Author: Isidoro Ricardo
Pulmonologist, Bronchoscopist, Chief of Respiratory Endoscopic Department. Hospital Enrique Tornú. Buenos Aires. Argentina
Tracheobronchial prostheses are utilized to treat obstruction of the great airway in benign conditions and to alleviate the effects of obstruction caused by neoplastic pulmonary disease.
In the last 20 years a large variety of stents have been used for this purpose until in 1990, Dumon published the results of his experience with a new prosthesis model in silicone. Since then, it has been the most widely used stent in the world (1-2-3-4-5-6-11-12).
The treatments carried out mostly require a recanalization procedure or “reconstruction” of the tracheal or bronchial clearance, often followed by the insertion of a prosthesis that ensures the support of the airway. The use of stents made out of silicone is also widely disseminated in our environment. Largely due to the long experience and long existing casuistry and, to a large extent, because it is a safe device and easy to apply and remove.
Method and Material
Silicone prostheses made of polysiloxane have been used, which have shown great tolerance, as a result of their elastic properties (7-10). The dimensions of the stent were determined by performing a fibrobronchoscopic examination prior to the interventional procedure. In this way the possible measures that will be required for their insertion were estimated. The prostheses, in turn, were available in progressive calibers from 5mm, and in variable lengths. On certain occasions, the stent underwent modifications consisting of adapting the length and angle of termination of the bronchial branches. This applies to the “Y” prosthesis, in the particular cases in which it was necessary to maintain ventilation of the right upper lobe, when it originated in a short bronchus source.
The ends of the prosthesis should be of soft termination, in order to achieve continuity with the bronchial mucosa without causing the appearance of inflammatory phenomena.
The airway unblocking procedures were performed with a high frequency electrocautery (12). All of them under general anesthesia, monitoring of the inspired fraction of O2 and exhaled carbon dioxide. Even so, no risk of combustion was possible because the ventilation was carried out with compressed air. In the benign stenosis, mechanical dilatation was performed (8), with or without a complementary resection with electrocautery.
The prosthesis to be inserted is lubricated with lidocaine gel, folded on its axial axis and inserted inside the prosthesis’ charger, through the mouthpiece provided for this purpose. Thus the assembly is introduced through the rigid bronchoscope that will be in the appropriate position to release the stent inside the area treated by the stenosis. The complete expansion requires, in some cases, maneuvers to complete the opening of the stent, with a forceps with toothed valves, of the crocodile type.
Deformations in the implanted stent were not taken into account when they did not affect more than 20% of their circumference. The recomposition of the circular light was always spontaneous in these cases, requiring for it, a term comprised between 48 hours and 7 days.
The tracheobronchial Y prostheses were implanted with a forceps capable of mounting it on the outside, with both bronchial branches folded. This was introduced through the glottis, visualized with an orotracheal intubation laryngoscope. This function can be fulfilled very well by the Storz clamp for dynamic stenting and was used in 3 cases. Other forms of Y prosthesis implantation are possible and perhaps simpler, depending on the experience of each operator.
For the extraction of the stent, it is taken by its proximal edge with the crocodile forceps, with sufficient firmness. A rotation movement produces the collapse of the stent, with reduction of its diameters and separation of the tracheobronchial mucosa. When the forceps are pulled, the same is extracted together with the bronchoscope. The same procedure is useful for removing the “Y” prosthesis.
Between March 15, 1999 and the 15 of the same month of the year 2002, 60 silicone prostheses were utilized to treat 50 patients, with benign or malignant lesions involving trachea, carina, bronchi sources or intermediate, separately or in combination; and that produced partial or total occlusion of the airway.
The group of patients consisted of 23 women and 27 men, ranging from 14 years old to 85 years old, with a general average of 50.2 years.
Twenty-two of them had benign tracheal stenosis, with an exceptional case of single involvement of left-sided bronchus, also of the benign stenosis type.
All cases, with the exception of one, had a clear history of tracheal intubation, sometimes as brief as 72 hours.
The histological diagnoses of the malignant conditions, in a total of 28 cases, were: 12 adenocarcinomas, 6 squamous, 3 carcinomas of small cells, 2 undifferentiated and other two could only be identified as carcinoma.
One case corresponded to the invasion of the tracheal clearance by thyroid carcinoma. A bronchial obstruction with carinal invasion was also treated by the metastasis of clear cell renal carcinoma. Finally, an infrequent loss of the tracheal cartilaginous support took place due to actinic necrosis of this organ, in a patient who underwent radiant treatment for squamous cell carcinoma of the right upper lobe.
