Pulmonary Medicine

Interventional Bronchoscopy: Airway Stents

General description of procedure, equipment, technique

Airway Stents

Initially defined in 1995 and subsequently in European Respiratory Society (ERS) and American Thoracic Society (ATS) guidelines, interventional pulmonology is "the art and science of medicine as related to the performance of diagnostic and invasive therapeutic procedures that require additional training and expertise beyond that required in a standard pulmonary medicine training program." Clinical entities encompassed in the discipline include complex airway management, benign and malignant central airway obstruction, pleural diseases, and pulmonary vascular procedures.

Diagnostic and therapeutic procedures that pertain to these areas include rigid bronchoscopy, transbronchial needle aspiration, autofluorescence bronchoscopy, endobronchial ultrasound, transthoracic needle aspiration and biopsy, laser bronchoscopy, endobronchial electrosurgery, argon-plasma coagulation, cryotherapy, airway stent insertion, balloon bronchoplasty and dilatation techniques, endobronchial radiation (brachytherapy), photodynamic therapy, percutaneous dilatational tracheotomy, transtracheal oxygen catheter insertion, medical thoracoscopy, and image-guided thoracic interventions. This presentation focuses on airway stent insertion; additional procedures are discussed elsewhere.

The term "stent" honors the nineteenth-century British dentist, Charles R. Stent, who developed a dental impression material that was later used as a template to support healing skin grafts. Today, the term connotes an artificial support that maintains patency of a hollow tubular structure. When a large airway is compressed by an extraluminal lesion, airway stents play an important therapeutic role. Although there is no ideal stent, important attributes of the device include ease of insertion and removal, the absence of a proclivity to migrate in the airway, capacity to withstand compression from external forces, minimal tendency to elicit reaction in the surrounding tissue, and the capacity to permit mobilization of respiratory secretions.

Types of Stents

Tracheobronchial stents include those made of silicone (Montgomery T-tube, Dumon, Polyflex, Noppen, and Hoodor), those made of covered or uncovered metal (Palmaz, Wallgraft, Ultraflex), and hybrid stents, which are a combination of the two (Orlowski and Dynamic).

Silicone stents: The most widely used stent for central airway obstruction is the silicone stent. Silicone, a synthetic substance made of silicone elastomers, is firm and stable at high temperatures, and it repels water. Silicone stents are relatively inexpensive and are well tolerated, and they can be repositioned and removed without difficulty. Disadvantages include their tendency to migrate and induce granuloma formation and mucus plugging, insufficient flexibility to conform to irregular airways, interference with mucociliary clearance, and the need for rigid bronchoscopy for their placement.

Metal stents: A variety of metals, including stainless steel, tantalum, and alloys that incorporate cobalt, chromium, and molybdenum (Vitallium, Nobelium), are inherently inert and may be safely placed in living tissues. All metal stents are radio-opaque, and all exhibit varying degrees of dynamic expandability, are easy to insert, and maintain ventilation when placed across lobar orifices.

Metal stents include fixed-diameter stents, which require balloon dilatation, and self-expandable stents, which "spring" to a predetermined diameter once released. The stents are made of bare metal or have a thin coating of silicone, nylon, or polyurethane.

Metallic stents have gained popularity because of their ease of insertion. In addition, they may be placed in an outpatient setting via flexible bronchoscopy under local anesthesia. Advantages of metal stents in management of malignant tracheobronchial obstruction include their thin walls (relative to silicone stents) and their ability to conform to tortuous airways. Metal stents rarely migrate within the tracheobronchial tree (<1%). Similar to the silicone stents, however, metal stents may induce granulation tissue formation. Other disadvantages are that they are difficult to remove and their stent wires have the potential to fracture.

Choice of Stent

Proper selection of stent type and size is critical to avoiding stent-related complications, such as migration, granulation tissue formation, and airway perforation from excessive radial force of the stent, as is the selection of stent length and diameter in relation to tracheal or bronchial size.

Metal stents are more expensive than silicone, and they are difficult, if not impossible, to remove. However, silicone stents require specialized equipment for placement, as well as rigid bronchoscopy, while metal stents may be inserted using flexible fiberoptic bronchoscopy. Even so, proper choice of a stent should not be based on ease of placement; the proper choice is the best stent for a given condition. For benign strictures, only silicone stents should be used, as they are easy to remove and replace.

Immediate and long-term complications should be considered before placing a stent. A useful "check list" in considering stent placement includes answers to the following questions:

  • Is a stent required?

  • Will the patient benefit from stent placement in terms of quality of life or prognosis?

  • Will the stent interfere with or prohibit a curative surgical procedure later?

  • Does the operator have the expertise, equipment, and team to place the stent?

  • What is the underlying airway pathology and which stent is ideal for that pathology?

  • Is it safe to place a stent in the anatomic site?

  • What are the required stent dimensions (length and diameter)?

  • Does the operator have the optimal stent, or should a more appropriate one be obtained?

Indications and patient selection

Stents may be used alone or in conjunction with other techniques for palliation of dyspnea, cough, or respiratory insufficiency that is due to central airway obstruction. An airway stent supports the airway wall against collapse or external compression, and it may impede extension of tumor into the airway lumen. Stents may be safely used in patients who are undergoing external-beam radiation therapy or brachytherapy.

The preferred therapy for a benign strictures that are due to prolonged intubation or infectious or inflammatory diseases is surgical repair, but stenting should be considered if co-morbid conditions preclude surgery. An FDA "Black Box" warning has been established for placing metal stents in patients with benign strictures.

Contraindications

The FDA has recommnended that a metal stent should not be placed in a benign stricture.

