Adult Chest Surgery

Chapter 47. Use of Tracheobronchial Stents 

A number of benign and malignant disorders of the upper airways can cause tracheobronchial narrowing, stricture, compression, or collapse (i.e., tracheobronchial malacia), ultimately leading to symptomatic and potentially life-threatening dyspnea. These tracheobronchial compromises can be managed with endobronchial dilation in addition to placement of endotracheal, bronchial, or tracheobronchial stents. Generally, stent placement can be accomplished safely and provides immediate relief of symptoms in the acute setting. Over the long term, stent placement has been shown to improve the patient's quality of life. The use of endobronchial stents has accelerated recently as a result of the proliferation of new biocompatible materials, novel stent designs, and easier techniques for deployment.

Although stents have been described in reports dating back to the 1800s, the concept of using stents to relieve acute tracheobronchial obstruction was not reported until the mid-1950s.1 Dumon designed a dedicated endoluminal upper airway stent in the late 1990s,2 and it remains today one of the most commonly used silicone stents. The self-expanding metal stents manufactured from biocompatible metal alloys also were pioneered in the 1990s using technology initially developed for vascular and coronary stents.3,4 The ideal tracheobronchial stent has yet to be perfected, and there are potentially life-threatening risks associated with all stents currently on the market. Making the correct stent selection therefore is critical for the well-being of the patient.

INDICATIONS FOR ENDOBRONCHIAL STENTS

The indications for deployment of airway stents include (1) extrinsic compression of the central airways with or without intraluminal components owing to malignant or benign disorders; (2) complex, inoperable tracheobronchial strictures; (3) tracheobronchial malacia; (4) palliation for recurrent intraluminal tumor growth; and (5) central airway fistulas (i.e., esophagus, mediastinum, or pleura).

Presenting signs and findings may include dyspnea, cough, hemoptysis, recurrent lung infections, wheezing, and stridor. On occasion, a patient may be referred for evaluation of findings made on a screening CT scan. Since many types of endobronchial therapies are available for patients with airway disorders, it is important to recognize that stenting is just one such modality, and the patient may benefit from a combination of treatments.

DESIRABLE STENT CHARACTERISTICS

The ideal stent should be easy to insert and remove yet resistant to migration. It should be sufficiently strong to support the airway yet flexible enough to withstand (and collapse with) cough without fracturing, narrowing, or moving. The material from which the stent is made should be biologically inert to minimize the formation of granulation tissues. The stent should not change in size when collapsed, or a scar may form at its two ends. The stent should be available in a variety of lengths and sizes, and its walls should be as thin as possible for a maximal intraluminal diameter to prevent retention of secretions. The stent should permit movement of secretions across its surface to prevent inspissation of secretions that could obstruct the stent. Finally, the stent should perfectly appose the airway wall to cover defects and prevent the ingrowth of tissues that may obstruct its lumen without causing airway ischemia or injury.

CLASSIFICATION OF STENTS

Tracheobronchial stents are classified according to their material composition (i.e., plastic, metal, or mixed) (Table 47-1). Plastic tracheobronchial stents usually are made of silicone, which is inexpensive and inert. They have solid walls, which prevent luminal obstruction secondary to tissue ingrowth, and they are removed easily, although rigid bronchoscopy usually is required for their insertion and removal. As a consequence of their relative mobility, plastic stents have a higher rate of migration (10%). They are also somewhat thicker than metallic stents, which limits the intraluminal diameter and increases the probability of having retained airway secretions, particularly with smaller-caliber stents.

Table 47-1. Classification of Stents

Metallic stents

Balloon-expandable metallic stents

·   Palmaz stent

·   Strecker stent

 

Self-expanding metallic stents

·   Gianturco-Z stent

·   Wallstent

·   Nitinol/InStent/Ultraflex stent

 

Silicone stents

·   Dumon stent

·   Hood stent

·   Montgomery T-tube

 

Combination stents

·   Reynder stent

·   Dynamic stent

·   Polyflex

·   Novastent

·   Alveolus (AERO)

 

 

The large number of metallic stents are composed of substances such as stainless steel, alloys that incorporate cobalt and chromium, and Nitinol, a biologically inert titanium and nickel alloy. The most commonly used are the self-expandable metallic stents (SEMS). These stents are stored in the collapsed state and revert to the fully expanded state on release in the correct airway location. Deployment mechanisms vary among SEMS. The walls of SEMS are thinner than plastic, yielding a larger intraluminal diameter, which permits deployment of smaller stents. The stents are quite strong and are designed to last a lifetime. Because the delivery systems are smaller, they can be inserted with a flexible bronchoscope, sparing the necessity of general anesthesia.

