Tracheal collapse frustrating; minimally invasive tehniques promising

Most commonly, tracheal collapse occurs in middle-aged to old dogs including Yorkshire terriers, Pugs, Chihuahuas, Pomeranians, Maltese, as well as Miniature and Toy Poodles.

Affected dogs might present with a variety of clinical signs ranging from coughing and exercise intolerance to episodes of cyanosis and collapse. The stress of a physical examination can exacerbate clinical signs.

Definitive diagnosis can best be obtained with the use of fluoroscopy while the patient is awake. Generally, the unsedated patient is held in lateral recumbency, and the cervical trachea is massaged to induce coughing. Using fluoroscopy, the location and extent of the collapse can be documented. Some veterinarians advocate the use of endoscopy in combination with fluoroscopy.

Photo 1: A lateral thoracic radiograph documenting tracheal narrowing extending from the mid-cervical area to the mainstem bronchi in a toy breed dog.

Endoscopy allows visualization of the internal surface of the larynx and trachea but might not accurately define the extent of the collapse. Another means of diagnosing this disease is radiography (Photo 1); however, radiography is not a dynamic diagnostic tool, and affected patients may be missed, or the extent of collapse may be underestimated. In fact, in one study, radiographs were normal in 20 percent of cases. Alternatively, a tentative diagnosis can be made and conservative treatment initiated based on signalment and clinical signs.

The pathophysiology of the collapsing trachea is not completely understood. It has been suggested that dorsoventral flattening of the c-shaped tracheal rings is secondary to decreased chondroitin sulfate and calcium and/or hypocellular cartilage.

Photo 2: The stent delivery system can be placed easily through an endotracheal tube. The metallic markers on the delivery system can be seen easily with fluoroscopy and aid in deployment.

The weakened tracheal cartilage predisposes the rings to collapse during the pressure changes of normal ventilation. Also, redundancy of the dorsal membrane may be a contributing factor.

Medical considerations

Traditional therapy for collapsing trachea consists of medical management, including cough suppressants, anti-inflammatory medications, bronchodilators and tranquilizers. The main goals of medical management include depressing the cough, reducing tracheal inflammation and reducing excessive excitation. Cough suppressants, such as hydrocodone, lomotil and butorphanol, can be used as frequently as every six hours. The most common side effects of these medications include constipation, depression and lethargy. The anti-inflammatory medications most commonly used are corticosteroids, such as prednisone and dexamethasone. Steroids, such as fluticasone (Flovent) can be used as inhaled medication with the help of a pediatric spacer. Steroids are useful for treating tracheitis and laryngitis that occur secondary to coughing and tracheal collapse. The side effects of the corticosteroids can include polyuria, polydypsia, polyphagia and gastrointestinal irritation. These systemic effects are reduced when administered as inhaled medication. Bronchodilators are used to open the lower airways to increase gas exchange. Bronchodilators, such as theophylline and aminophylline, can also have an anti-inflammatory effect and can help reduce inflammation that occurs in the trachea. The side effects of bronchodilators might include vomiting, diarrhea, excitement and insomnia. Tranquilizers are often used to prevent excessive excitation. In most cases, we recommend only starting with a single drug, then adding additional therapies one at a time so that the patient's clinical response to each therapy can be evaluated.

Photo 3: Fluoroscopic view of the stent delivery system within the trachea prior to deployment.

When the clinical signs are not controllable by medical management alone, additional methods of therapy should be considered. Reported surgical options for collapsing trachea include plication of the dorsal tracheal membrane, placement of extraluminal polypropylene prosthetics and placement of intraluminal stents. With extraluminal techniques, spiral or c-shaped polypropylene prosthetics are sutured along the exterior of the extrathoracic collapsing portion of the trachea.

Complications include tracheal necrosis and laryngeal paralysis. In one study, 16 percent of patients had a permanent tracheostomy performed within two weeks of extraluminal c-shaped stent placement, and 6 percent died from complications associated with laryngeal paralysis in the immediate post-operative period. In addition, these extraluminal techniques are not recommended for intrathoracic tracheal collapse.

More recently, placement of intraluminal self-expanding nitinol tracheal stents has become an available, efficient, effective and minimally invasive method of preventing tracheal collapse. Stent size is selected by measuring the diameter of the trachea and length of the collapse using fluoroscopy. Patients are generally sedated with acepromazine and butorphanol to decrease anxiety and coughing and then placed under general anesthesia. The delivery system containing the self-expanding stent (Photo 2) is placed through an endotracheal tube to the desired location within the trachea (Photo 3). As the stent is unsheathed, placement can be visualized in real-time using fluoroscopy. Prior to final deployment, the expanded stent can be reconstrained and repositioned, if necessary. Proper placement is essential for optimal results (Photo 4). Stent placement adjacent to the carina could result in occlusion of the mainstem bronchi and placement adjacent to the larynx could result in laryngospasms and excessive post-operative coughing. The intraluminal stents are made of woven nitinol wire. Nitinol is an alloy of nickel and titanium and is a soft metal with excellent memory. It can be deformed (i.e. compressed into the delivery system) and then has the ability to return (i.e. expand) to its original shape.

Photo 4: A lateral thoracic radiograph after placement of an intraluminal tracheal stent.

Migration and fracture concerns

Post-operative complications include migration and fracture of the stents, collapse of the trachea adjacent to the stents, excessive formation of granulation tissue and decreased mucociliary function. Migration of tracheal stents can be life-threatening if the mainstem bronchi became occluded. If migration does not occlude the carina but is displaced from the site of collapse, additional stents may need to be deployed in the trachea. Tracheal resection and anastomosis has been reported as a successful treatment for a fractured tracheal stent. Additional stents may be placed for collapse proximal to the initial stent, as long as the additional stent does not interfere with the larynx. Excessive granulation tissue may be responsive to corticosteroids.

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After stent placement, most dogs show an immediate improvement of clinical signs. Patients may have a transient dry cough secondary to irritation that can be treated by continuing corticosteroids and cough-suppressant therapy. Over time, the corticosteroids and cough suppressants are tapered and discontinued. Some dogs will have mild residual cough and some form of medical therapy may be needed to control and prevent excessive coughing. The reported mortality rate compares favorably to surgical options. Tracheal collapse is a frustrating problem to treat in dogs. In the past, extraluminal prostheses placed surgically have been the standard of care with various success rates and a high rate of perioperative morbidity.

Intraluminal stents have become the preferred method of surgical treatment in the authors' hospital. Overall, intraluminal nitinol tracheal stents are proving to be an efficient, effective and minimally invasive means of treating tracheal collapse when medical management has failed.

Carl Sammarco, BVSc, MRCVS, Dipl. ACVIM (cardiology) joined Red Bank Veterinary Hospital, Tinton Falls, N.J. in 2001. He previously served as a lecturer/assistant clinical professor at the University of Pennsylvania, where he completed a residency in cardiology in 1994 .

Garrett J. Davis, DVM, Dipl. ACVS, earned his veterinary degree from Cornell University, completed an internship at Red Bank Veterinary Hospital and completed a residency in surgery at the University of Pennsylvania. He re-joined Red Bank Veterinary Hospital in 2002.

Tara Britt graduated from the University of Pennsylvania School of Veterinary Medicine in 2002. She completed a rotating internship in small animal medicine and surgery at Red Bank Veterinary Hospital and is current a third-year resident in small animal surgery at the hospital.