Tracheal collapse and tracheal stent placement
Tracheal collapse is a disease common in many small breed dogs where the cartilages of the trachea weaken over time. As they weaken, the negative pressure created when the pet inhales is too much for the trachea to maintain its shape so it collapses. This narrows the pet's airway and makes it difficult to bring air in. The decreased airflow causes hypoxia and leads to dyspnea and coughing. This is a chronic progressive disease that is manageable, but not curable
This consists of controlling coughing and preventing increased oxygen demand by the body. Weight loss, exercise restriction, heat restriction, maintaining patient calm, anti-inflammatories, and antitussives are considered the mainstay of therapy. Antibiotics are occasionally necessary since these patients are more prone to secondary bacterial infections.
At some point, medical therapy will fail due to disease progression and decreased oxygenation ability. The videos below are good examples of what happens to the trachea in dogs with tracheal collapse as they breathe.
Once medical therapy fails, surgical therapy is recommended. The two main forms of treating tracheal collapse include placement of tracheal rings (in case of cervical tracheal collapse) and tracheal stenting. Since this disease is progressive, dogs with cervical tracheal collapse will eventually develop intrathoracic tracheal collapse.
The tracheal stent is placed within the lumen (opening of the trachea) and it forces it to remain open. For this procedure, we anesthetize a patient and guide a nitinol (nickel-titanium alloy) stent into the trachea. Since tracheal collapse may begin in some areas and eventually spread to affect the entire trachea, our goal is to stent as much of the trachea as possible. The stents expand once released into the trachea and provide additional support to prevent collapse.
Tracheal stenting has become more popular over the years. However, there are important considerations prior to recommending stenting.
In order to place a tracheal stent correctly, it is very important to measure the collapse appropriately. Oversizing the stent can lead to stent fracture while undersizing can lead to migration and chronic infections (due to space between stent and trachea). Sizing is also important because it is ideal to stent as much of the trachea as possible since the tracheal collapse will likely progress over time.
We recommend intubating the patient with the cuff inflated near the cricopharyngeal apparatus and putting 20 cm of H20 pressure to distend the trachea as much as possible. Even though this is the traditional measuring method, this method can still lead to undersizing when compared to CT. We recommend using a stent approximately 20% wider than the measurement of the trachea.
In order to appropriately measure the diameter of the trachea, we also recommend using a measuring catheter that is placed within the esophagus. This will allow the most accurate measurement. Digital radiographs have calipers built-in, but we have found at least a 10% difference when compared to a measuring catheter. It is important to measure the trachea in many areas and use a shortening chart to determine the likely length of the stent once deployed. When picking a stent, the length is determined if the stent is open to the maximum diameter. Since we use stents that are 20% bigger than the measurement of the trachea and since the trachea has different diameters depending on the location, having an idea of the average diameter is important. This will help prevent picking a stent that is either too short or too long.
It is also important to have many different stents in stock since most dogs with tracheal collapse are unstable by the time a stent is needed. Therefore, anesthetizing to measure and then place the stent at a different time is less than ideal.
While guidelines for stent placement have been developed, experience is very important since stent placement is not considered an exact science.
The stent should be placed under fluoroscopic guidance to best evaluate where to start deployment. The stent is placed through the endotracheal tube, which is pulled as the stent is placed. We recommend using a Y-piece to allow oxygen delivery at the time of stent placement. Slight forward force is made during deployment to help the stent open to its maximal capacity.
We feel that it is important to inspect the trachea with a scope prior to stent placement as well as post-stent placement. Post-stent placement evaluation is key to make sure that there are no spaces between the stent and the trachea (make sure there is good apposition). Some clinicians also advocate doing a bronchoalveolar wash in these patients since most of them will have a secondary bacterial infection.
Monitoring post-tracheal stent placement
It is important to take chest radiographs post-stent placement to document placement. Additionally, it is important to retake chest radiographs routinely to make sure the stent is intact.
Controlling coughing is key post-stent placement because coughing can also put pressure on the stent and it may contribute to stent fracture.
Possible complications of stent placement and general expectations
Possible complications of this procedure include fracture of the stent, excessive formation of granulation tissue around the stent, and stent migration (very rare). With the recent advances in stent technology and an increased knowledge of proper stent size and placement, these complications are significantly less common than they previously were, but they can still potentially occur. Unfortunately stent placement will not "cure" the disease. The majority of patients who receive a stent will have reduced severity of clinical signs, but they will not go away completely. The stent itself can cause some degree of irritation within the trachea, so we expect that some coughing will continue. Less commonly, the coughing may get worse (if it were present). However, the stent will help prevent any acute life threatening crises from the trachea collapsing. Following placement the pet may still need to be on medication for the rest of their life depending on how they do. The stent will also not address a main stem bronchi collapse.
Fortunately, these are uncommon complications. The stent will prevent the pet from going into respiratory collapse. However, it will not prevent coughing. Some patients with tracheal stent have improved coughing, while others have worsening of the coughing post-stent placement.