Tracheal collapse is a progressive, degenerative disease of the cartilaginous rings of predominantly older small and toy-breed dogs (Pomeranian, miniature and toy poodle, Yorkshire Terrier, Chihuahua, Pug) in which hypocellularity, decreased glycosaminoglycan, and calcium contents lead to dynamic airway collapse during respiration. Affected animals present with signs ranging from a mild, intermittent “honking” cough and exercise intolerance to severe respiratory distress from dynamic upper airway obstruction. Any or all portions of the trachea and bronchi can be affected. Respiration contributes to the collapse. On inspiration the pull of air into the lungs creates negative pressure in the lumen of the cervical trachea and positive pressure opening the tracheal rings of the intra-thoracic trachea and bronchi. During exhalation, the opposite occurs, so the intra-thoracic pressure to push air out results in compression of the intra-thoracic components, while the air moving out serves to open the extra-thoracic trachea in the cervical region.
Various combinations of anti-inflammatories, anti-tussives, sedatives/tranquilizers, and/or brochodilators are typically effective in alleviating the initial respiratory problems associated with tracheal collapse. In addition, weight loss, restricted exercise, and removal of second hand smoke or inhaled allergens can further palliate clinical signs. Careful regular monitoring of co-morbidities such as cardiac disease or pulmonary disease may help reduce the incidence of respiratory crisis episodes. Those patients that have failed aggressive medical and environmental management and have had other potential causes of respiratory disease either treated or ruled out become candidates for surgical treatment. An owner’s inability to administer medication is not a valid reason to perform surgery as the majority of patients will still require medication following treatment.
Tracheal collapse is suspected with an appropriate signalment, history and eliciting coughing reflexes with simple digital palpation of the trachea. Radiographs and fluoroscopy of the lateral cervical and thoracic trachea in an unanesthetized patient during inspiration and expiration can be diagnostic for tracheal collapse. Radiographs are diagnostic in approximately 60% of patients with moderate to severe tracheal collapse. Special attention should be paid to evaluating the mainstem bronchi because animals with mainstem bronchial collapse are unlikely to benefit from surgical repair of their collapsing cervical trachea. Presently, there is no clinically used method to stent collapsing mainstem bronchi; however, a recent publication investigated intraluminal stents for mainstem bronchial collapse and concluded that such a technique might be useful in affected dogs. In addition to evaluating the trachea on radiographs, thoracic radiographs should also be evaluated for cardiomegaly and pulmonary disease.
Evaluation of laryngeal function under a light plane of anesthesia should also be performed to rule out laryngeal paralysis or laryngeal collapse. Laryngeal paresis, paralysis, or collapse is present in approximately 30% of dogs with tracheal collapse. Unfortunately, not all cases can be diagnosed easily, and it may be necessary to elicit a cough while obtaining radiographs to demonstrate tracheal collapse. Endoscopy/tracheoscopy is an excellent technique to evaluate the trachea and bronchi and can be used to grade the degree of collapse. It is also recommended as a procedure to evaluate the trachea prior to surgery in all dogs, regardless of radiographic findings. Cytology and culture of the airway should be obtained to determine if a bacterial component is involved. Recurrent bacterial tracheitis can occur with severe tracheal collapse.
Grade I - tracheal membrane is slightly pendulous, cartilage maintains normal AC@ shape, lumen reduced approximately 25%
Grade II - tracheal membrane widened and pendulous, cartilage is partially flattened, lumen reduced approximately 50%
Grade III - tracheal membrane is almost in contact with dorsal trachea, cartilage is nearly flat, lumen is reduced approximately 75%
Grade IV - tracheal membrane is lying on dorsal cartilage, cartilage is flattened and may invert, lumen is essentially obliterated
The result of tracheal collapse is an extremely small cross-sectional area of functional tracheal lumen and high airway resistance. This increase in resistance along with chronic hypoxia causes increased right ventricular work and can lead to enlargement (hypertrophy) of the right side of the heart.