SEMS are available in two forms: covered and uncovered. The benefit of the uncovered variety is that within 3–4 months of placement, the stent becomes incorporated in the walls of the trachea or bronchus and lined with a new ciliated epithelial tissue layer, which facilitates the patient's ability to clear secretions. The uncovered metal stent is, for all practical purposes, a permanent prosthesis that permits tissue ingrowth between the metallic components, making it extremely difficult to remove the stent if it fails. For this reason, uncovered SEMS often are not recommended for benign tracheobronchial processes or for patients who are expected to survive for a long time. Covered SEMS were developed specifically to deal with the complication of tumor ingrowth. These are usually coated with Silastic or polyurethane and are essentially identical to the uncovered variety.

Since neither the metallic nor plastic stents have all the desired characteristics of the ideal stent, a number of manufacturers recently have introduced combination stents. These are made partly of metal and partly of silicone or other plastic materials. Nitinol is a component of many of the combination stents.

SPECIFIC FEATURES OF SOME COMMONLY USED STENTS

The two most commonly used balloon-expandable metallic stents are the Palmaz stent and the Strecker stent. The Palmaz stent (Johnson & Johnson, New Brunswick, NJ, and Interventional Systems, Warren, NJ) is reportedly the device used most commonly in children, in part because of its small size. The stent consists of a 150-m-diameter slotted stainless steel mesh tube. It is available in lengths ranging from 10 to 40 mm. A balloon 6–10 mm in diameter fits inside the stent for manual expansion by as much as 6–12 mm. An appropriate size for expansion in children is 8 mm for the trachea and 6 mm for the bronchus. After balloon expansion, the stent ceases to exert outward pressure on the airway wall. The stent has been used in primary tracheomalacia or bronchomalacia, external compression of the trachea or bronchi, and collapse of the trachea or bronchi from previous surgery. Occasionally, it needs to be reexpanded, particularly after a violent coughing fit. The Strecker stent is made of a tantalum filament that is fashioned into a cylindrical wire mesh. The stent is flexible, whether compressed or expanded. When expanded, the stent does not change in length. The Strecker stent is 2–4 cm long and can be expanded by 8–11 mm. This stent has been used successfully in patients with tracheobronchial obstruction.

Specific examples of the SEMS include the Gianturco-Z (William Cook, Bjaeverskov, Denmark), the Wallstent (Boston Scientific Corporation, Natick, MA), and the Ultraflex stent (Boston Scientific Corporation, Natick, MA). The Gianturco-Z is composed of 460-m stainless steel filaments that are arranged in a zigzag configuration. The diameter of the stent when expanded is 15–40 mm.5 The stent is available in 2- and 2.5-cm lengths. In its original design, it has metal hooks to prevent migration. The Gianturco-Z stent has been used to expand the tracheobronchial region in benign disease (e.g., posterior anastomotic strictures, tracheal stenosis, and tracheobronchomalacia). The stent exerts adequate radial force and does not shorten when deployed. It does have a tendency to spring forward if released too quickly. Complications are sometimes reported, including breakdown or unraveling of the stent and fatal hemoptysis after erosion into the pulmonary artery.

The Wallstent (originally the Schneider stent) is a stainless steel device composed of approximately 15–20 braided (100-m-diameter) filaments (Fig. 47-1). The filaments are arranged in a crisscross fashion to form a cylindrical mesh. Stent diameters range from 6 to 25 mm; lengths range from 2 to 7 cm. The stent exerts adequate radial force and is flexible. However, it can shorten to 20–40% of its original size on deployment. An important advantage of using the Wallstent is the ability one has to cut small openings into the mesh when the stent traverses bronchial openings. A disadvantage is that it changes length whenever it is compressed, potentially causing scars and stenosis at its edges.

Figure 47-1.

 

Uncovered Wallstent.

 

Stents made of Nitinol (e.g., Nitinol, InStent, and Ultraflex stent) are thermally triggered and change shape in response to temperature changes (Marmen effect).6 The Nitinol wire is heated, made into a helical shape, and then cooled for deployment. With release into the target site, the high body temperature causes the stent to coil back into its original helical shape. Alternatively, a current of 1.5–3 A or 3–5 V can be applied to the stent for 1–2 seconds until it reaches a temperature of 40°C, causing it to convert to the fully expanded state. Ultraflex stents are configured such that the wire backbone is perpendicular to the airway wall, which prevents substantial shortening or lengthening with changes in airway width and lends considerable stability to the stent (Fig. 47-2).

