSERTION ISSUES

Because stents are used generally for palliative therapy and are not curative, it is very important that several factors be considered by the physician before stent placement. First, and perhaps foremost, is the question of whether the patient actually needs and will benefit from a stent. If the patient is minimally symptomatic and has a benign condition that is not likely to progress (i.e., tracheal stenosis), then subjecting that patient to the risks of the procedure and potential complications of the stent itself may not be a wise endeavor. Likewise, a patient whose malignancy has progressed to a point where their life expectancy is a matter of days to weeks is not an ideal candidate for implantation of a stent. Second, the experience of the physician and the availability of appropriate equipment for the indicated stent placement must be evaluated. Finally, the indication for stent placement, the anatomic site involved, and the size of stent needed are factored in. After analyzing each of these questions, the physician must select the most appropriate stent available, which may require that the procedure be delayed so that the best stent can be ordered if not available at that time.

Several controversial points have arisen with regard to stent placement. Much controversy has been raised in the literature regarding the use of silicone stents vs. metal stents, particularly for benign airway disorders. Jantz and Silvestri 34 argued in favor of using metal stents for benign tracheobronchial disease vs. the silicone stents favored by Rodriguez et al. 69 Benign lesions that may be anticipated to resolve with temporary stenting would be well suited for a silicone stent that can be removed easily. In this instance, for patients with subglottic stenosis or tracheal stenosis that are not operative candidates or decline surgery, silicone stent placement should be strongly considered, recognizing that stent migration may be an issue in these patients. If the patient fails silicone stent placement, metal stent placement may be appropriate. For benign inflammatory stenoses, a covered metal stent may be a better choice than an uncovered metal stent to prevent granulation tissue ingrowth, whereas for pure fibrous stenoses an uncovered metal stent may be appropriate. With regard to tracheomalacia and bronchomalacia, either silicone or metal stents may be used. Metal stents may be more advantageous given their apparent fewer problems with migration and secretion retention. For malignant stenoses, either silicone stents or covered metal stents are appropriate. Uncovered metal stents have the problem of tumor ingrowth through the mesh and should not be used. In the setting of tumor involving the carina and mainstem bronchi, consideration should be given for the use of a bifurcated Y-stent.

There are two schools of thought when it comes to the type of bronchoscopy used for such procedures: rigid vs. flexible. 70,71 Proponents of rigid bronchoscopy argue that the rigid bronchoscope provides better control of the airway and better ability to deal to substantial hemorrhage in the airway, both of which are valid arguments. For patients with severe tracheal stenosis, large tumors occupying the trachea, and bulky carinal tumors obstructing both mainstem bronchi, rigid bronchoscopy does provide marked advantages in dealing with these lesions safely and effectively. For clinicians who use silicone stents, rigid bronchoscopy is essentially the only way to place the silicone stent. Many interventional pulmonologists have argued that stent placement and tumor debulking procedures, such as laser resection, performed before stent insertion can only be done safely via rigid bronchoscopy. On the other hand, there is extensive literature and clinical experience that stent placement can be performed effectively and safely with the flexible bronchoscope for most lesions. At some centers, laser resection is done routinely via flexible bronchoscopy, and other ablative techniques such as electrocautery resection and cryotherapy can be performed safely and efficaciously with the flexible bronchoscope. Being able to do stent placement via flexible bronchoscopy with conscious sedation and topical anesthesia allows for much greater patient access to these palliative procedures because the minority of pulmonologists, particularly in the United States, are currently trained to perform rigid bronchoscopy. Although formal cost-efficacy analysis studies have not been performed, given the costs associated with rigid bronchoscopy, metal stent placement via flexible bronchoscopy may be more cost-effective.

Along these lines, another controversy that is being debated is whether stenting and other airway interventions should be performed in the community or only at specialized, tertiary centers. As noted previously, fewer pulmonologists are trained in rigid bronchoscopy, and a strict belief that only rigid bronchoscopy and silicone stents should be used for airway disorders would limit markedly the number of physicians and centers available to offer these procedures. One can certainly make an argument having patients referred to clinicians that mainly do interventional pulmonology would decrease the incidence of complications and improve patient outcomes. On the other hand, having a limited number of centers available to perform these procedures would likely decrease the number of patients who would undergo these measures as a result of some patients' financial limitations, willingness to travel potentially great distances, and physical ability to travel. In our opinion, particularly with regard to patients with lung cancer, there are a great number of patients who are already not receiving beneficial palliative airway interventions. Limiting the availability of this technology further seems problematic. In light of this, however, if these procedures are adopted by community pulmonologists to increase provision of symptom palliation for their patients, some complications will be expected among physicians who do not do a large number of stent placements, and these complications will require referral to tertiary centers. We do think, however, that patients with benign tracheal stenosis and severe, life-threatening central airway obstruction from malignancies should be considered for referral to specialized centers if possible. A model of community physicians who can perform these procedures with close ties to tertiary care centers seems an appropriate compromise if the art of stent placement is ever going to be widely used. This cannot be accomplished without appropriate training. It is important that fellowship programs begin to incorporate interventional training into the standard fellowship track. Several programs throughout the United States and abroad have begun a 1-year “interventional fellowship,” which follows the usual 3-year pulmonary/critical care fellowship. These types of programs are essential in spreading this expertise worldwide. Others have taken less formal 3 to 6-month sabbaticals at hospitals with expertise and a large volume of cases. Still others get started with 1 to 3-day courses. All of these activities should continue to be encouraged.

The ACCP interventional network is currently establishing guidelines and standards for all interventional pulmonary procedures. Hospitals may adopt these standards to ensure high-quality patient care. We support these efforts.

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REFERENCES

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Keywords:

Stents; Tracheal stenosis; Bronchial stenosis; Tracheobronchomalacia

© 2002 Lippincott Williams & Wilkins, Inc.