Extra-luminal prosthesis techniques were the most widely used technique until 10 years ago. Both ring and spiral prosthesis has been described for this use. Ring prostheses are made by either making individual C-shaped rings or continuous spiral prosthesis. The prosthesis is applied taking great care not to interfere with the vascular or nerve supply of the larynx or trachea. The most common complications associated with extra luminal prosthesis are placement. Complications with this technique include intra-luminal hemorrhage because of suture penetration, peritracheal swelling/inflammation, damage to the recurrent laryngeal nerve resulting in laryngeal paralysis and tracheal necrosis and slough from ischemia if the blood supply to the trachea is severely compromised. If paralysis occurs, surgery (laryngeal tieback) is usually necessary for survival. Coughing usually improves several weeks after surgery; however, this procedure does not usually make these dogs normal.
Due to the relatively high morbidity associated with surgery and the inability to successfully treat intra-thoracic tracheal collapse, the use of minimally invasive intra-luminal stents has been investigated. A number of stents have been evaluated in the canine trachea, including both balloon-expandable (Palmaz) and self-expanding (Stainless steel, Laser-cut nitinol, Knitted nitinol) stents. The vast superior flexibility makes the use of self-expanding metallic stents particularly appealing for tracheal use in dogs. Clinical improvement rates in 75%-90% of animals treated with self-expanding, intra-luminal stainless steel stents have been reported.
Intra-luminal tracheal stents are best reserved for dogs with tracheal collapse that are not good candidates for extra-luminal prosthesis and have failed medical therapy. They can be placed in dogs with intra thoracic tracheal collapse. The main contraindication to their use is in dogs with collapse of the main stem bronchus. They offer the advantages of minimally invasive deployment, short postoperative convalescence, and rapid restoration of airway lumen. When properly sized and appropriately deployed, the short term improvement in respiratory function is truly remarkable. Postoperative coughing is never totally alleviated since the stent interferes with the mucociliary clearance of sputum and predisposes the patient to lower airway infection. Unfortunately, because of their location, they are also subject to severe cycling and bending forces. Consequently, the stent is prone to kinking and the tracheal wall is prone to granuloma formation at the rostral and caudal extents of the stent. Additionally, these stents are very difficult to remove after deployment and adjustment of a broken unit is not possible. Fortunately, fractured stents lend themselves to repair by telescoping of a new stent through the kinked or fractured region. Owners must be advised that tracheal stents should be deployed as late in the animals’ life as possible since few patients live more than 2-3 years without developing one of the previously mentioned significant complications. Unfortunately, medical therapy, surgery, or stenting are not cures for tracheal collapse. When used appropriately in the proper patients, however, stenting can significantly improve the patient’s quality of life when medications alone are no longer adequate.
There remains some debate with regards to the use of intra-luminal stents in patients with bronchial collapse in addition to tracheal collapse. Stenting of mainstem bronchi is not currently recommended as secondary and tertiary bronchi will continue to collapse, and therefore the benefit of mainstem bronchial stenting will be minimal and temporary. Certain patients will benefit from tracheal stenting even when concurrent mainstem bronchial collapse is present. Once again, patient evaluation and selection is key in determining the value of stenting in these potential candidates. Tracheal collapse can lead to dyspnea, coughing, or both. Bronchial collapse will usually manifest as a cough, expiratory dyspnea, or both. When both tracheal and bronchial collapse is present, the results following tracheal stent placement becomes less predictable. If dyspnea is the only clinical sign and intra-thoracic tracheal collapse is present, a tracheal stent can help relieve the dynamic obstruction. If the dog’s primary problem is coughing, then it becomes difficult to determine if the coughing is secondary to the tracheal collapse or bronchial collapse. In the cases in which stents are placed, the bronchial collapse will inevitably continue to progress and continued coughing will be present. Continued coughing will cause repeated cycling of the stent and may increase the risk of subsequent fracture of the implant or predispose to the formation of excessive granulation tissue.
As mentioned previously, placement of intra-luminal stents is not a cure. Stenting is a palliative procedure, and the vast majority of patients will require continued medical therapy for a good long-term outcome.
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