Figure 47-2.

 
 

Ultraflex stents.

Silicone Stents

The Dumon stent (Boston Medical Products, Westborough, MA) is a cylindrical silicone stent with external studs that are placed at regular intervals to prevent migration and limit contact with the airway wall, thereby reducing mucosal ischemia (Fig. 47-3). Several other varieties of silicone stents are currently available from Hood (Hood Laboratories, Pembroke, MA) (Figs. 47-4 and 47-5) in the United States and other manufacturers worldwide that have slightly different types of posts or rings to reduce migration. All these silicone stents are less expensive than metallic stents, are available in many sizes, and even can be custom manufactured within a few days. Y stents adjusted to cover the distal trachea and both main stem bronchi are also available from most of these manufacturers and can be custom made with respect to sizes and angles. Once placed in the airway, the stent can be adjusted with a forceps and bronchoscope.

Figure 47-3.

 

Dumon stents.

 

Figure 47-4.

 
 

Hood stents.

 

Figure 47-5.

 

Hood stent in bronchus.

 

The Montgomery T-tube, which was introduced in the mid-1960s to support the trachea after laryngotracheoplasty (Fig. 47-6), also can be used for a number of stenting applications. In its original form, the device was an uncuffed silicone T-tube that was inserted with the long limb in the distal trachea, a short limb in the proximal trachea (or in some patients even through the vocal cords), and the T limb projecting through the tracheostomy stoma. Several modifications have been made in the original design to allow for a proximal cuff and other extras, such as a T-Y stent. The T-tube is supplied in sizes ranging from 4.5 to 16 mm (external diameter) and can be custom made as well. Smaller sizes (4.5–8 mm in external diameter) are available for pediatric use.

Figure 47-6.

 

Montgomery T-tubes.

 

Other plastic and combination stents include the Reynder stent (Reynder's Medical Supply, Lennik, Belgium), a cylindrical silicone prosthesis that is more rigid than a regular silicone tube but requires a special introducer and a bronchoscope for placement. The Dynamic stent (Rusch AG, Duluth, GA) is a silicone Y stent with anterior and lateral walls that are reinforced with metal to simulate the tracheal wall. Special forceps are available for insertion within the rigid laryngoscope (Fig. 47-7). The Polyflex (Rusch AG, Duluth, GA) is a self-expandable stent made of polyester wire mesh within layers of silicone (Fig. 47-8). Essentially, this is a silicone stent that can be deployed with flexible bronchoscopy, but rigid bronchoscopy is required for removal. Novastent (Novadis, Saint-Victoret, France) is a thin silicone sheet that contains a small metallic hoop of Nitinol alloy. The silicone bands on the ends are designed to prevent migration.

Figure 47-7.

 

Dynamic Y stent.

 

Figure 47-8.

 

Polyflex stents.

 

The AERO™ stent (Alveolus, Inc., NC USA) is another recent addition to the family of composite stents (Fig. 47-9). It is a combination stent made of a Nitinol metal scaffold covered with a silicone-containing biocompatible membrane to minimize the possibility of tissue ingrowth and granuloma formation. The stent does not foreshorten on delivery, and the hydrophilic coating on the inner lumen of the stent minimizes the possibility of mucous adherence and accumulation.

Figure 47-9.

 

AERO™ tracheobronchial stent system.

PREPROCEDURE ASSESSMENT

Patients should have a chest CT scan for identification of the lesion and measurement of the diameter of the bronchus below and above the area of obstruction, as well as the distance between the desired distal and proximal ends of the stent (Fig. 47-10). The status of the lesion is also assessed via bronchoscopy.

Figure 47-10.

 
 

CT scanning is used to identify the lesion and size the stent. A. Before deployment. B. After deployment.

STENT PLACEMENT TECHNIQUE

Stent Selection

The most important factor in selecting an appropriate stent is the indication. Patients with benign disorders and cancer patients who are expected to survive longer than 1–2 years should have stents that are removable. One of us (Dr. Bueno) strongly recommends against placing a SEMS for nearly any benign condition. The reasoning is that after a few weeks, SEMS incorporate in the tissues, are quite difficult (although possible) to remove, and may perforate into adjacent structures with time.

