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Introduction

Relief of dyspnea or/and non-productive cough in patients with malignant or benign large airway obstruction is of primary importance. A variety of methods have been used, including dilatation, laser ablation, cryoablation, brachytherapy, photodynamic therapy, and silicone stent placement.

Tracheobronchial stents are used to relieve critical large airway obstruction due to severe extrinsic pressure, intraluminal spread of malignant disease or loss of normal cartilaginous support (tracheomalacia)^1-7. The principal complaints of patients with central airway stenosis are dyspnea and cough. In addition, stents may be placed temporarily in patients with benign stenosis to allow for adequate time to prepare for surgical management. Tracheobronchial stents are also indicated for permanent palliation in patients with benign stenosis who are medically unfit for surgical repair (e.g. due to poor respiratory reserve or heart failure).

The present study outlines the indications, technique and outcomes of tracheobronchial Dumon silicone stent placement in a series of patients with malignant and benign tracheobronchial stenosis.

Patients and methods

In the period 1999-2004, 57 silicone stents were inserted in the central airways of 50 patients. Irrespective of airway obstruction etiology (stenosis, tracheoesophageal fistula or tracheomalacia), tracheobroncheal stents were inserted under general anesthesia using alphentanyl and propofol, along with adequate local anesthesia (10% lidocaine spray). Patients were ventilated via assisted spontaneous breathing, without muscle relaxation. The Dumon Harrel Universal bronchoscope was used. This bronchoscope consists of two tubular parts joining together by screwing one part on the other. The upper part is always the same and includes ports for O₂ administration, insertion of suction catheter or laser probe, as well as a port for the insertion of a camera. The lower part includes tubes of varying diameter used during the procedure, depending on the diameter of the trachea or the bronchi (Figure 1).

Figure 1. Τhe Dumon Harell Universal bronchoscope and associated equipment.

In addition to clinical examination and plain chest radiographs, the assessment of the lesion prior to the procedure also included flexible fiberoptic bronchoscopy and spiral computed tomography of the trachea. In two cases, virtual bronchoscopy was also employed, which is a computed tomography technique that uses computerized data to reconstruct three-dimensional images of the tracheobronchial anatomy.

Initially, the location, diameter and length of the stenotic lesion were determined. Once a stent of appropriate length, diameter and configuration was chosen, it was attached to the delivery system. The stent was then threaded through the bronchoscope and pushed to the more distal point possible of the stenosis, where it was released by gradually pulling out the bronchoscope. The final positioning of the stent exactly in the stenotic segment was achieved by pulling the stent out with mild semicircular movements using a specially designed clamp.



Results

The age of the 50 patients who received tracheal stents ranged from 49 to 75 years. Of them, 30 (60%) patients had stenosis caused by malignancy (Table 1); 17 (34%) had benign stenosis (Table 2); and 3 (6%) patients presented tracheoesophageal fistula (Table 3). 6 (12%) patients required more than one stents (Table 4). In particular, two stents were placed in 5 (10%) patients and three stents in one (2%) patient. In 9 (18%) patients, laser ablation of the intraluminal mass projection was performed during the procedure prior to stent placement.



In total, 57 tracheobronchial silicone stents were placed, of which 24 (42%) were tracheal (T) stents, 26 (46%) carinal (Y) stents, and 7 (12%) bronchial (B) stents.

Forty-eight (96%) patients recovered immediately after the procedure. Of these 48 patients, 44 (90%) demonstrated immediate improvement in lung function as evidenced by arterial blood gas and oxygen saturation measurements before and after the procedure, and had an uneventful course after stent insertion Three (6%) patients who tolerated the procedure well, presented displacement of a straight tracheal stent (T). In 1 (2%) patient, granulation tissue had developed distally to the stent 6 months later.

Two (4%) patients required admission to the intensive care unit (ICU) immediately after the procedure. Of them, one patient had lung cancer with malignant carinal stenosis due to extrinsic compression, which had led to total atelectasis of the left lung preoperatively. The patient underwent dilatation and placement of a carinal (Y) stent. Due to the presence of copious bronchial secretions, tracheal intubation using fiberoptic bronchoscopy was necessary to facilitate bronchial toilet and suction. On day 4 after stent insertion, the patient was extubated and the lungs were fully expanded. The second patient had benign tracheal stenosis due to prolonged intubation. Having suffered an acute myocardial infarction 4 months before which resulted in an ejection fraction of 20%, the patient developed acute heart failure during recovery. Fiberoptic bronchoscopy was again used to intubate the patient, who was transferred to the ICU for the management of the acute heart failure, which eventually was successful.

Figure 2. a. Stent obstructed by dried secretions. b. Appearance of stent lumen after clearing dried secretions.

Of the three (6%) patients with stent migration, one had tracheomalacia resulting from total laryngectomy for the resection of laryngeal cancer and permanent tracheostomy for two years. This patient underwent repeat bronchoscopy and the stent was placed back to its place. The second patient had progressive dyspnea 9 months after the insertion of a straight stent. Bronchoscopy revealed that the stent was partially occluded by dried secretions due to continuation of smoking and negligence of the necessary humidification (Figure 2). The dried secretions were removed and mechanical intraluminal washing of the stent was performed, leaving the stent in place. One year later, the initial stent was replaced by a stent greater in diameter and length due to the development of tracheomalacia distal to the initial stent. The third patient with stent migration, underwent repeat bronchoscopy during which the stent was repositioned (Figures 3, 4).

Figure 3. Tracheal stenosis due to extrinsic compression before (a) and after stent insertion (b). Two silicone stents were required, a straight and a bifurcated (Y-shaped) one. The bifurcated stent is seen in the background of the picture.

