Trachea

Introduction

The normal trachea is a dynamic organ composed of multiple hyaline cartilaginous rings, joined together laterally by fibroelastic annular ligaments, and across the tips of the cartilaginous rings dorsally by the tracheal membrane consisting of the trachealis muscle covered medially by ciliated epithelial mucosa. The fibroelastic annular ligaments allow for tracheal movement in any direction, whereas the trachealis muscle allows for expansion and contraction of the circumference and thus the diameter of the trachea and the volume of air that can move along the airway. Classic tracheal collapse occurs in a dorsoventral direction and results in patient symptoms varying in degree of severity from mild cough to total respiratory collapse. The canine patient is usually a middle-aged toy breed, but the age may vary, in my experience, from less than 1 year to 16 years of age.

Pathophysiology

The cause of tracheal collapse is unknown, but it is generally thought to be a congenitally predisposed, probably inherited, condition. Respiratory allergies and irritants (particularly tobacco smoke), obesity, chronic infections, trauma from collars, and endotracheal tube placement from general anesthesia have been reported to exacerbate the clinical signs. Lack of adequate innervation to the trachealis muscle is considered to be a possible cause. In a few cases, Dallman demonstrated an irregular hypocellular condition of the cartilage rings with less calcium and chondroitin sulfate present than normal. In some cases, the tracheal cartilage is softer than normal, with considerable loss of rigidity. However, occasionally the cartilage is more rigid than normal, resulting in difficulty in recontouring the cartilage during prosthetic ring placement. The cartilage rings may also be shorter than normal, especially at the thoracic inlet.

With disease chronicity, the ends of the tracheal rings become progressively further apart (Figure 26-1), allowing the tracheal membrane to sag into the tracheal lumen. Resonant vibration of the redundant tracheal membrane results in the classic honking cough. Increased negative pressure within the tracheal lumen during inspiration collapses the cervical trachea further and may balloon the thoracic trachea. Expiration results in collapse of the thoracic trachea and ballooning of the cervical trachea. Narrowing of the entire airway results in either event, especially on inhalation.

Tracheal collapse may extend into the mainstem bronchi, especially the left bronchus. Bronchial collapse may be accentuated because of compression by an enlarged left atrium. Heart enlargement, especially right ventricular hypertrophy, secondary to chronic airway disease is common. Tracheal mucosal erosion or metaplasia may be seen as a result of chronic inflammation as well as from alveolar emphysema and mineralization.
 

Lateral collapse of the trachea or ventral collapse with minimal widening of the dorsal membrane associated with loss of cartilage rigidity is seen infrequently. Collapse caused by pressure from external masses is rare. Laryngeal function may be less than optimal.

Recently, the not infrequent occurrence of collapsed tracheas in miniature horses suggests to the author that there may be an association with the gene/s responsible for “dwarfism”/miniaturization, and bears further study.

Diagnosis

A presumptive diagnosis is often made on the presentation of a toy breed dog exhibiting a honking cough, with a history of chronic respiratory infections. Yorkshire Terriers, toy poodles, Pomeranians, Chihuahuas, and Maltese are most commonly affected. The condition has been seen rarely in mixed or larger breeds of dogs, cats, and miniature horses. The disorder has no sex predilection.

Most patients, probably those with a grade I collapse, respond to medical therapy consisting of antibiotics, cough suppressants, and corticosteroids, perhaps including bronchodilators and atropine, and these animals are not considered surgical candidates. Patients that fail to respond to conservative therapy should be evaluated thoroughly.

Collapsed tracheas can often be palpated readily in the dog with a long, thin neck, but palpation is difficult in the obese dog with a short, stocky neck. Lateral radiographs, although helpful, may yield false-negative results from ballooning of the trachea or false-positive results because of the esophagus and other tissues overlying the trachea. In the awake patient, fluoroscopic examination of the trachea provides the best evaluation of the airway, including the mainstem bronchi. However, I have seen a false-negative result. Patients in respiratory distress must be handled with care, with oxygen administered as needed. Diagnostic procedures can be life-threatening to the respiratory compromised patient.

Undoubtedly, the best evaluation of the trachea is accomplished by direct visualization, tracheoscopically. This evaluation requires general anesthesia and should be performed on those patients whose owners have agreed to allow surgical treatment if recommended or whose owners are available for consultation while the patients are still under anesthesia. Recovery of patients with severe collapse from anesthesia may be difficult, if surgical treatment is not performed.

Preoperative Considerations

The client should be well informed of the prognosis and possible complications at the outset. Dogs with less than a 50% collapse of the trachea are not considered surgical candidates. The clinical signs are not usually a result of inadequate airway diameter and are better managed medically. Early surgical intervention undoubtedly has advantages, but the degree of collapse may remain static in many patients over a prolonged period.

Periodic reevaluation is considered the best approach for these patients. Patients with a 50% or greater collapse of the trachea are likely to experience respiratory distress, especially during times of excitement, when oxygen demands are high or when respiratory infections are present. These patients are considered far less likely to respond to, or already have not responded to, conservative therapy, and thus surgery should be considered.