Type of prosthesis and its location
We used 12 tracheo-bronchial “Y” stents, all of them measuring 15mm in tracheal diameter and 12mm in each of the bronchial branches. The lengths of them, as well as those of their tracheal portion, were adjusted, in each case, to the affected distance in the airway, bearing in mind that no stent should be longer than necessary. In this way, the necessary section of the prosthesis was always followed by the abrasion of its edges in order to eliminate sharp angles in the material, which could affect the mucosa. This is how the sectioned branch acquires the original conformation.
The rest of the prostheses were 21 bronchial and 27 tracheal that, being provided in the necessary measures, never needed to be shortened.
The greater number of stents than of patients is explained because some of them required more than one during their treatment, due to local progression of the neoplastic disease, from the source bronchus to the carina or towards the trachea. Other stents were replaced at 12 months due to hypersecretion and embedding.
A single case with adenocarcinoma was treated with two prostheses; one in the right source bronchus and another implanted four months later in the distal trachea, due to disease progression.
The bronchial prosthesis was inserted in the left bronchus, in 12 cases, in the right in 9 and in the intermediate bronchus in 2.
The description of the complications will be brief, since they were comparatively low (6).
Hypersecretion was the most frequent manifestation and occurred in 5 cases (8.3%). The patients performed nebulizations with saline solution during 4-hour intervals, without resolving the increase in the amount of secretions.
Then aspirations were made with a fiber optic bronchoscope, with special interest in removing secretions that could be stuck to the internal wall of the stent. They become consistent due to the dehydration that results from the increase of air flow velocity in the prosthesis, with a smaller caliber than the airway itself in the same path. When its removal was not satisfactory, the prosthesis was removed and replaced.
In one case (1.6%), colonization of the stent by candida albicans was demonstrated one year after insertion and was also replaced.
The development of granuloma in the free edge of a tracheal stent implanted as a consequence of a benign stenosis was observed in only one case (1.6%).
Regarding migration, it only occurred in 3 cases (5%), corresponding entirely to benign stenosis in which the mucosal surface, much more regular than in neoplastic infiltration, reduces the possibilities of stent fixation.
Compression of the prosthesis due to tumor growth was not observed in any case. This is easily explained by the pressure support possibilities offered by the wall of the prosthesis, which is between 800 and 1000 grams per square centimeter. Neither occlusion of the stent was observed due to growth of the neoplasm.
A 50-year-old woman consulted for hemoptotic expectoration. His chest x-ray was normal. The broncho-fiberscopic examination showed the presence of a formation that occluded 90% of the left source bronchus, settling 1 cm from the carinal edge. The lesion corresponded to an adenocarcinoma and was resected with electrocautery. A 12 x 35 stent was implanted at that level.
One year later the prosthesis presented incrustation of whitish secretions with firm adherence to the internal wall. His study showed the presence of Candida Albicans. The stent, which showed little useful section for ventilation, was removed and replaced.
Fourteen months later, fixed secretions to the wall of the prosthesis were found and the stent replaced again, although the cultures were negative.
The following year, an expiratory wheeze was audible in the center of the chest; an endoscopic examination was indicated, with suspected subocclusion of the stent. The study allowed determining that the light of the prosthesis was normal; however, the progression of the disease caused intramural infiltration of the contralateral source bronchus wall, with a marked reduction in the light that caused wheezing. The edge of the carina was distorted and the removal of the left source bronchus stent was indicated for replacement by Y-carino bronchial prosthesis.
At the moment, the survival of the patient has exceeded 40 months.
A 45-year-old woman was referred to the service for atelectasis of the left lung. Eight years before admission, she had undergone left nephrectomy due to clear cell carcinoma. The same histological diagnosis was obtained after the examination of the biopsy specimen from the formation that totally occluded the light from the left source bronchus, in the vicinity of the carina.
No prosthesis was implanted until 10 months later, when significant local recurrence of the tumor was found, and submucosal miliary nodules in the carina slopes. A Y-stent was used, which had to be removed within a few days due to an incoercible cough, and replaced by a 13 x 35 bronchial prosthesis, which was implanted in such a way that its proximal end exceeded the edge of the carina.
New tumor recurrences were presented with a distal bronchial location, occluding lingula and superior lobe, which were treated with electrocautery through the fiberscope channel that was introduced through the stent, without it being necessary to remove it to vaporize the lesion. Successive treatment sessions were carried out until his death, 24 months after his first admission to the hospital.
A 71-year-old man was admitted to the intensive care unit for severe inspiratory difficulty, which required orotracheal intubation, without mechanical ventilation.
The patient was a carrier of an epidermoid carcinoma of the right upper lobe that, being considered in stage IIIB, received radiant treatment consisting of 6000 centigray on a field of 11.5 x 12 cm on the thorax.
