Silicone Stents

Inspired by the Montgomery T tube, J. F. Dumon in Marseille developed an original tracheobronchial silicone stent in 1987.

The Dumon stent® does not require tracheostomy for deployment.

Its external surface is covered by silicone studs which serve a dual purpose ; avoiding migration of the stent and distributing the stent’s pressure along small sections of mucosa thereby preserving blood flow to the area.

These are made from transparent silicone, which permits a view in transparency of the bronchial wall.

Radio-opaque silicone leads to a loss of transparency.

On a normal x-ray, a rectilinear zone in the tracheobronchial tree shows the position of the stent.

On CT scan, the stent is clearly visible.



These tubular stents are available in various sizes.

The tracheal stents are generally 50 to 60 mm long (maximum 110 mm), and 14 to 16 mm in diameter (maximum 18 mm).

Bronchial stents are manufactured with diameters ranging from 10 to 12 mm and lengths between 20 to 40 mm.

The flexibility of the stent is also important. A stent does not need to be particularly rigid to withstand the pressure exerted by a tumor. A flexible stent is better tolerated than a rigid one. However, the stenosis absolutely must be calibrated with a rigid tube prior to placing the stent. If the stent takes on an oval shape through primary compression, it will return to a round shape within 48 hours. Additional tumor growth has never resulted in compression of a stent that is already in place. However, the tumor can continue to develop above or below the stent. This is not local but circular compression. Unlike metal stent in a bronchus, no secondary compression is possible with a silicone stent.

Y stents designed to treat tumors extending to the carina are available with 15-16 mm tacheal limb diameters, and 12-13 mm main stem bronchial limb diameters.

The lengths of the tracheal and bronchial limbs are variable, reaching up to 110 mm for the trachea, and 50 mm for the main stem bronchi.

The right main stem limb may be fenestrated in order to facilitate right upper lobe ventilation.



Indications







The principal indication for airway stenting is extrinsic compression of the airway. In our experience, tracheal stenosis is the most common indication, followed by right main stem stenosis, and left main stem stenosis. Y stent placement is reserved for tumors extending to the carina.







Tracheal stenosis is the second main indication.

There are few other indications : bronchial fistula, tracheobronchomalacia…



Choice of the diameter and the lenght

The choice of stent depends largely upon careful measurements performed at the time of bronchoscopy.

The diameter of the stent will depend on the external diameter of the bronchoscope used (yellow tube 16/15, red tube 14/13/12), while the desired stent length is measured by retracting the bronchoscope or telescope along the entire length of the stenosis.

The stents must be perfectly fit to the tracheobronchial tree. To avoid complications, the shortest and widest possible stent must be used. Therefore, stenoses must always be calibrated prior to stent placement.



Width (in adults) :
 For the trachea, stent must not be less than 14 mm in width ; the ideal width is 16 mm for men and 15 mm for women (for people of European descent).
 For the main bronchi, the ideal width is 13 mm, with a minimum of 12 mm.

Length : Stents should not be too long. The ideal stent completely covers the lesion and extends no more than ½ cm beyond the lesion on each side.



Placement

 

Placement is performed using a tracheal or bronchial rigid tube.

The stent is lubricated with silicone and loaded into a stent applicator.

The applicator is the inserted through the bronchoscope and the stent is pushed out into the trachea or the bronchus.

Adjusting the stent is made by grasping the upper rim of the prosthesis ith foreign body forceps.



Patented Efer-Dumon applicator.

On the left, two kind of loaders, the small for short tracheal or bronchial stent, the longer, for long Y stent or long and large straight stent.

On the right two size of applicators.

Applicator and loaders are color coded in function of the size of the stents.



Placement of a Y stent

This film shows the placement of a Y stent during a live procedure (duration : 15 mn 30 s)

Surveillance



Airway stents demand careful maintenance and adequate surveillance. Aerosol therapy on a daily basis is mandatory. We generally ask the patient to use a nebulizer three times a day. We recommend pneumatic nebulizers rather than ultrasound. This treatment seeks to maintain adequate humidification of the airway and facilitate clearance of secretions with coughing (many patients are initially afraid to cough). A follow-up visit is scheduled one week after the procedure in order to document proper compliance with all recommendations. Surveillance endoscopy is not necessary for at least one year following stent deployment unless respiratory symptoms are present (cough, dyspnea, or respiratory distress). Cigarette smoking should be avoided, otherwise nicotine deposits can accumulate on the stent as seen in the following endoscopy image.



Stent related complications



Complications associated with stent placement are uncommon and rarely life-threatening. Three serious complications are worth mentioning ; stent obstruction, migration, and granulomatous inflammation. All three may present with similar symptoms, including ; respiratory distress, intractable coughing, and/or trouble clearing secretions. Emergent fiberoptic bronchoscopy should be planned any time a serious complication is suspected. In such cases, it is best to proceed with anesthesia consultation and consider hospitalization. Rigid bronchoscopy might be necessary in case stent removal or replacement are indicated.



Stent removal and/or replacement



Most stents are temporary solutions to transient airway stenosis. This is always the case with benign indications, especially tracheal stenosis. In case the stenosis is malignant, silicone stents may be left in place as definitive palliative therapy or replaced as needed depending on the patient’s evolution. Silicone stents can be removed at all times (in contrast to metallic stents), even after prolonged periods of time. Removal of a silicone stent requires grasping the stent with the rigid bronchoscopic forceps and turning it 360 ° in order to release the studs. The stent is then partially retracted into the bronchoscope and the entire ensemble is then removed from the airway. On occasion, the scissors are used to cut long stents which have been in place for years, in order to facilitate their removal.