Postoperative infection with swelling of the mucosal lining, dorsal membrane, and surrounding tissue is always of concern, because the sutures used in prosthetic implant placement are likely to penetrate the unsterile lumen of the trachea. If infections are to occur, they are most likely during the first 2 weeks after the operation. Abscessation around a prosthetic ring when antibiotics are administered is rare. The mortality rate associated with surgery is in the range of 3% to 5% and is likely to be associated with impairment of air movement during the postsurgical recovery period.

The greatest concern during the surgery is injury to the recurrent laryngeal nerves with resulting laryngeal paralysis. The nerves lie in close approximation to the dorsal lateral aspect of the trachea just caudal to the larynx, to a more ventral medial position at the thoracic inlet. The nerves are 1 mm or less in diameter in the toy breeds of dogs and are subject to injury during dissection of the trachea, tissue handling, prosthetic ring placement, or possibly even from the prosthetic ring itself if not placed properly.

Owners should be alerted to the potential need to perform a tracheostomy or laryngoplasty should laryngeal paralysis result. The patient’s laryngeal function should be checked before leaving the operating room, and a tracheostomy should be performed if needed. A permanent tracheostomy is considered preferable by the author to laryngeal tie-backs or arytenoid cartilage resection in toy breeds of dogs with laryngeal paralysis.

Laryngeal function should be evaluated while the patient is under a light plane of anesthesia as part of the preoperative examination. Drugs with analgesic properties administered as preanesthetic agents make evaluation of laryngeal function on stimulation of the larynx more difficult and should be avoided when possible. Respiratory stimulants such as doxapram (0.5 to 1.0 mg/kg IV) may be of value in assessing the larynx for normal function. Aerobic cultures should be taken directly from the trachea, avoiding the pharyngeal area. Tracheoscopy should follow, with the patient under a surgical plane of anesthesia. Oxygen can be administered directly through the bronchoscope. Brush biopsies for cytologic evaluation should be taken of the caudal trachea at the completion of the visual examination. With proper preparation, the examination, culture, and biopsy can be completed expeditiously, thus keeping the use of intravenous anesthetic induction agents to a minimum.

Radiographs of the lungs should follow, with the intubated patient under general gaseous anesthesia. Compression of the rebreathing bag provides for deep inspiratory radiographs to be made and thus for optimal evaluation of the lungs by the radiologist. Most concurrent lung disease can be ruled in or out by these techniques. The final decision whether or not to proceed with surgery is made at this time.

When surgical treatment is to follow, antibiotics should be administered parenterally A broad-spectrum bactericidal antibiotic such as enrofloxacin that is effective against gram-negative organisms, should be used until the results of tracheal culture and sensitivity testing are available. The appropriate antibiotic should be continued for 2 weeks postoperatively.

Surgical Management

Various, surgical techniques have been proposed to treat tracheal collapse. Everting plication of the dorsal tracheal membrane has been effective in moderately affected animals with rigid cartilage rings. Chondrotomy of the ventral aspect of every other tracheal ring has also been effective in some moderately affected patients with rigid cartilage rings. Resection and anastomosis are effective when few rings are collapsed, usually by trauma. Intraluminal prosthetic dilators have been useful for the short term, but they can erode the tracheal wall, stimulate granuloma formation, or interfere with mucus clearance over the longer term. Intraluminal stents have been used and may prove very effective in the future, especially when tracheal collapse is primarily within the thorax and for collapsing principal bronchi. Problems experienced with intraluminal stents include collapse when subjected to too much flexion, failure to anchor well resulting in expulsion when coughing occurs, pulmonary edema, availability of inappropriate sizes, and uneven contact between the stent and the airway wall. Granulation tissue proliferation caused by stents may result in intraluminal obstruction.

Currently, the surgical techniques most universally accepted are those that support the trachea, including the dorsal tracheal membrane, with extraluminal prosthetic devices to which the trachea is sutured. Earlier use of long sections of extraluminal prosthetic devices restricted needed flexion of the trachea, and shorter sections applied only to the ventral aspect of the trachea failed to support the sagging dorsal membrane. Current prosthetic devices provide that support. Support is reinforced by connective tissue proliferation around the prosthesis and through the holes in the prosthesis when individual ring prostheses are used. The individual ring technique consists of the placement of four to seven individual prosthetic rings around the trachea with spacing between the rings, whereas the spiral technique is essentially a continuous spiral prosthesis.

Total Ring Prosthesis

Prosthetic rings are made from 3-mL polypropylene syringe cases by cutting the syringe case into 7-to 10-mm sections with a pipe cutter over a wood dowel rod or by sawing the syringe case into sections and drilling approximately 3-mm diameter holes with either a hand drill or with a No. 11 Bard-Parker scalpel blade, or a leather punch can be used. Five holes are usually drilled, with the syringe case ring cut at the location of the sixth equally spaced hole. Angled serrated wire-cutting scissors work well for cutting the ring to decrease its size if necessary and facilitate placement of the ring around the trachea. The ends of the ring are rounded and smoothed, as are the edges of the ring and the edges of the holes, to minimize irritation after placement. The polypropylene rings can be autoclaved or sterilized by other methods. The rings can be made larger if necessary by simply spreading the ends of the rings before suturing them to the trachea. Conversely, they can be made smaller by trimming the ends of the rings, squeezing the rings, and placing a figure-of-eight suture across the cut ends of the rings through the adjacent holes after placement, but before suturing to the trachea. Polypropylene rings may break if too much pressure is applied in either expansion or compression during alteration for size and contour at the time of surgery.

