Theresa W. Fossum, DVM, MS, PhD, Diplomate ACVS
Tracheal collapse is a commonly recognized disease of toy and miniature-breed dogs (e.g., Toy Poodles, Yorkshire Terriers, Pomeranians, Maltese, Chihuahuas) associated with tracheal cartilage flaccidity and flattening. Either sex may be affected and most animals are middle-aged when clinical signs are noted; however, animals as young as one year of age may be diagnosed with this condition. The etiology of tracheal collapse is unknown and probably multifactorial, but may include genetic and nutritional factors, neurologic abnormalities, and cartilage matrix degeneration. In affected animals, the cartilages usually collapse in a dorsoventral direction, with the cervical trachea collapsing during inspiration and the thoracic trachea collapsing during expiration.
With tracheal collapse, clinical signs often progress with age and include abnormal respiratory noise, dyspnea, exercise intolerance, cyanosis, and syncope. Clinical signs are more severe in obese animals. Respiratory noises include wheezing, hacking, coughing, and stridulous breathing, although some dogs do not make abnormal respiratory noises. The cough may be productive or nonproductive but is classically a "goose honk" cough. Coughing often becomes cyclic and paroxysmal and gagging is common. Signs may be elicited or exacerbated by tracheal infections or tracheal compression. Second-hand smoke may also precipitate clinical signs.
Differential diagnoses that should be considered include other causes of chronic coughing or respiratory distress such as brachycephalic syndrome, tonsillitis, laryngeal collapse, laryngeal paralysis or paresis, bronchitis, tracheobronchitis, allergies, heartworm disease, pulmonary disease, chronic mitral valvular disease, hypoplastic trachea, tracheal stenosis, and tracheal neoplasia.
Tracheal hypoplasia is a congenital form of tracheal stenosis that occurs when tracheal cartilages are abnormally small and abnormally shaped. The tracheal cartilages are circular (the ends appose or overlap), rather than C-shaped, causing tracheal rigidity. The dorsal tracheal membrane is narrow or absent. Tracheal hypoplasia (Table 1.) primarily affects brachycephalic breeds, especially English bulldogs. Affected dogs may have other congenital abnormalities such as stenotic nares, elongated soft palate, and megaesophagus. They may have continuous respiratory distress, coughing, and recurrent tracheitis, or may have intermittent signs that are mild or moderate. This condition can typically be diagnosed on radiographs and must be differentiated from tracheal collapse. Treatment consists of symptomatic medical therapy (i.e., antibiotics, cough suppressants) and correction of other airway obstructions (e.g., resection of nares, palate, saccules); however, because the entire length of the trachea is involved, surgical correction is not feasible. Traumatic stenosis may occur following trauma or surgery. If only a segment of the trachea is involved, the narrowed area may be treated by balloon dilation or tracheal resection and anastomosis may be performed.
Table 1. Radiographic Diagnosis Of Hypoplastic Tracheas
Ratio of tracheal lumen diameter at the thoracic inlet to the thoracic inlet diameter (TD/TI) < 0.20
Ratio of tracheal lumen diameter at the midpoint between the thoracic inlet and carina to width of the 3rd rib (TT/3R) < 3.0
Palpation of the trachea may reveal flaccid tracheal cartilages with prominent lateral borders and may elicit paroxysmal coughing. A soft end-expiratory noise may be auscultated in some dogs with intrathoracic tracheal collapse and probably represents the walls of the trachea snapping together during expiration. Abnormal heart sounds may be associated with concurrent cardiac disease. Electrocardiography may reveal sinus arrhythmia or evidence of cor- pulmonale or left ventricular enlargement.
The first step in diagnosing tracheal collapse is usually to perform inspiratory and expiratory lateral radiographs of the neck and thorax. Because the collapse is dynamic (the cervical trachea collapses on inspiration and the thoracic trachea on expiration), both inspiratory and expiratory films should be taken to evaluate the entire trachea. Radiographs are diagnostic in approximately 60% of patients with moderate to severe tracheal collapse. Fluoroscopy, though seldom available in veterinary practices, facilitates evaluation of the dynamic movement of the trachea and mainstem bronchi through all phases of respiration. 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.
