Tracheal Collapse

Chapter 159

Tracheal Collapse

Tracheal collapse comprises a variety of conditions originally characterized as a degenerative disease of the cartilage rings in which hypocellularity and decreased glycosaminoglycan and calcium content lead to dynamic airway collapse during respiration. Other conditions include laxity of the dorsal tracheal membrane and malformed tracheal cartilage rings. Tracheal collapse is a disorder of predominantly small- and toy-breed dogs that can present with signs ranging from a mild, intermittent “honking” cough to severe respiratory distress from dynamic upper airway obstruction. Although more commonly seen in older patients, animals of all ages can be affected.

A careful history taking and physical examination are important to direct therapy and assist in determining prognosis. The history taking should be targeted to include any concurrent medical problems, the age of onset and duration of clinical signs, the progression of these signs, any factors that incite or worsen signs, the current frequency and severity of the signs, the effectiveness of any prior therapies in ameliorating cough or respiratory difficulty, and the occurrence of any episodes of cyanosis, syncope, or life-threatening respiratory distress. Further review of causes and diagnostic testing can be found in Chapter 144 of the previous edition of Current Veterinary Therapy.

General Treatment Considerations

Therapies are variable and depend on the severity of clinical signs, with some dogs requiring basic environmental modification and dietary therapy, others needing aggressive medical therapy, and the most severely affected requiring intervention. There is no definitive strategy that will work for all cases; for this reason, developing the final treatment strategy generally takes time and considerable trial and error with frequent client communication to achieve the most effective management. It is possible, however, to achieve a fair quality of life for most of these dogs as long as the appropriate expectation is explained to the client at the outset.

For those dogs with a primary history of cough, the most common complaint, environmental modification, weight loss, and medical therapy are the mainstays of therapy. Interventions such as intraluminal stenting or surgical prostheses should be reserved for dogs with life-threatening clinical signs or those for which medical therapy has failed. At what point such intervention is necessary is admittedly subjective. In most cases, after carefully evaluating a patient’s history, response to therapy, and current clinical status, the veterinarian and owner can determine when the time has arrived to consider an intervention. An exception to this rule is the emergent, intubated patient for which attempts at extubation have failed. An owner’s inability to administer medication is not a valid reason to perform one of these invasive procedures, because the majority of patients will still require medication following treatment. Placement of an intraluminal stent will initially stimulate the cough reflex; therefore, if the cough cannot be controlled medically, it is unlikely to improve with intervention. Furthermore, although intraluminal stenting and surgical prostheses can provide successful palliation for many dogs, both are associated with a moderate risk of complications. Therefore client education is critical, and the decision to proceed with tracheal intervention should be made only as a final option.

A detailed discussion of the diagnosis of tracheal collapse is beyond the scope of this chapter. In general the accepted diagnostic procedures include thoracic radiography, tracheal radiography, fluoroscopy, and endoscopy. Other primary or secondary respiratory disorders must be evaluated concurrently and addressed before more invasive therapies for tracheal collapse are implemented. For example, many dogs have concurrent bronchial collapse and others are affected by chronic bronchitis (see Chapter 160). Animals with concurrent cardiac or pulmonary disease often can benefit substantially from medical treatment of those conditions, so that more invasive tracheal collapse treatments can be avoided or postponed.

Clinical Syndromes of Tracheal Collapse

Conservative Therapy for Activity-Induced Cough

Many dogs with tracheal collapse have activity-induced coughing. Conservative therapy should be the first line of treatment for these patients. Weight loss, restricted exercise, and avoidance of secondhand smoke or inhaled irritants can reduce clinical signs. In addition, management of comorbidities such as cardiac disease or pulmonary disease can help reduce the incidence of respiratory crisis episodes. If the cough is infrequent, these modifications may be sufficient to control signs and avoid pharmacologic intervention or invasive procedures.

Medical therapy is critical to control signs in dogs with cough. Antitussive medications are the mainstay of therapy, with several options available. In the authors’ opinion, hydrocodone-based cough suppressants (Hycodan, Tussigon) are the most effective antitussives in dogs. A common misconception is that if the cough is not controlled on a standard dosage of hydrocodone, typically considered 0.25 mg/kg PO q6-8h, then this medication has failed. However, the authors have found that most dogs with tracheal collapse require higher dosages, and it is the rare dog whose cough cannot at least be improved with hydrocodone. As noted earlier, client education is critical, and the authors instruct clients that a gradual escalation of hydrocodone therapy may be required, with the dose typically increasing in 0.25-mg/kg increments every 5 to 7 days based on the dog’s response. The dose is gradually increased until either the cough is controlled or adverse effects of the hydrocodone manifest, usually excessive sedation or constipation. In the authors’ experience, hydrocodone dosages of 0.5 to 1 mg/kg PO q6-8h are typically effective; a dosage greater than 1.5 mg/kg PO q6-8h is rarely necessary. For small dogs, a liquid suspension of hydrocodone (often formulated to 1 mg/ml) is easier to use than tablets and makes incremental dose adjustments more feasible. When medical therapy is first initiated, a tapering course of prednisone is also begun to suppress tracheal irritation and inflammation in hopes of breaking the cycle of coughing that has already been initiated. The authors prescribe prednisone at a starting dosage of 0.5 to 2 mg/kg/day PO with a taper over 2 to 3 weeks. For some dogs, the addition of maintenance therapy with inhalant corticosteroids is beneficial to minimize cough. Fluticasone is the authors’ preferred inhaled corticosteroid, given at 110 µg/puff twice daily via a canine-specific spacing chamber and face mask.