The patient is positioned in dorsal recumbency with the forelegs secured caudally. A towel roll is positioned under the neck near the shoulders. A ventral midline incision is made from the larynx to just caudal to the manubrium (Figure 26-2). The sternohyoideus and sternocephalicus muscles are separated to expose the trachea; the surgeon should avoid the thyroid vein as much as possible. The thyroid vein lies between the sternocephalicus muscles in fascia on the ventral surface of the trachea. The trachea is surrounded by loose areolar tissue and receives its primary blood supply segmentally from the thyroid arteries and its nerve supply segmentally from the recurrent laryngeal nerves. Preservation of as much of the blood supply and innervation to the trachea as possible is desirable. The recurrent laryngeal nerves lie in close approximation to the dorsal lateral aspect of the trachea near the larynx coursing more ventral medially as the thoracic inlet is approached. These nerves must be handled carefully during dissection and ring placement. No tissue should be cut without knowing that the nerves are protected. The nerves should be retracted gently by grasping adjacent tissue, not the nerve itself, during dissection.
 

Curved hemostats are used to bluntly dissect a tunnel dorsally around the trachea (Figure 26-3). Care is taken to dissect between the recurrent laryngeal nerves and the trachea and to gently support the nerves as one end of the ring is grasped with the tip of the curved hemostat and gently delivered through the tunnel around the trachea. The cut end of the ring is positioned ventrally. The prosthetic ring is sutured in place with 3-0 or 4-0 polydioxanone sutures passed around a tracheal ring, up through a hole in the prosthesis, and tied. The prosthesis is grasped with forceps, and the trachea is rotated in either direction to facilitate placement of the more dorsal sutures, including at least one in the dorsal tracheal membrane.

In the occasional severe case, multiple small chondrotomies must be made through the rigid cartilage to facilitate recontouring the tracheal rings to the prostheses. These tracheal cartilages may be in the shape of an opened W. Care should be exercised to cut only the cartilage and not the tracheal mucosa.

Placement of the rings is begun just caudal to the larynx and is continued caudally with approximately the width of the prosthetic ring left between each ring placed. The neurovascular supply to the trachea is carefully left intact between the rings. Movement of the endotracheal tube during surgery is essential to prevent suture from passing through the cuff of the endotracheal tube. In addition, movement of the endotracheal tube is performed after each prosthetic ring is sutured into place to prevent inadvertent suturing of the endotracheal tube to the trachea.

Rings can be placed around the trachea deep within the thoracic inlet by gentle but strong rostral traction on the trachea. This is facilitated by grasping a distal prosthetic ring that has been sutured to the trachea (See Figure 26-3). Lateral ventra retraction of the tissue from the trachea at the thoracic inlet, including the recurrent laryngeal nerves, vagosympathetic trunk, and carotid arteries, aids in placement of these rings. With some effort, these rings can be placed far enough into the thoracic inlet that, when the patient is standing in a normal upright position after surgery, the caudal prosthetic ring will be located at the second intercostal space.
 

Severe tracheal collapse within the thoracic cavity can be approached, preferably through a right third intercostal space, for further ring placement. This is rarely done, however, because only about one additional ring can be applied rostral to the carina. No external support can be applied to a collapsed principal bronchus. When the rings can be placed as far caudally as the second intercostal space, even in patients with severe intrathoracic tracheal collapse, inspiratory efforts should result in adequate air movement to maintain normal oxygenation as the thoracic airways balloon on inspiration. The patient, however, may still cough, even to the point of exhibiting the honking cough, and is predisposed to infections and secondary changes because of the narrow airway.

Postoperative Considerations

Laryngeal function is of prime concern. It is usually evaluated before removal of the patient from the operating room. A tracheostomy is performed if deemed necessary.

Most patients do not require further surgery, nor do they require postoperative oxygen. Most are recovered in the postoperative recovery room. Analgesics are administered as indicated. Prednisolone is often given at the end of the operation to minimize effects of irritation to the airway and the recurrent laryngeal nerves. Appropriate antibiotics are continued for 2 weeks postoperatively. Antitussives and bronchial dilators are given rarely, but they are administered if deemed necessary. Any concurrent medical problems are treated as indicated because many of these patients are older dogs with other maladies.

Editor’s Note: Dr. Hobson has likely performed more tracheal ring prosthetic placements than any surgeon in the world. The surgery described here continues to be regarded as extremely valuable in the management of tracheal collapse. Some surgeons elect to place extraluminal prosthetic rings on the cervical trachea and place intraluminal stents within the thoracic trachea when indicated.

When laryngeal paralysis occurs following surgery, arytenoid tie-backs are preferred by most surgeons as the treatment of choice for the condition.

Prosthetic rings manufactured by New Generation Devices, Glen Rock, NJ, www.newgenerationdevices.com are thinner and more easily placed around the trachea than those made from syringe cases however they are more costly. The rings are currently available in 4 different diameters.

Suggested Readings

Anderson GR. Surgical correction of tracheal collapse using Teflon rings. Okia Vet 1971; 23:6.

Buback JL, Boothe HW, Hobson HP. Surgical treatment of tracheal collapse in dogs: 90 cases (1983-1993). J Am Vet Med Assoc 1996; 208:308.