Patients who undergo stenting for palliation of advanced cancer are candidates for covered stents only, preferably ones that do not migrate readily. The anatomic position of the lesion sometimes dictates the type of stent to be used. For example, a Y stent or a Dynamic stent is required for lesions affecting the carina (Fig. 47-11). It is currently our (Dr. Bueno) practice to place either SEMS or combination stents for all malignant cases. A special example is the malignant inoperable tracheoesophageal fistula. Our preference is to stent the esophagus first with an SEMS or combination stent because this usually solves the problem. If the problem persists, the airway also can be stented with an equivalent stent.

Figure 47-11.

 

Dynamic stent in situ.

 

Finally, size matters. Silicone stents generally are thicker than metallic stents and are more likely to get obstructed with secretions in patients who require a smaller-sized stent. This problem is encountered more frequently with bronchial applications, such as the difficult situation of stenting a distal short stricture without obstructing other bronchi in locations such as the bronchus intermedius. For some patients, there is no good solution, and surgeons should consider cutting a combination stent to the correct size.

Ideally, the surgeon placing the stent should foresee the potential complications and have available a variety of options for managing immediate complications. Thus, in our opinion, expertise with rigid bronchoscopy is mandatory, and a team experienced in the management of airway disorders is very helpful. Patients who require rigid bronchoscopy for stent placement must have general anesthesia, whereas those undergoing stent placement via flexible bronchoscopy do not always require intubation but do require IV sedation. It is our preferred practice to perform stent placement with the support of an anesthetist to keep all options open.

Fluoroscopy is quite helpful in stent placement but not absolutely mandatory. Most stents are marked with radiopaque markers to show distal, proximal, and midstent locations, which can be identified when stents are placed under fluoroscopic guidance. Guidewires usually can be used to guide most stents into the correct position for deployment by a variety of mechanisms depending on the stent that has been selected. A guidewire with a flexible tip is preferred because it is less likely to perforate the bronchus. It is best, if possible, to deploy the stent such that the middle of the stent is in line with the middle of the shelf of obstruction or narrowing (Fig. 47-12). This reduces the risk of migration because the stricture itself will hold the stent in place. Silicone stents usually require specific delivery devices for deployment through the rigid bronchoscope. These cost approximately $10,000 but are useful to have in expert centers.

Figure 47-12.

 
 

Deployment under fluoroscopic guidance.

Once the stent is positioned in the airway, it can be pulled back using a biopsy forceps. It is far easier to place the stent slightly distal to its target location and then pull the stent back into desired position rather than attempt to push the stent into position. It is important to confirm the position of the stent with bronchoscopy, but we do not recommend using an adult bronchoscope for testing any stent with a diameter of less than 12 mm because of the risk of it becoming dislodged.

Once the stent is in position, the patient should get a chest radiograph followed by bronchoscopy within the next 2–4 weeks or earlier if the patient has new symptoms. We recommend a perioperative course of antibiotics as well as daily humidification to reduce the accumulation of inspissated, concreted secretions. Mucomyst and DNase may be added as necessary, as well as steroids, when airway trauma is suspected during stent deployment.

EARLY COMPLICATIONS

Cough is a common side effect after stent placement and usually disappears. It responds well to codeine-containing elixirs. Excessive coughing can cause the stent to dislodge, particularly when there is no stricture shelf to hold the stent in place. Although generally not dangerous, stent migration and dislodgment are quite traumatic and terrifying to the patient. Cough also can indicate an obstructed or inadequately placed stent and may require a repeat bronchoscopy for assessment.

Obstruction of the bronchial orifices is another potential complication of stent placement and usually results from incorrect preoperative estimation of length or diameter. This condition is often asymptomatic, although on occasion it can cause localized wheezing as air passes through the mesh of the stent. The stent may become impacted with secretions, giving rise to dyspnea owing to mucus plugging. Patients are also at increased risk of developing pneumonia. The malpositioned stent should be removed and replaced with a correctly sized stent to avoid further complications.

Iatrogenic perforation of the airway wall is always a risk and warrants caution and careful follow-up. It is often a fatal complication.

Stent migration may occur, particularly if undersized stents have been used, and can lead to airway obstruction, infections, or persistent cough. This is more likely to occur in patients with malacia or other nonstricture diseases, where the stent is not held firmly in place.

LATE COMPLICATIONS

Tumor regrowth through the stent mesh causing recurrent obstruction is more common with malignant processes and can be avoided by using a covered stent. Proximal migration of the stent is more common with fixed-diameter stents (e.g., the Palmaz stent) and is observed more often in patients who receive radiation and chemotherapy after stent placement.