If tracheal collapse is suspected, but radiographs were non-diagnostic, tracheoscopy should be performed. It is also recommended as a procedure to evaluate the trachea prior to surgery in all dogs, irregardless of radiographic findings. Prior to performing tracheoscopy, laryngoscopy should be performed to rule out associated conditions causing upper airway disease. Laryngeal paresis, paralysis, or collapse is present in approximately 30% of dogs with tracheal collapse. Laryngoscopy must be performed under light anesthesia. During tracheoscopy, tracheal conformation should be evaluated as the scope is withdrawn to determine the location and severity of the collapse. The entire trachea is usually collapsed; however, one area of the trachea is often more severely affected and is used for classification purposes. Grade I tracheal collapse is a 25% reduction in lumen diameter with the trachealis muscle being slightly pendulous and the cartilages maintaining a somewhat circular shape (Table 2.). Grade II collapse is a 50% reduction in lumen diameter with the trachealis muscle stretched and pendulous and the cartilages beginning to flatten. Grade III collapse is defined as a 75% reduction in lumen diameter with the trachealis more stretched and pendulous and the cartilages nearly flattened. In grade IV collapse the lumen is essentially obliterated; tracheal cartilages are completely flattened and may invert to contact the trachealis muscle. Tracheal cultures and brushings taken during tracheoscopy are useful in selecting antibiotics. Positive tracheobronchial cultures are found in more than 50% of animals with tracheal collapse.
Table-2. Classification of Tracheal Collapse
25% reduction in lumen diameter
Trachealis muscle is slightly pendulous
Cartilages are more circular than flattened
50% reduction in lumen diameter
Trachealis muscle somewhat stretched and pendulous
Cartilages mildly flattened
75% reduction in lumen diameter
Trachealis muscle is stretched and pendulous
Cartilages nearly flat
Tracheal lumen is obliterated
Medical therapy is recommended for all animals with mild clinical signs and those with less than 50% collapse. Medical therapy for dogs with tracheal collapse (Table 3.) includes antitussives, antibiotics, bronchodilators, and/or corticosteroids. Sedation with acepromazine (0.05 to 0.2 mg/kg [maximum 1 mg] intravenously, intramuscularly, or subcutaneously, TID) and/or diazepam (0.2 mg/kg intravenously BID) and supplemental oxygen may be required in severely dyspneic patients. Weight reduction should be instituted for obese patients. Exercise restriction is recommended. Affected dogs should be maintained in an environment free of smoke and other respiratory irritants or allergens. Response to medical therapy is usually transient and the disease typically progresses.
Table 3. Medical Therapy of Tracheal Collapse
Butorphanol tartrate (Torbutrol®)-0.5-1.0 mg/kg; PO; BID to TID
Hydrocodone bitartrate (Hycodan®) 0.2 mg/kg; PO; TID to QID
Ampicillin-22 mg/kg; IV, IM, SC, PO; TID
Cefazolin (Ancef®, Kefzol®) 20 mg/kg; IV, IM; TID
Clindamycin (Antirobe®)-11 mg/kg; PO; BID
Enrofloxacin (Baytril®)-5-10.0 mg/kg; PO or IM; BID
Dogs-11 mg/kg; PO, IM, IV; TID
Cats-5 mg/kg; PO; BID
Oxtriphylline elixir (Choledyl®)-15 mg/kg; PO; TID
Dexamethasone (Azium®) 0.2-0.5 mg/kg; IV, IM, SC; BID ; up to 2 mg/kg
For emergency treatment
Prednisone-1-2 mg/kg; PO; SID to BID
Surgery is recommended for all dogs with moderate to severe clinical signs, a 50% or greater reduction of the tracheal lumen (without significant mainstem bronchial collapse; see above), and those refractory to medical therapy. Dogs presenting with laryngeal paralysis or collapse, generalized cardiomegaly, and chronic pulmonary disease are poor surgical candidates. Coughing and dyspnea caused by laryngeal, pulmonary, or cardiac disease are unlikely to improve without appropriate therapy. Respiratory distress and death may occur in animals with severe laryngeal dysfunction or bronchopulmonary disease.
The goal of surgery is to support the tracheal cartilages and trachealis muscle, while preserving as much of the segmental blood and nerve supply to the trachea as possible. Many techniques have been described. Currently, the only techniques that meet this goal are placement of individual rings or modified spiral ring prostheses. Generally only the cervical trachea and most proximal portion of the thoracic trachea are supported, even when cervical and thoracic tracheal collapse are present. Readers are referred to surgical textbooks for descriptions of tracheoplasty using individual ring prostheses. Patients with concurrent laryngeal paralysis or laryngeal collapse may also require arytenoid lateralization or permanent tracheostomy, respectively.
The main complication of tracheoplasty is laryngeal paralysis. The segmental blood and nerve supply to the trachea travels in the lateral pedicles on each side of the trachea. The left recurrent laryngeal nerve is located in the lateral pedicle; the right is sometimes located within the carotid sheath.