Dallman MJ, Brown EM. Structural considerations in tracheal disease. Am J Vet Res 1979; 40:555.

Dallman MJ, McClure RC, Brown EM. Histochemical study of normal and collapsed trachea in dogs. Am J Vet Res 1988; 49:2l17.

Delehanty DD, Georgi JR. A tracheal deformity in a pony. J Am Vet Med Assoc 1954;125:42.

Fingland RB , Dehoff WD, Birchard SJ. Surgical management of cervical and thoracic tracheal collapse in dogs using extraluminal spiral prosthesis: results in seven cases. J Am Anim Hosp Assoc 1987;23:163.

Hobson HP. Total ring prosthesis for the surgical correction of collapsed trachea. J Am Anim Hosp Assoc 1976; 12:822

Knowles RP, Snyder CC. Chondrotomy for congenital tracheal stenosis. In: Proceedings of the American Animal Hospital Association. 1967:246.

Leonard HC. Surgical correction of collapsed trachea in dogs. J Am Vet Med Assoc 1971; 158:598.

Leonard HC, Wright JJ. An intraluminal prosthetic dilator for tracheal collapse in the dog. J Am Anim Hosp Assoc 1978;14:464.

Radlinsky MG, Fossum TW Walken MA. Evaluation of Palmaz stents in the trachea and bronchi of normal dogs. In: Proceedings of the American College of Veterinary Surgery. Chicago, IL 1995:19.

Rubin GJ, Neal TM, Bojrab MJ. Surgical reconstruction for collapsed tracheal rings. J Sm Anim Pract 1973; 14:607.

Schiller AG, Helper LC, Small E. Treatment of tracheal collapse in the dog. J Am Vet Med Assoc 1964; 145:669.

Slatter DH. A surgical method for correction of collapsed trachea in the dog. Aust Vet 1974; 50:41.

Tangner CH, Hobson HP. A retrospective study of 20 surgically managed cases of collapsed trachea. Vet Surg 1992-11-146.

Reference

1. Fingland RB, DeHoff WD, Birchard SJ. Surgical management of cervical and thoracic tracheal collapse in dogs using extraluminal spiral prostheses. J Am Anim Hosp Assoc 1987;23:163
    

Introduction

Tracheal collapse is a progressive, degenerative disease of the cartilage rings of predominantly older small and toy-breed dogs in which hypocellularity and decreased glycosaminoglycan and calcium contents lead to dynamic airway collapse during respiration. Affected animals present with signs ranging from a mild, intermittent “honking” cough to severe respiratory distress from dynamic upper-airway obstruction. Various combinations of anti-inflammatories, anti-tussives, sedatives/tranquilizers, and/or bronchodilators 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 or interventional treatment.

The most commonly performed surgery for animals with extra-thoracic tracheal collapse is the placement of extra-luminal ring prostheses. Using a ventral midline cervical approach, extra-luminal support rings are carefully placed around the trachea. This technique has a reported 75% to 85% overall success rate in one report of 90 dogs for reducing clinical signs, however there is significant associated morbidity.¹ In the same study, 5% of animals died peri-operatively, 11% developed laryngeal paralysis from the surgery, 19% required permanent tracheostomies (half within 24 hours), and ~23% died of respiratory problems with a median survival of 25 months. In addition, only 11% of the dogs in this study had intra-thoracic tracheal collapse (all dogs had extra-thoracic tracheal collapse) and the authors advised against this technique in patients with intra-thoracic tracheal collapse as the resulting morbidity was unacceptably high.

The combination of surgical risk and the inability to adequately treat intra-thoracic tracheal collapse led to the evaluation of minimally-invasive surgical techniques used in humans for potential treatment options. Interventional radiology involves the use of contemporary imaging modalities such as fluoroscopy to gain access to different structures in order to deliver materials for therapeutic purposes. Specially designed intra-luminal metallic stents have been placed within the human tracheobronchial system using these techniques to treat chondromalacia, malignant obstruction, or strictures and stenoses. A number of stents have been previously evaluated in the canine trachea, including both balloon-expandable stents (Palmaz) and self-expanding (Stainless steel, Laser-cut nitinol, Knitted nitinol) stents.^2-4 The vastly superior flexibility makes the use of self-expanding metallic stents (SEMS) particularly appealing for tracheal use. Clinical improvement rates in 75% to 90% of animals treated with intra-luminal SEMS have been reported.^3,4 Immediate complications were typically minor although there was a reported peri-operative mortality rate of approximately 10%, a rather high figure compared to the author’s experience. Late complications included stent shortening, excessive granulation tissue forming within the trachea, progressive tracheal collapse, and stent fracture.

Neither surgery nor stenting are cures for tracheal collapse, and to the author’s knowledge, neither has been shown to slow the progression of the disease. When used appropriately in the proper patients, both can significantly improve the patients’ quality of life when medications alone are no longer adequate. Below are this author’s criteria for patient selection, method of stent selection, and technique for placing intra-luminal tracheal stents. It should be noted that the majority of the following information is based solely on experience as veterinary research on this subject is currently in its infancy.

