Air Way Stents

2009

Airway stents Dr. T. Balasubramanian

Stenting of airway in time has saved a lot of lives. This eBook attempts to describe the various airway stents available, when to use them and how to use them. Complications of airway Stenting has also been dealt with in detail.

drtbalu www.drtbalu.co.in 1/1/2009

Air way stents By

Dr. T. Balasubramanian M.S. D.L.O

Introduction: Airway stenting involves stenting of both larynx and trachea. Stents could be solid or hollow, absorbable or non absorbable. Stenting is usually resorted to in order to prevent airway collapse or to stabilize the reconstructed airway.

History: The word stent is derived from in memory of Charles Stent a British Dentist who developed a material to create dental impressions. This moulding material which was initially used for dental impressions was later used to prevent grafted material from collapsing. In lay terms now the word stent could mean any structure that keeps the lumen of hollow organ patent and functioning. Montgomery in 1965 first introduced the still popular tracheal stenting tube, which was christened after him. It was this stent which revolutionized trachea bronchial surgery.

Indications of airway stents: 1. Can be used to stabilize reconstructed airway 2. It also helps in keeping the airway expanded after airway surgical procedure 3. Useful in managing a traumatized airway facilitating mucosal regeneration and prevention of airway stenosis 4. Can be used to stabilize cricoid plate after anterior / posterior cricoid split & grafting procedures. It also helps to keep the cartilage graft inserted. It also helps to counteract scar contracture. 5. Laryngeal web surgeries : Laryngeal keel stenting is resorted to after successful laryngeal web resection 6. Stenting of trachea may be resorted to in tracheal malignancies as a palliative measure 7. Useful in maintaining airway in primary tracheomalacia

Classification of airway stents: 1. 2. 3. 4.

Primary laryngeal stents Primary tracheal stents Bronchial stents A combination of laryngeal and tracheal stents

Laryngeal stenting: Is resorted to when stenosis is confined to larynx / subglottic area. In short term stenting the stent is left in place for a period of less than 6 weeks and in long term stenting the stent should be left in place for more than 6 weeks. Laryngeal Stenting is indicated in patients who have undergone resection of laryngeal lesions to prevent laryngeal web / stenosis formation. Short term stenting of larynx can be resorted to in order to stabilize grafts in place after laryngeal reconstruction, to keep the laryngeal mucosa apart in patients with laryngeal injury as a prophylaxis against stenosis. Long term stenting becomes necessary if long term stabilization becomes necessary when extensive tracheal segment resection and anastomosis have been performed. Laryngeal keel is the commonly used laryngeal stent. Stenting should not be resorted to in individuals who are medically unfit / allergic to stent material.

Tracheal Stenting: Is resorted to in patients who have undergone primary resection anastomosis for stenosis, stabilization of trachea in cases of primary tracheomalacia. It has been demonstrated that Stenting preserved and improved mucociliary function of laryngotracheal mucosa. Metallic wall stent is preferred for tracheal Stenting as this could promote normal mucosal regeneration. Metal wall stents are used for long term Stenting of trachea and Montgomery T tube is used for short term Stenting.

Fixation of stents: Stents can usually be fixed in situ by placement of stay sutures. T tubes can be stabilized in position without sutures because of their shape.

Laryngeal stents: Aboulker stent: This is the most common stent used to stabilize airway after laryngotracheal reconstruction in children. This stent was introduced by Aboulker in 1960. These stents are cigar shaped and is about 120 mms long available in different diameters. This stent is made

of Teflon which is highly polished. This polished Teflon stent minimizes mucosal irritation and granulation formation. If coated with Mitomycin – c before insertion this could minimize fibrosis also. This stent has been known to promote healing while keeping the reconstructed area stable. This laryngeal stent should be placed between true and false cords and sutured in place using large Prolene stitch tied externally to strap muscles. Multiple knots should be administered for later identification during removal. Aboulker stent can be used as short and long forms. Short forms can be anchored using Proline stitches where as the long form will have to be anchored additionally to the tracheotomy tube also as shown in the figure below

Long Aboulker stent seen anchored to Jackson’s tube.

Aboulker stents of various sizes

Montgomery laryngeal stent: This is a molded silicon prosthesis designed to confirm to the normal endolaryngeal surface. This stent is radio opaque and is firm enough to support the laryngeal mucosa. It is reasonably soft also to prevent pressure damage to the laryngeal mucosa. This stent is excellent in supporting intralaryngeal grafts (mucosal / skin). This stent is provided with two buttons which could be used to suture the stent in place. These buttons are placed over the skin and suture is passed through them to anchor the stent. These buttons facilitate easy post op removal of stent at a later date. This stent is ideal for prevention & treatment of laryngeal stenosis involving (midglottis, posterior glottis, subglottis and supraglottic singularly or in combination).