Another patient developed progressive dyspnea 6 months after the insertion of a tracheal stent, caused by the formation of granulomas distally to the stent. Firstly, the stent was removed; the granulation tissue was then resected using diathermy and a bronchoscopic clamp; and the procedure was completed with the insertion of a new stent with the same dimensions to avoid the sequelae of a possible contamination of the initial stent.

Figure 4. Malignant tracheal stenosis before (a) and after the insertion of a straight Dumon stent (b). Multiple tracheal dilatations preceded stent insertion.

The results of the stenting procedure and patient acceptance have been excellent. None of the patients complained about pain or dyspnea. Only few reported awareness of the presence of a foreign body for a few days. To reduce the risk of infection, two measures deem necessary: (1) adequate sterilization of the stent; and (2) administration of appropriate antibiotic treatment for several days according to the results of susceptibility testing of the pathogens cultured in bronchial secretions, prior to stent placement.

Figure 5. Tracheobronchomalacia. Appearance of the carina before (a) and after stent insertion (b).

Discussion

Several types of stents are available, including: a) metallic (e.g. Palmaz); b) metallic expandable (e.g. Gianturco, Wallstent, Schneider); c) silicone (e.g. Dumon, Montgomery, Hood); and d) silicone covered metallic stents (e.g. Dynamic, Orlowski, Novastent, Ultraflex, Silmet).

The use of metallic stents in the management of tracheobronchial stenoses was first described in 1951 by Belsey⁸ and Bucher et al^9.

The first successful placement of a silicone stent in the large airways was described by Montgomery in 1965; he inserted a silicone T-shaped tube in the trachea. Since then, special silicone stents have been designed for insertion in the trachea, the bronchi or the carina, as described by Graziano et al in 19675. Indications for tracheobronchial stenting include:

1. Malignant stenosis of the trachea or the bronchi (extrinsic compression of the large airways) in patients with short life expectancy.
2. Failure of laser ablation or dilatation to improve a malignant tracheobronchial stenosis.
3. Malignant tracheobronchial stenosis in patients requiring radiation therapy.
4. Subglottic stenosis due to prolonged mechanical ventilation, in which the use of laser failed or is contraindicated.
5. Benign tracheal stenosis in patients medically unfit for a surgical repair.
6. Benign tracheal stenosis of inflammatory origin pending response to systemic therapy, or in preparation for operation.
7. Local or extensive tracheo-bronchomalacia (Figure 5).
8. Anastomotic stenosis after lung or heart-lung transplantation or tracheal surgery.³
9. Tracheo- or bronchoesophageal fistula (only silicone stents).
10. Incomplete laser resection of intraluminal mass.

The issue of the ideal stent has been, and still is under study. The ideal material would not be susceptible to infection, would not induce reaction to foreign body and would be relatively easy to insert. Metal, silicone, marlex or combinations of these materials have been used in various stents^11-14.

Currently, silicone stents and silicone covered metallic stents are most commonly used worldwide. Dumon stent is made of soft silicone and is available in various lengths, diameters and configurations (Figure 6).

Figure 6. The Dumon silicone stent.

To reduce the risk of stent migration, the outer surface of the stent has projections (barbs) that ensure fixation of the stent in the right position in the trachea or the bronchi. This leads to limited stent migration and reduced ischemia of the tracheal or bronchial wall.

These stents are invariably inserted through a rigid bronchoscope specially designed for this purpose and equipped with a stent delivery system. The bronchoscope initially dilates the stenotic segment and then is pulled out to insert the stent in the right position. Silicone stents are currently most widely used in Europe and North America. Essential advantages of silicone stents include their availability in a variety of lengths and diameters, as well as in a Y-shape configuration, which has not yet been feasible with metallic stents. Hence, they can be used to restore carinal pathology. In addition, they can be easily removed. Accordingly, they present a further comparative advantage, as they can be removed after 1-2 years of acting like a tracheal “splint”. It is worthy of note that in the comment of Naunheim on the work of Madden et al¹⁴, the non-removability of the metallic stents is particularly stressed, with special reference to the injury caused by the metallic ends to the respiratory epithelium, which should be considered in patients with benign stenosis in particular.

In large benign stenoses, the average time a stent stays in place is 1-2 years, whereas in malignant stenoses the respective time is four months, which equals the life expectancy of these patients. However, in cases of lowgrade malignancy, stents have been reported to remain in place for up to seven years⁶.

During the early post-insertion period, patients should be instructed to use inhalations of a normal saline spray, at an average of four times daily. The number of inhalations may be gradually reduced to finally reach a point of using saline inhalations only in the event of copious expectoration and low humidity.

Follow-up bronchoscopy to confirm satisfactory stent position is necessary and should be performed once or twice a year. Stents displaced due to migration should be either repositioned or removed. Acute respiratory distress indicates obstruction or migration, which is commonly associated with cough.

Progressive respiratory distress may be due to: a) granulation tissue formation; b) obstruction by secretions; and c) disease recurrence distally to the stent. In these cases, the stent should be removed; the tracheal or bronchial lumen should be opened up using diathermy or laser ablation; and the same stent or a greater one (in length, diameter) should be inserted to cover the neoplastic lesion. Halitosis suggests bacterial or fungal growth and should prompt stent replacement.

The Dumon stent can be easily removed using the endobronchial capture clamp for foreign body removal. The stent is slightly turned around to detach from the tracheal wall; its upper end is squashed and finally drawn toward the end of the rigid bronchoscope to be pulled out along with it. Once the stent has been removed, it is essential to remove excess tissue that has formed in the margins of the stent, such as debris and granulation tissue.

Conclusively, the insertion of silicone stents is a safe and effective technique for the management of extrinsic compression stenosis, be it benign or malignant in origin, which may extend to the level of the secondary carina¹¹.

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