The tracheal tube was removed and an endoscopic examination revealed the complete loss of the cartilaginous support of the intrathoracic trachea, with exposure of the rings. Image 2a
Inspiration was followed by incomplete collapse of the wall and many of the ends of the rings were “free” in the light. Purulent secretions lined a large part of the mucosa, whose biopsy indicated tissue necrosis.
A 16 x 70 millimeter silicone stent was inserted. It expanded so quickly that it was considered necessary to replace it with another 17 x 70 mm. The destruction of the tracheal rings or their separation from the fibroelastic sheath makes the trachea “complacent”, and a stent can thus expand comfortably (9), anyway the exposure of the cartilaginous arches resulted in an excellent fixation of the Stent in them. The maneuver allowed to recover the tracheal clearance and to keep the patient with spontaneous breathing. Image 2b
The usefulness of a stent to maintain patency of the airway seems beyond doubt.
The recurrence of benign stenosis, after the recanalization treatment by any endoscopic method is variable, and its immediate recurrence is avoided by the prosthesis. On the other hand, tracheal or bronchial resection and de-obstruction, followed by radiant treatment or chemotherapy may be sufficient in some cases, and the application of a stent immediately after recanalization could be questioned. However, the absence of reports about prosthetic obstruction due to proliferation of neoplastic tissue, make early use a safe way to maintain ventilation through and save a second future intervention to implant the prosthesis.
Although in all these cases it is accepted that its indication has a palliative purpose and is closely linked to the quality of life, especially in the case of a carino-bronchial stent, long survivals such as those we have presented can be found in many published series (2-3-11).
The use of two prostheses to understand affected areas such as bronchus source and distal trachea, when the contralateral source and bronchus remain intact, was preferred to the use of a “Y” Stent. The reason is that the entire length of the stent should be considered as a “foreign body” that exceeds that necessary to cover the condition being treated. As such, the dependent effects such as interference in ciliary sweep, excess stiffness, reduction of light, and greater impact of secretions, to mention just a few, should be taken into account. Therefore, the shorter the stent required is, the better.
Once again, the advantages already widely known for the great experience accumulated in the use of silicone prosthesis, will be reduced its drawbacks.
First of all, it will be mentioned the one that may have been least mentioned so far: the relatively scarce available light, taking into account that the wall of the prosthesis occupies between 33 and 36% of the total area of the stent section (*), or what is the same, in a silicone prosthesis only 2/3 of its diameter will be destined for air passage, and what is worse, the passage of secretions through it. This is related to the frequent retention of these secretions.
As counterpart of the high wall / light ratio, it is the same wall capable of tolerating between 800 and 1000 grams, -difference depending on the different models available-, per square centimeter of its surface without reaching the breaking point of its resistance to compression (**).
This translates in practice into a high tolerance to extrinsic pressures, which is reflected in the lack of reports of treated cases in which the prosthesis has lost its functionality due to excessive compression deformation on its walls and loss of light.
A low frequency of migration of the prostheses was presented in this series, after being implanted in benign tracheal stenosis. This frequency would be even lower if a case in which the prosthesis displacement possibilities were as many as those in which the stent was inserted in a lower position than it was actually necessary is excluded from the list. This raises a new topic of discussion about how to establish the exact length of affected tracheal mucosa after the dilatation maneuvers have been performed.
Indeed, at the beginning of the procedure, a fair impression of the lesioned characteristics can be obtained, as well as the ring in which they begin. As the procedure progresses, the initial determinations become inaccurate and this may result in an implant at a level that does not fully protect the affected area or choose an excessively long stent.
The widest possible prosthesis has always been chosen to be applied in the light achieved with the recanalization maneuvers, and this fact is directly responsible for the low frequency of migration of the stent. Using smaller diameter prosthesis is commonly tempting. After its release in the airway, its complete expansion is immediate and the task seems complete. A migration in these cases is possible.
The choice of a larger diameter stent promises a laborious expansion within the trachea. It can, at times, be so folded as to adopt a half-moon shape or worse, in “omega”, occupying all the tracheal light, leaving the impression of “occluded airway”. Even so ventilation through it will be possible. The use of inflatable balloons in order to expand the stent has not been satisfactory in our experience; since the balloon will spontaneously settle into the angle of the prosthesis that is folded into a horseshoe. The manual expansion, with a crocodile clip, will be very laborious but will be rewarded by a good fixation of the Stent.
As an orientation, when we have achieved a tracheal lumen so that a 12.4 mm external diameter bronchoscope can be introduced, we use a Stent of 13 or 14 millimeters; and when it has been dilated until it is possible to introduce an external 14.4mm bronchoscope, a Stent 15, or better 16mm, will be chosen.
(*), (**) Author’s determinations.
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