The use of bronchodilators (e.g., theophylline, terbutaline) is often considered in dogs with tracheal collapse complicated by lower airway disease. In the authors’ experience, these medications provide minimal palliation of respiratory signs and, given their sympathomimetic properties, may exacerbate excitability and anxiety in these dogs, thereby inducing more adverse respiratory events. However, because many anecdotal reports suggest benefit from these medications, the veterinarian may consider a 2- to 4-week trial of extended-release theophylline at a conservative dosage (5 to 10 mg/kg q12h PO) to assess for a positive clinical response in an individual dog. If no improvement is noted by the client while the animal is receiving theophylline, continued use is not advisable. This medication may be most beneficial in those dogs with bronchial collapse demonstrated as an expiratory push upon exhalation. Inhaled albuterol (given before the fluticasone) may help through local delivery and may theoretically assist in achieving better lower airway steroid penetration.

Although bacterial infections have not been demonstrated to be common in tracheal collapse, it is conceivable that chronic lower airway disease combined with chronic tracheal collapse and subsequent failure of the mucociliary apparatus may impart increased susceptibility to tracheal infection or colonization. For this reason, a course of antibiotics (e.g., doxycycline or azithromycin) is often prescribed by the authors as part of a multimodality treatment regimen in hopes of controlling clinical signs and avoiding intervention if possible.

The final medical strategy for the patient with tracheal collapse is sedation before known episodes of excitement that may precipitate respiratory distress. The mild sedative effects of hydrocodone provide some benefit to minimize respiratory distress, but stressful events such as travel, visitors to the home, and so on, can lead to decompensation. To avoid this, acepromazine (0.5 to 2 mg/kg PO) may be prescribed as needed, to be given 30 to 45 minutes before an event known to lead to excitement and worsened respiratory signs. More recently, the authors and others have found use of the serotonin modulator trazodone at a dosage of 5 mg/kg q12h PO beneficial to minimize anxiety and excitement in dogs with tracheal collapse.

Management of Respiratory Distress

Another common clinical sign affecting a large proportion of dogs with tracheal collapse is respiratory distress secondary to an inadequate airway. There is often minimal history of coughing in these dogs, but respiratory signs may be severe, including cyanosis, syncope, or severe exercise intolerance. Medical therapy as outlined earlier can be considered in these dogs but is rarely sufficient in controlling signs in the long term. These dogs are the appropriate candidates for intervention—whether intraluminal stenting or surgical ring prostheses—because no medical therapy can restore tracheal rigidity and airway patency.

Recently, there has been a trend away from the use of ring prostheses with a higher proportion of dogs treated by intraluminal stenting. Unfortunately, there are no prospective studies directly comparing these two treatment strategies. The placement of extraluminal support rings around the trachea through an open cervical approach was associated with an overall success rate of 75% to 85% in reducing clinical signs in 90 dogs according to one report (Buback et al, 1996). This procedure is not without complications, however, because 5% of animals died perioperatively, 11% developed laryngeal paralysis from the surgery, 19% required permanent tracheostomies (half within 24 hours), and approximately 23% died of respiratory problems, with a median survival of 25 months. In addition, only 11% of the dogs in this study had intrathoracic tracheal collapse (all dogs had extrathoracic tracheal collapse). The authors of the retrospective study advised against the use of this technique in patients with intrathoracic tracheal collapse, because the resulting morbidity was unacceptably high.

The combination of surgical risk and the inability of the ring procedure to treat intrathoracic collapse adequately led to the evaluation of human-intended intraluminal tracheal stents for the treatment of affected dogs. A number of stents have been previously evaluated in the canine trachea, including both balloon-expandable (Palmaz) stents, and self-expanding stents (stainless steel, laser-cut nickel-titanium [nitinol], and knitted nitinol). Clinical improvement has been reported in 75% to 90% of animals treated with intraluminal stainless steel, self-expanding stents (Moritz et al, 2004), and long-term improvement was noted in 10 of 12 dogs treated with nitinol self-expanding metallic stents (Sura and Krahwinkel, 2008). Immediate complications were typically minor; late complications included stent shortening, development of excessive inflammatory tissue, progressive tracheal collapse, and stent fracture.

Neither surgery nor stenting is a cure for tracheal collapse. However, when used appropriately in the proper patients, either intervention can significantly improve the patient’s quality of life when medication alone is no longer adequate. Please see Chapter 145 of the previous edition of Current Veterinary Therapy for a complete description of the method for stent selection and the technique for placing intraluminal tracheal stents.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Tracheal Collapse

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