Collapsing Trachea


This is some information from D.J. Krahwinkel, Jr., DVM, MS
Diplomate, ACVS, ACVA, ACVECC
Professor of Surgery at the University of Tenn.

Collapsing trachea is a progressive disease usually found in small and toy breed dogs such as Yorkshire terriers, poodles, and Pomeranians. Etiology is unknown; for some reason, the tracheal rings lose their organic matrix, and the cartilages are unable to maintain their C shape. Initially the dorsal longitudinal membrane becomes floppy and is pulled into the airway during breathing. The ends of the tracheal cartilage become farther apart and the C shape of the ring eventually flattens, completely occluding the airway, particularly at the thoracic inlet. The mainstem bronchi can also be affected. Other conditions associated with tracheal collapse include lung parenchymal disease, chronic heart disease, and obesity. Tracheal collapse can be exacerbated by pressure of an enlarged left atrium on the left mainstem bronchus in patients with chronic mitral valve disease.

Clinical signs usually start with a cough that can be harsh, dry, or sound like a goose honk. Physical examination findings may be nonspecific. In some dogs, the cough can be initiated with tracheal palpation. In dogs that are stressed or anxious, tachypnea, hyperthermia, and cyanosis may be present. Increased inspiratory and expiratory sounds or cardiac murmur may be present on auscultation. On abdominal palpation, many animals have enlarged livers. Many dogs will have aerobic growth on culture of the tracheal secretions (obtained during brush cytology) but do not consistently have cytologic evidence of tracheal inflammation or infection.

Diagnosis of tracheal collapse is based on radiographs, fluoroscopy, and especially endoscopy. The trachea is usually collapsed in a dorsoventral direction and can be mildly to severely affected. Radiography underestimates the extent of collapse. Endoscopy is particularly useful for evaluating extent of the tracheal collapse and determining whether bronchial collapse is also present. Some animals may have concurrent laryngeal paralysis, so laryngeal function should be examined under light anesthesia before intubation for endoscopy or surgery.

Treatment

Treatment depends on the severity of clinical signs and tracheal collapse and whether any concurrent conditions can be improved. Animals that are distressed or cyanotic should be administered oxygen and sedatives as soon as possible. Antitussive agents, such as hydrocodone syrup or butorphanol, are administered to reduce coughing. Injectable or oral steroids are given to reduce inflammation and edema. Bronchodilators (aminophylline, theophylline) improve mucociliary clearance and decrease small airway spasm. Obese animals are placed on a weight reduction diet; in some animals, weight reduction alone can resolve signs. Neck collars are removed, and harnesses are used in animals that are leash walked. Up to 70% of animals have improvement in clinical signs with medical management alone.

Intraluminal Stents: Intraluminal stenting is a minimally invasive technique for preventing tracheal collapse. It is usually performed under fluoroscopic or endoscopic guidance with the animal maintained on injectable anesthesia. To determine stent size, the maximal diameter of the trachea is measured on radiographs taken under anesthesia during manual inflation of the trachea and lungs, and the length of the trachea is determined on radiographs and with endoscopy. A stent is chosen that will expand to 1-2 mm greater than maximal tracheal diameter and that preferably will support the entire trachea, or at least bridge trachea beyond the collapsed region. Current intraluminal stents are made of a nickel-titanium alloy ("nitinol") that has a high radial force to resist dynamic compression, plus excellent flexibility to help the stent retain its shape. They are self-expanding, with a repositionable/reconstrainable delivery system. This allows a partially deployed stent to be retracted back into the delivery system and repositioned during fluoroscopic or endoscopic evaluation. The catheter containing the stent is placed into the trachea under endoscopic guidance, and the stent is gradually released, starting at the tracheal bifurcation and extending cranially. To reduce coughing, the stent should not extent into the region of the cricoid cartilage or into a mainstem bronchus.

Dogs that undergo intraluminal stent placement are always prone to coughing after the procedure: after all, there is a foreign body in their airway. Eventually the stent becomes covered with tracheal epithelium, but that epithelium may not have normal structure or function, and also the bronchi may continue to collapse. All dogs are placed on cough suppressants and glucocorticoids after the procedure, and many may need sedation and antibiotics for two weeks. Glucocorticoids are continued for one month and then are gradually decreased. If the cough reoccurs after the glucocorticoid dose or cough suppressant is decreased, the animal is placed back on a higher or more frequent dose. The cough cycle must be broken immediately in these dogs, even if it means keeping the dogs heavily sedated for days. Coughing can result in breakage of the stent. Because stents cause coughing, they are not used in dogs in which clinical signs are limited to coughing.

Intraluminal stents are expensive and are therefore usually placed in animals that cannot be managed medically. Mortality rates after stent placement are 17% within the first two months; overall, about 31% of dogs die of respiratory problems 5 days to 2.5 years after placement. Dogs can live for more than 4 years after stent placement. Besides continued coughing, complications include stent fracture (>20%), stent migration, tracheal collapse cranial or caudal to the stent, exuberant granulation tissue formation, rectal prolapse, and perineal hernia.

Extraluminal Tracheal Ring Prostheses: The trachea can also be supported by surgical placement of extraluminal (peritracheal), C-shaped, synthetic rings above, below, and at the level of collapse. Prostheses are secured to the trachea with interrupted sutures. A cervical approach is used for animals with cervical or thoracic inlet collapse; thoracotomy is required for intrathoracic distal tracheal collapse. Extraluminal prosthesis placement requires dissection of one or both recurrent laryngeal nerves from the trachea, which increases the risk of postoperative laryngeal paralysis. Some animals may require laryngeal tieback after surgery. Some surgeons automatically perform unilateral arytenoid lateralization in order to avoid this complication. Because of the potential complications of extraluminal prosthesis placement and the invasive nature of the procedure, intraluminal stenting is used more commonly.


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