Montgomery laryngeal stent

Montgomery laryngeal keel: This umbrella shaped keel made of medical grade silicone. It comes in three sizes. It is available in clear and radio opaque versions. Its surface is smooth and non adherent. Indications:    

Repair of anterior glottis stenosis To prevent stenosis following hemilaryngectomy To maintain anterior commissure after laryngeal web resection Used to hold the laryngeal mucosa apart after laryngeal trauma

Laryngeal keel

Montgomery T tube: This silicone stent has a long central lumen and a smaller lumen projecting from the side of the stent at an angle of 75˚ / 90 ˚. The upper end of this stent should extend through the true cords up to the level of false vocal cords. The lower end of this stent should extend up to the level of carina. The side lumen should extend through the tracheostoma. This stent is useful after laryngotracheal reconstruction in adults. This stent may be unsuitable in children because crusting can cause acute airway obstruction needing immediate removal which may be difficult in a child. If this stent is used the side arm should be kept blocked most of the time to prevent crusting. A functioning nasal airway provides enough moisture to the inspired air and prevents crust formation. The patency of this stent should be ensured by frequent suctioning through the side portal.

Montgomery T tube

Indications:      

In tracheal stenosis, when the cervical and thoracic trachea cannot be repaired / as a substitute for the cervical trachea when it cannot be repaired To support the reconstructed cervical trachea Prior to reconstruction to maintain airway till inflammation subsides As a palliation in patients with unresectable tracheal tumors With segmental resection & anastomosis In patients with tracheal narrowing and who are not ideal candidates for surgery

Silastic sheets / (Swiss roll stents): This stent was popularized by Evans in 1977. This form of stent is useful during laryngotracheal reconstructions. This stent is commonly used in children. This is actually a thin Silastic sheet rolled and inserted into larynx and upper trachea. This stent is secured in place by sutures. This stent has a tendency to unroll and cause uniform increase in pressure over mucosa facilitating good healing.

Brick’s stent: This is an endotracheal tube made of PVC. This stent is used to stabilize airway following laryngotracheal reconstruction procedures. This can at most be used as a

short term stent as it is prone to cause granulation of airway mucosa if left in place for more than 4 weeks.

Silicone stents: This stent is commonly used in adults. This should be introduced only after dilating the larynx enough to place the stent. The dilatation should be at least 18mm for ideal placement of this stent. If dilatation could not cause sufficient enlargement of lumen then laser luminization should be performed using Co2 laser. This stent should be secured by placing stitches and exteriorizing the knot outside the skin. This stent should always be placed below the level of vocal cords because it can cause extensive vocal fold oedema if placed between the cords. This stent can be used for long term Stenting also.

Complications: 1. Vocal fold oedema 2. Stent migration 3. Recurrent stenosis after stent removal

Inflatable stents: Stents of this group has a small balloon attached to a port. This balloon can be inflated at intervals. This stent may be useful in the management of subglottic stenosis. The balloon should be expanded over a period of 3-6 weeks. Studies have shown that this stent causes very tissue irritation / reaction.

Tracheobronchial stents: These stents are used for Stenting trachea and bronchus hence can only be tubular in shape. There are two types of tracheobronchial stents i.e. Silicone and metal stents. Metal stents: Metal stents are easier to use in distal trachea & bronchi because they are made of metal mesh and will not obstruct distal bronchi. Metallic stents are coated with silicone in order to minimize tissue irritation (these are hybrid stents). Gianturco stents: This metal stent was originally developed to be a vascular stent. This is a stainless steel stent. This stent was introduced into the tracheobronchial tree from 1980. Since this stent had barbs over its walls they caused pin point damage to the tracheal mucosa. It is because of this problem of mucosal damage and high extrusion rates this stent has become obsolete.

Palmaz stent: This is also a steel stent. This stent has an expandable balloon and was devised for blood vessel / bile duct Stenting. This stent is of tubular mesh configuration. Its

length varies from 10 – 40 mm. A balloon of 6-10mm diameter fits inside the stent and can be manually dilated. When the balloon is inflated it does not cause continuous pressure over the tracheobronchial walls. This stent is ideal in children because of its small size. Indication:  

This stent is ideal for patients with primary tracheomalacia / bronchomalacia In patients with external compression of trachea/bronchi

Strecker stent: This is a metallic stent made of tantalum mesh. This is cylindrical in shape. It is very flexible when compressed or expanded. Usually it is about 2-4 cm long and can be expanded to about 8-11mm. This stent is very useful in tracheobronchial obstructions. Self expanding metallic stents: These stents have memory that allows it to return to normal shape after compression for placement in the airway. These stents usually expand spontaneously but sometimes need to the inflated. Stents belonging to this group are: 1. Gianturco-Z 2. Wall stent 3. Nitinol Wall stent: This is a tubular metal stent composed of 15-20 braided steel filaments of (100µm) thickness. The filaments are arranged in a criss cross fashion to form a cylindrical mesh. This stent is best to maintain tortuous airways. This stent can be positioned using a rigid / flexible bronchoscope. Diameter of this stent varies from 6-25mm and length ranges from 2-7 cms. It must be ensured that the diameter of the stent is at least 2mm wider than the measured diameter of the normal airway. The stent usually shortens by 20% after deployment; hence correction for it should be applied. Main advantage of this stent is that small openings can be cut on its surface thereby facilitating good bronchial ventilation.