Details of how the procedure is performed

Bronchoscopy should be performed in patients with symptoms or radiographic findings suggestive of tracheobronchial stenosis. When a stenosis is discovered, its distance from the vocal cords and the length and diameter of the lesion should be documented. A spiral CT scan with three-dimensional reconstruction is extremely helpful in the sizing of the stent needed, but the largest possible prosthesis should be selected. If a lesion is not amenable to endoscopic removal, bronchial dilatation should be done to enable insertion of a stent of the largest diameter possible.

Interpretation of results

Not applicable.

Performance characteristics of the procedure (applies only to diagnostic procedures)

Not applicable.

Outcomes (applies only to therapeutic procedures)

Studies have shown no significant survival difference between those patients with malignant airway obstruction who received palliative chemotherapy (median survival, 8.4 months) and those who received treatment with laser, stent placement, or both, followed by chemotherapy (median survival, 8.2 months).

In a multicenter trial of 1058 patients in whom 1574 stents were placed (of which 698 were for malignant airway obstruction), stent migration occurred in 9.5 percent, granuloma formation was observed in 8.0 percent, and stent obstruction by mucus occurred in 4.0 percent. In another study of 125 silicone stents placed in sixty patients with malignant disease and thirty patients with benign tracheobronchial disease, migration was observed in 13 percent and granuloma formation in 6 percent.

The Wallstent is a self-expanding device made of cobalt alloy braided filaments that also has special features of outward radial force provided by its integral design and an optional cover that prevents growth of tumor and granulation tissue through the stent's thin wire mesh. In a report describing use of the Wallstent, stent-related obstructive granulation tissue was found in 11 percent of patients, and stent migration was not observed.

Ultraflex stents are self-expanding stents made of nitinol, an alloy with shape memory that deforms at low temperatures and regains its original shape at higher temperatures. In a study of fifty-four Ultraflex stents, immediate relief of dyspnea was achieved in 82 percent of patients, and stent migration was not observed.

In a study of long-term outcomes in patients with malignant or benign airway strictures who were treated with Wallstents and Ultraflex stents, a complication rate of 0.06 complications per patient-month was reported. Median follow-up was 42 days for patients with lung cancer, 329 days for lung transplant recipients, and 336 days for other benign conditions. The most common complications were infectious tracheobronchitis and obstructing granulomas that required interventions to restore airway patency. Tumor in-growth and stent fractures were also seen.

Alternative and/or additional procedures to consider

There are no additional or alternative procedures to consider.

Complications and their management

Most common complications are tumor in-growth, strent fracture, infectious tracheobroncitis, and obstructing granuloma. For obstruction granuloma and tumor in-growth, endoscopic removal by laser, cryotherapy, or argon plasma coagulation is required.

What’s the evidence?

Dasgupta, A, Dolmatch, BC, Abi-Saleh, WJ. "Self-expandable metallic airway stent insertion employing flexible bronchoscopy: preliminary results". Chest. vol. 114. 1998. pp. 106-109.

An early paper on the use of metal stents.

Diaz-Jimenez, JP, Farrero-Munoz, E, Martinez-Ballarín, JI. "Silicone stents in the management of obstructive tracheobronchial lesions: 2 year experience". J Bronchol. vol. 1. 1994. pp. 15-18.

A large series reporting on the use of the silicone stent.

Dumon, JF. "A dedicated tracheobronchial stent". Chest. vol. 97. 1990. pp. 328-332.

A description of the silicone stent.

Dumon, J, Cavaliere, S, Diaz-Jimenez, JP. "Seven experiences with the Dumon prosthesis". J Bronchol. vol. 31. 1996. pp. 6-10.

A description of the use of one particular airway prosthesis.

Gildea, TR, Murthy, SC, Sahoo, D. "Performance of a self-expanding silicone stent in palliation of benign airway conditions". Chest. vol. 130. 2006. pp. 1419-1423.

Report of the use of self-expanding silicone stent in which the failure rate was high.

Herth, F, Becker, HD, LoCicero, J. "Successful bronchoscopic placement of tracheobronchial stents without fluoroscopy". Chest. vol. 119. 2001. pp. 1910-1912.

A description of another method of stent placement.

Lee, P, Kupeli, E, Mehta, AC. "Airway stents". Clin Chest Med. vol. 1. 2010. pp. 141-50.

A good review showing when and how stents are used.

Mehta, AC, Dasgupta, A. "Airway stents". Clin Chest Med. vol. 20. 1999. pp. 139-151.

A useful review of stent placement.

Montgomery, WW. "T-tube tracheal stent". Arch Otolaryngol. vol. 82. 1965. pp. 320-32.

Description of a "classic" stent.

Miyazawa, T, Yamakido, M, Ikeda, S. "Implantation of ultraflex nitinol stents in malignant tracheobronchial stenoses". Chest. vol. 118. 2000. pp. 959-965.

Description of the use of a particular brand of stent.

Noppen, M, Meysman, M, Claes, I. "Screw-thread vs Dumon endoprosthesis in the management of tracheal stenosis". Chest. vol. 115. 1999. pp. 532-535.

Report on use of an alternative silicone stent.

Rafanan, AL, Mehta, AC. "Stenting of the tracheobronchial tree". Radiol Clin North Am. vol. 38. 2000. pp. 395-408.

A useful review of airway stents.

Saad, CP, Murthy, S, Krizmanich, G. "Self-expandable metallic airway stents and flexible bronchoscopy". Chest. vol. 124. 2003. pp. 1993-1999.

Description of the complications of stent placement.
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