Patient Selection

The diagnosis of tracheal collapse and other forms of respiratory dysfunction have been described elsewhere. The readers are referred to other materials for a complete discussion of respiratory system evaluation and related diagnostic procedures. Due to the relatively high morbidity and mortality rates associated with surgery or stenting of the trachea, these procedures are avoided when possible. Other primary or secondary respiratory disorders must be evaluated concurrently or addressed prior to more invasive therapies for tracheal collapse. Animals with concurrent cardiac and/or pulmonary disease can often benefit substantially from medical treatment such that more invasive tracheal collapse treatments can be avoided or postponed.

Whether considering surgical rings or intra-luminal stenting it is imperative that aggressive medical management has been attempted and has failed to provide a “reasonable quality of life” for the patient. In the author’s opinion, this includes anti-inflammatory doses of corticosteroids, anti-tussives, and the general management considerations described above. An exception to this rule is the emergent, intubated patient which has failed attempts at extubation. An owner’s inability to administer medication is not a valid reason to perform one of these invasive procedures as the majority of patients will still require medication following treatment. In addition, while the “grade” of tracheal collapse (Grades I, II, III, or IV) has been described in the literature, the author will not treat based upon the grade of collapse alone. The success of either of these procedures must be evaluated in light of the owners’ expectations. It is the veterinarian’s responsibility to properly inform the owner that these are largely palliative procedures and the disease is likely to progress.

Rings or Stent?

Whether to perform surgery versus stenting is a complex, controversial and unresolved question. Decisions must be made on an individual case basis, however some basic guidelines can be used. In my opinion, if significant intra-thoracic tracheal collapse is present then surgery is either unlikely to resolve the problem or be associated with excessive morbidity and therefore an intra-luminal stent should be considered. If only cervical tracheal collapse is present, then extra-luminal surgical rings may be considered. An exception may be in a geriatric patient or one with excessive co-morbidities (extensive cardiac or pulmonary disease, endocrinopathies, etc.) in which prolonged anesthesia or healing associated with surgery may present more of a concern. In addition, the author would prefer to avoid intra-luminal stent placement in younger animals as long-term follow-up (> 5 years) in tracheal stented animals has not yet been performed.

The patient with diffuse cervical and intra-thoracic tracheal collapse is an even greater dilemma. One can argue that an intra-luminal stent for the intra-thoracic collapse and surgical rings for cervical collapse might avoid some of the potential complications associated with very long tracheal stents spanning the thoracic inlet, however the alternative view would be that this approach would combine the potential complications associated with both procedures. In these cases, the author is currently placing a single, long stent to span both the intra- and extra-thoracic trachea. Others are placing stents intra-thoracically and surgical rings on the cervical trachea.⁵

^{Bronchial Collapse}

There remains much debate concerning the use of intra-luminal stents in patients with mainstem bronchial collapse. Unfortunately, there is currently no data available to recommend or oppose the routine use of intra-luminal stents in these patients, and therefore, regrettably, the author can only offer an opinion. The questions raised are two-fold:

(1) Should stents be placed within collapsing mainstem bronchi? I do not recommend stenting of collapsing mainstem bronchi. Not only will bronchial stents “cage-off” other bronchi and consequently prevent drainage from affected lung lobes, but secondary and tertiary bronchi will continue to collapse and therefore the benefit achieved will likely be minimal, and temporary, when compared to the risks. Theoretically, there may be animals in which focal mainstem bronchial collapse has been diagnosed in which placement of short bronchial stents could provide some benefit.

(2) Should tracheal stents be placed in patients with concurrent tracheal and mainstem bronchial collapse? Certain patients will benefit from tracheal stenting, even when concurrent mainstem bronchial collapse is present. The patient should be carefully evaluated to determine the animal’s primary clinical signs. Tracheal collapse can lead to dyspnea, coughing/honking, or both. Bronchial collapse will usually manifest as a cough, expiratory dyspnea, or both. When both tracheal and bronchial collapse are present, the results following tracheal stent placement become less predictable. If dyspnea is the major clinical sign and intra-thoracic tracheal collapse is present, a tracheal stent can help relieve the dynamic obstruction. If the patient’s primary problem is coughing, then it becomes difficult to determine if the coughing is secondary to the tracheal collapse or bronchial collapse. In these patients, the author always warns the owner that continued coughing will likely be present as the bronchial collapse will continue. In addition, in the author’s experience, it appears that continued, intractable coughing will cause repeated cycling of the stent and may increase the risk of subsequent fracture, or predispose to the formation of excessive granulation tissue. Persistent coughing must be treated aggressively to minimize the risk of these complications.

Expectations/Risks/Discussion with the Owner

An in-depth discussion with the owner concerning the risks and expectations should take place once the decision has been made to consider tracheal stenting. Neither surgery nor stenting has been demonstrated to slow the progression of tracheal collapse and both techniques are considered palliative. Clinical improvement rates in 75% to 90% of animals treated with intra-luminal SEMS have been reported, and immediate complications were mostly minor although there was a peri-operative mortality rate of approximately 10% in one report.^3,4 Late complications can include stent shortening, excessive granulation tissue, progressive tracheal collapse, and stent fracture. Continued coughing should be anticipated in patients with concurrent bronchial collapse and these patients may have a worse prognosis. In addition, the vast majority of patients will require continued medical therapy.