Nitinol stent: This stent is also known as ultraflex stent. This stent is unique among metal stents in that it changes its shape according to temperature. This feature is known as Marmen effect. This stent gets distorted at low temperatures (martensitic state) and reverts back to original shape when reheated (austenitic state). This stent is heated and made into a helical shape and is then cooled for deployment. When inserted this stent on exposure to higher body temperature coils back to its original shape. The same effect can be achieved by applying current of 3 amperes and 3 volts to the stent. It increases the temperature of the stent to 40˚c thus reverting it back to fully expanded state. Recently they have coated this stent with Teflon there by reducing tissue reaction to it. Silicone stents:

1. 2. 3. 4. 5.

Dumon stent Reynder stent Dynamic stent Polyflex Novastent

Dumon stent: This stent was introduced by Dumon in 1980. This stent can easily be inserted via a bronchoscope. It is cylindrical in shape and is made of medical grade silicone. Studs are placed over the wall of the stent at regular interval to prevent its migration. It is available in varying widths and lengths. Once in position it can be adjusted through bronchoscope. This is currently the most widely used air way stent. This stent has a thick wall and is unsuitable for pediatric use. Thin walled Dumon stents are currently being introduced. Dumon – Y stent: This stent has been most recently introduced. This can be introduced from trachea into both bronchi. It is softer than most “Y” stents. It is difficult to insert than the normal Dumon stent.

Dumon Y stent Reynder stent: This is cylindrical silicone prosthesis. This is more rigid than other silicone prosthesis. A special introducer supplied with the stent should be used to insert it through the bronchoscope. Dynamic stent: These are anatomically shaped bifurcated silicone stents. They have a flexible posterior membrane resembling the normal tracheal posterior wall. This membrane can bulge inwards during coughing making it more physiological (hence the name dynamic stent). The usual problems of Stenting like retained secretions; are very rare

when this stent is used. This stent is really useful in managing stenosis of long segments of trachea. Dynamic stents are available in 3 sizes, and can be cut to desired size. Polyflex stent: This is a self expandable stent made of polyester wire mesh within layers of silicone. Novastent: This is another silicone stent made of thin sheet of medical grade silicone. It contains a small metallic hoop of Nitinol alloy hence it is a hybrid stent. Bioabsorbable tracheal stents: Bioabsorbable stents are being developed and animal studies of the same have been encouraging.

Check list before stent insertion: 1. 2. 3. 4. 5.

Is Stenting really necessary? Will the patient benefit from Stenting? Will insertion of stent prevent surgical procedure? What is the ideal stent for the said condition? What are the diameter / length of the stent needed?

In cases of benign strictures a short removable stent is preferable as Stenting is necessary for only a short duration. In patients with tracheomalacia / laryngomalacia a long standing stent which will not be extruded easily is desirable (metal / hybrid stents). In patient with malignant stricture of airway, a wire mesh stent is not useful as the tumor tissue can grow through the mesh. Polymer stents / covered metal stents are desirable in this scenario. Airway dilatation is a must before introduction of stent. If dilatation is not possible using dilators then laser luminization should be resorted to. All patients who have undergone Stenting of air way should be provided with a stent pass. This pass should contain details regarding the type of stent inserted, exact location of insertion, whether endotracheal intubation is possible, if so what size tube that could be used should be clearly stated in the pass.

Complication of Stenting: Migration: This is common when polymer stents are used. Usually these stents are held in position by the pressure exerted by the stent with that of the airway mucosa. Tubular silicone stents are usually held in position by placing sutures. These stents are usually provided with studs, rings and protuberance that will hold it in position. Migration is common in patients with malignant strictures who have undergone irradiation. Irradiation usually causes some amount of tumor shrinkage predisposing to migration.

Mucostasis: In normal conditions about 5 ml of mucous is produced in the airway. This secretion is easily cleared by the mucociliary system of the airway. If the patient is a smoker the quality of mucous secretion is thick and adheres to the stent. Metal stents cause more Mucostasis and the secretions should be coughed out by the patient. This is where dynamic stents play an important role as they don’t impede mucociliary clearance. Regular use of mist inhaler will moisten the mucous facilitating better clearance. Excessive mucous secretion can be reduced by use of antibiotics and steroid inhalers. Stent obstruction: Stents can be obstructed due to failure of mucous clearance. Dry mucous can cause crusts obstructing the stent. Regular suction clearance of mucous secretions will help. The inspired air can be kept moist by regular use of mist inhalers. Stent obstruction is uncommon in Montgomery T tubes as the horizontal limb can be kept closed and the patient can normally breathe through the nasal airway. In patients with malignant strictures, the malignant tissue may grow through the small holes of metal stent blocking the airway. In patients with malignant strictures it is always better to use a silicone stent. In patients with metal stents, it may irritate the airway mucosa causing it to granulate. This granulation tissue may grow through the pores of the metal stent causing it to obstruct. Mechanical stent failure: Air way stents are under constant pressure. Persistent coughing may cause fracture of the stent causing failure. This is more common in metal stents because of metal fatigue.