Rigid metal stents (e.g., Strecker or Palmaz stents) can erode into nearby blood vessels causing hemoptysis. For this reason, stents should be used cautiously, if at all, when the airway obstruction is caused by compression from a nearby vessel. We have treated two patients who survived after developing a fistula from an airway stent into the pulmonary artery merely by placing a pulmonary artery stent to cover the hole.7

Although aneurysmal disease, previous aortic surgery, and neoplasm are the most common causes of aortobronchial fistula, chronic inflammation from an indwelling endobronchial stent, as well as bronchomalacia from recurrent infection, may predispose to the formation of fistulas. Formal graft repair of the aorta with or without pulmonary resection is the classic treatment. Most patients with this condition, however, are too high risk for such an extensive procedure. Although there is risk of infection, endovascular exclusion of the fistula provides a safe and effective alternative for high-risk patients.

Granuloma formation at either end of the stent or growing through the interstices of the stent is the most common complication of expandable metallic stent placement and probably results from an inflammatory response. These granulomata can be ablated using the neodymium:yttrium-aluminum-garnet laser therapy delivered by means of a flexible bronchoscope.

Halitosis is a distressing and difficult complication to resolve. Previous studies have suggested that this condition is secondary to chronic bacterial infection of the stent. Madden and colleagues found that patients with halitosis usually have covered stents, which may provide a suitable environment for bacterial growth and prevent effective mucociliary clearance.8

The cause of chronic chest pain is not fully understood, but it could be attributed to the presence of a foreign body (i.e., the stent) within the airway lumen leading to chronic irritation or polychondritis of the tracheal rings.

SUMMARY

Recent years have seen a proliferation of stents available for airway application. However, no single stent is perfect for all indications. It is therefore important to develop some expertise with various types of stents rather than placing the same brand in every patient notwithstanding the patient's diagnosis. Stent placement can provide immediate relief of symptoms for the acute management of tracheobronchial obstruction irrespective of cause and demonstrates long-term improvement in quality of life. It is one of many endoluminal therapies of the airways, and those interested in placing stents should become educated about alternative therapies as well as potential complications. Of the three major types of stents (i.e., silicone, metal, and combination), silicone stents are the most inert and can be removed easily. Metallic stents are very easy to deploy but can cause long-term irreversible complications. Since the ideal tracheobronchial stent suitable for all purposes is yet to be developed, selection continues to be based on patient factors, surgeon preference, and characteristics of the underlying pathology.

CASE HISTORY

A 62-year-old man with a history of locally advanced lung cancer (stage IIIB) previously treated with chemotherapy and radiation therapy presented with dysphagia and dyspnea. On examination, he had left-sided wheezing. His chest CT scan demonstrated severe narrowing of the left main stem bronchus and esophagus. Bronchoscopy confirmed these findings. He underwent placement of an Ultraflex covered endobronchial stent and an Ultraflex esophageal stent with resolution of symptoms, enabling him to tolerate additional chemotherapy (Fig. 47-13).

Figure 47-13.

 
 

Ultraflex stent deployment system.

REFERENCES

1. Sterioff S: Etymology of the world "stent." Mayo Clin Proc 72:377–9, 1997.[PubMed: 9121189]

2. Dumon JF: A dedicated tracheobronchial stent. Chest 97:328–32, 1990.[PubMed: 1688757]

3. Wright K, Walace S, Charnsangavej C, et al: Percutaneous endovascular stents: An experimental evaluation. Radiology 156:69–72, 1985.[PubMed: 4001423]

4. Stohr S, Bollinger C: Stents in the management of malignant airway obstruction. Monaldi Arch Chest Dis 54:264–8, 1999.[PubMed: 10441984]

5. Duprat G Jr, Wright KC, Charnsangavej C, et al: Self-expanding metallic stents for small vessels: An experimental evaluation. Radiology 162:469–72, 1987.[PubMed: 3797661]

6. Wayman C, Shimizu K: The shape memory (Marmen) effect in alloys. Metal Sci J 6:175–83, 1972. 

7. Davison BD, Ring DH, Bueno R, Jaklitsch MT: Endovascular stent-graft repair of a pulmonary artery-bronchial fistula. J Vasc Intervent Radiol 14:929–32, 2003.[PubMed: 12847202]

8. Madden BP, Loke TK, Sheth AC: Do expandable metallic airway stents have a role in the management of patients with benign tracheobronchial disease? Ann Thorac Surg 82:274–8, 2006.[PubMed: 16798229]



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