Stent Selection

A general review of stents is beyond the scope of this chapter, but a brief discussion of certain stent characteristics is necessary to understand how one selects an appropriate stent type and size. This discussion will not include balloon-expandable metallic stents (BEMS) as SEMS are exclusively being used to treat tracheal collapse in animals. In their resting state (deployed, or outside of the delivery system), SEMS are expanded to their stated, pre-determined dimensions. For example, a 10 mm diameter x 70 mm long SEMS will be 10 mm wide and 70 mm long if deployed from the delivery system. Following manufacturing, an SEMS is compressed and mounted onto a delivery system using a number of different techniques. The relatively small delivery system (compared to the expanded stent diameter) allows introduction through very small holes (vascular sheath or endotracheal tubes, for instance). During placement, as the delivery system sheath is retracted, the stent expands back to its original dimensions.

Stent Material

The majority of stents being manufactured today are made of nitinol, a nickel (“Ni”)-titanium (“Ti”) alloy developed by the Naval Ordinance Laboratory (“NOL”) which is classified as a shape-memory metal. This characteristic means that nitinol assumes a weakened, deformable state (Martensite phase) at low temperatures but it will return to, and maintain, its original shape at body temperature (Austenite phase). Laser-cut nitinol stents are cut from hollow tubes of nitinol and at cooled temperatures, the metal’s properties change allowing compression of the stent onto a delivery system. Upon returning to ambient temperature, the stent favors its original design which is achieved upon deployment from the delivery system. Laser-cut nitinol SEMS are currently not recommended by the author for the treatment of diffuse cervical and intra-thoracic tracheal collapse in veterinary patients due to an unacceptably high occurrence of stent fracture (personal experience). However, others have had success placing shorter laser-cut nitinol stents in the intra-thoracic trachea only.⁵ Woven, knitted, or mesh stents are designed to be compressed onto a delivery system at normal temperatures through specific design modifications. While the design of these stents facilitates placement onto a delivery system, there is a wide range of foreshortening that occurs from the design changes as well. Examples of more commonly used nitinol stents in veterinary patients currently include mesh stents (Vet Stent-Trachea, Infiniti Medical) or knitted stents (Ultraflex, Boston Scientific). Other commercially available stents used for tracheal collapse are made of stainless steel or similar alloys (Wallstent, Boston Scientific) (Figure 26-4).
 

Foreshortening

The vast majority of tracheal stents currently placed in veterinary patients are mesh or knitted SEMS. One important characteristic of these stents which must be anticipated is the subsequent “foreshortening” that will occur during deployment. “Foreshortening” refers to the shortening of the stent that is encountered as it is released from the delivery system. The stent size, as indicated on the packaging, refers to the diameter and length at complete expansion. If the stent does not achieve complete expansion (i.e. the lumen in which it is placed prevents complete radial expansion to its original diameter), the stent will be longer than expected. In other words, the stents are significantly longer when viewed in the compressed state on the delivery system. As the stent expands radially it shortens, and as such, the ultimate length of the stent is inversely proportional to the degree of expansion (The less the stent expands, the longer it will be). This is an extremely important property of knitted and mesh stents which must be recognized and accounted for during the stent selection process. For example, the more over-sized the stent chosen (diameters over 10% to 15% greater than the diameter of the trachea), the longer the stent will be when initially deployed, and the greater the tendency for the stent to shorten over time as it gradually expands to its original, predetermined diameter. This gradual shortening must be accounted for when choosing the appropriate stent length; Over-sized stents should span additional length of normal trachea beyond the area of collapse as future shortening is anticipated. In the author’s experience, stent shortening typically occurs at the cranial end of the stent in a caudal direction over time, most likely due to the fact that the cervical trachea is usually larger in diameter than the intra-thoracic trachea. This difference in diameter seems to facilitate greater radial expansion of the stent in the cervical trachea. As a result, the cranial aspect of the stent slowly migrates in a caudal direction. When collapse extends to the larynx, the stent is placed to extend as far cranially as possible without contacting the cricoid cartilage. If the over-sized stent gradually shortens over time, a single extra-luminal ring can be placed surgically if tracheal collapse rostral to the stent recurs and clinical signs redevelop.

Reconstrainability

While foreshortening can complicate the process of choosing the appropriate SEMS for tracheal collapse, another characteristic of some of these stents is “reconstrainability”. This feature allows the operator to re-sheath a partially deployed stent in order to reposition the stent and deploy it elsewhere or remove it completely if necessary. Generally, the mesh stents (Vet Stents-Trachea^TM [nitinol], Wallstents^TM [Stainless steel]) are reconstrainable to varying degrees, while the knitted stents (Ultraflex^TM [nitinol]) are not reconstrainable. Obviously, it is important to know beforehand whether the stent is reconstrainable. In addition, although a stent may be considered “reconstrainable”, that does not mean that the stent can be removed once fully deployed. While some stents can be removed following placement, most stents currently used for tracheal collapse in veterinary patients are designed to remain in place, and as such removal would be very difficult.

Stent Sizing

In order to choose an appropriately sized stent, it is important to determine (1) the length of the collapse, and (2) the diameter of the trachea. The single most effective way to minimize peri-operative stent placement complications when learning this procedure is to appropriately determine these tracheal dimensions.

Stent Length: Simple radiography is not adequate in identifying the length of collapse as different areas of collapse will be apparent during different phases of respiration (Figure 26-5). While tracheoscopy has been historically regarded as the “gold standard” for identifying tracheal collapse, this procedure requires general anesthesia which can add significant risk in these often debilitated patients. The author prefers to identify the length of collapse in a fully awake animal using real-time fluoroscopy. In addition, it is important to induce coughing when possible as the extreme airway pressures subsequently generated will often reveal more extensive collapse than identified during more relaxed breathing (Figure 26-6). Anatomical landmarks are then identified to record the cranial-most and caudal-most extent of the collapse. In addition, mainstem bronchial collapse can often be identified during fluoroscopy and should be noted when present.
 

On occasion, a previously well-managed patient will present that is unable to be extubated following general anesthesia for an unrelated procedure. Under these circumstances, the awake fluoroscopy technique described above will not be possible. For these rare cases, the author uses a home-made “negative-pressure ventilation device” (Figure 26-7). Following adequate pre-oxygenation with manual positive pressure ventilations, this apparatus is connected to the endotracheal tube and the dosing syringe plunger is withdrawn to 10 to 15 cm H₂O on the sphygmomanometer as a radiograph is taken to document the location of collapse (Figure 26-8).

Once the length of the collapse has been determined, the stent length is chosen to extend approximately 1 cm beyond the cranial and caudal extents of collapse. If the entire length of the trachea is affected, the stent length is usually chosen to extend from approximately 1 cm cranial to the carina to 1 cm caudal to the cricoid cartilage of the larynx. Alternatively, one could choose to place an intra-thoracic tracheal stent alone and place surgical rings on the cervical trachea.
 

For shorter lengths of collapse, one must decide whether the animal will benefit from complete tracheal stenting versus covering just the shorter affected segment. One study identified a potential increased risk of complications in animals receiving longer Wallstents, however this finding was not corroborated in another study.^3,4 A correlation between stent length and complication rate has not yet been apparent in this author’s experience and, as such, if progression of the disease is expected, the patient will generally receive stenting of the majority of the trachea. In general, the author avoids complete tracheal stenting in younger patients when possible. In older patients, or those cases in which the client can only afford a single procedure, a discussion concerning the risks and benefits of complete tracheal stenting is necessary. In general, the price of a stent is not determined by its dimensions (a 40 mm long stent is usually the same price as a 90 mm stent). Therefore, there is no financial benefit to placing a shorter stent.

Stent Diameter: The maximal tracheal diameter is typically determined at the time of stent placement to avoid having to repeat general anesthesia. It is therefore necessary to have a number of different stent sizes available. Alternatively, the stent sizing process can take place during a separate general anesthetic episode and the appropriate stent size subsequently ordered. It is the veterinarian’s judgment as to whether an additional anesthetic episode places the patient at significant risk. It is imperative that the stent diameter is not chosen based upon resting survey radiographs. Otherwise, the stent diameter will typically be under-sized, resulting in subsequent stent migration. In addition, the author avoids using standard “magnification” values assigned to different radiographic units. These values tend to be “estimations” and are not sufficiently accurate for the fine measurements necessary in these cases.

The author places a measuring catheter within the esophagus in order to account for radiographic magnification. Alternatively, some other measuring device can be placed externally and included in the radiograph, although placement within the esophagus is ideally located directly beside the trachea. With the esophageal marker catheter technique, the patient is placed in lateral recumbency following intubation. A wet hydrophilic guidewire^a and flushed marker catheter^b combination are advanced into the mouth. Using fluoroscopic guidance, the guidewire is gently advanced down the esophagus and the marker catheter is advanced over-the-wire. The soft guidewire is always advanced first to avoid damage to the esophagus by the relatively stiffer marker catheter. The marker catheter is placed within the esophagus such that the radio-opaque marks extend along the location of the tracheal collapse. The guidewire can then be withdrawn. Under fluoroscopic guidance, the endotracheal (ET) tube is withdrawn until the distal-most aspect is just beyond the larynx and the cuff is gently re-inflated. Positive pressure ventilation of 20 cm H₂O is temporarily performed to achieve maximal tracheal expansion as a radiograph is taken. The radio-opaque marks on the marker catheter are 10 mm apart; this distance is measured on the radiograph and used to determine the radiographic magnification that is then used to extrapolate the actual maximal diameters of both the intra-thoracic and cervical trachea (Figure 26-9A). It is important to take maximal measurements of BOTH the cervical and intra-thoracic trachea as these measurements can vary dramatically.
 

The stent diameter is usually chosen to be 10% to 20% greater than the maximal tracheal diameter to minimize chances of subsequent stent migration. The author generally inventories stents in 2 mm diameter increments (i.e., 8 mm, 10 mm, 12 mm, and 14 mm diameter) and in the most commonly used lengths. The cervical trachea is routinely larger in diameter than the intra-thoracic trachea. Stent sizing can be complicated when the difference in these two measurements varies dramatically. When the two diameters are similar (within 2 mm), the stent diameter chosen is at a minimum equal to the maximal tracheal diameter and typically no more than 10% to 20% larger than the maximal diameter.

Example 1: A dog with maximal intra-thoracic tracheal diameter of 8mm and maximal cervical tracheal diameter of 10mm would likely receive a 12 mm diameter stent. When the discrepancy between the cervical and intra-thoracic trachea is 3 mm or greater, a stent diameter that is at least 10% to 20% larger than the intra-thoracic tracheal diameter or the average of the two measurements is chosen as long as the stent will be well seated within the intra-thoracic trachea to prevent cranial migration.

Example 2: A dog with a maximal intra-thoracic tracheal diameter of 8 mm and maximal cervical tracheal diameter of 12 mm would likely receive a 12 mm (or 10 mm) diameter stent. However, one must also consider the relative length of the stent that will be located in the smaller diameter trachea. If only about 20% of the stent will be located in the 8 mm diameter portion of the trachea, adequate tracheal wall contact may not be achieved with the 10 mm stent. Alternatively, if 80% of the stent will be within the 8 mm diameter portion of the trachea, a 10 mm diameter stent may be sufficiently seated within this location to prevent migration. The advantage of the 10 mm diameter stent is that the length will be easier to determine as it will more closely achieve full expansion and therefore the length will be closer to its predetermined length.

In both examples above, if a 12 mm diameter stent was chosen, a shorter length stent would be required as the stent would not reach its full diameter and therefore the stent length would be longer than anticipated had full expansion been achieved. These calculations are intended as guidelines and cannot be used for every case.

^a Weasel Wire, Infiniti Medical, Haverford, PA. 
^b Marker Catheter, Infiniti Medical, Haverford, PA.

Stent Placement Technique

The following description applies to placement of mesh SEMS (Vet Stents-Trachea^TM, Wallstents^TM). For information regarding placement of knitted SEMS, the readers are referred to alternate resources.

General Anesthesia and Preparation

Anesthesia protocols differ among institutions, however the author prefers a rapid induction and recovery. An anti-tussive/ tranquilization combination such as butorphanol (0.2 to 0.3 mg/ kg) and acepromazine (0.01 mg/kg) can be an effective premedication when necessary, however premedications are routinely avoided unless intravenous catheterization creates excessive anxiety and respiratory distress. Pre-oxygenation of the patient before handling is routinely performed. Unless contraindicated, a combination of intravenous propofol and diazepam are used with minimal inhalant anesthesia concentrations. Propofol CRIs are occasionally used. The use of peri-operative antibiotics is debatable and chosen on an individual case basis. Unless contraindicated, these patients typically receive one perioperative dose of dexamethasone SP (0.1 to 0.25 mg/kg IV).

The largest diameter ET tube possible should be selected (at least 4 mm inner diameter) to facilitate unrestricted passage of the stent delivery system through the tube while permitting simultaneous oxygen delivery and ventilation during the procedure. An ET tube with a radio-opaque line or markers should always be used when possible to help avoid inadvertent deployment of the stent within the tube. The use of sterile ET tubes is debatable and not routinely required by the author. Following intubation, the patient is placed in lateral recumbency. Subsequent measurements are used to determine the tracheal stent diameter as described above. The radiographic landmarks previously obtained during awake fluoroscopy identifying the length of the collapse are compared with those of the esophageal marker catheter to determine the length of stent necessary.

Stent Placement

Once the appropriately sized stent is chosen, it is removed from its packaging using sterile technique. The stent is prepared and saline flushed according to manufacturer recommendations. The operator is encouraged to practice these techniques outside of the patient before introducing the delivery system into the ET tube. ALL MANIPULATIONS SHOULD BE PERFORMED UNDER DIRECT FLUORSCOPIC GUIDANCE. A right-angle bronchoscope adapter (Figure 26-10) is attached to the ET tube to facilitate passage of the stent delivery system through the tube while maintaining the anesthesia circuit system. The delivery system must pass easily and without friction. Occasionally it is necessary to remove the diaphragm on the bronchoscope adapter to permit unrestricted passage of the delivery system. Before passing the stent, the patient should be positioned such that the cervical and intra-thoracic trachea lie in a straight line to facilitate unrestricted passage of the relatively inflexible delivery system (Figure 26-9B). This position will minimize trauma to the tracheal wall during advancement of the delivery system. The author always places tracheal stents under fluoroscopic guidance although some have performed these techniques using endoscopic assistance alone. In addition, passage of the delivery system and stent placement can induce a coughing reflex. The animal should be sufficiently anesthetized to avoid a coughing episode during stent deployment.
 

The radio-opaque stent is easily visualized under fluoroscopy, even when constrained within the delivery system. Once the distal end of the stent has been positioned appropriately, stent deployment can proceed. During deployment, the entire stent and delivery system combination can be gently pulled craniad if the stent is initially placed too caudally, however the entire system cannot be advanced caudally if placement is inappropriately cranial. For this reason, some prefer initially to place the distal aspect of the stent slightly (~0.5 to 1cm) caudal to the desired final location. To initiate stent deployment, with one hand on the hub (or the cannula), and the other hand on the Y-piece (sheath), gently withdraw the Y-piece (sheath) while simultaneously advancing the hub (cannula) in equal proportions (Figure 26-11). If done appropriately, as stent deployment proceeds, the distal end of the stent will remain in the same location throughout deployment. Under no circumstances should the cannula (hub) be advanced while the sheath remains stationary. This will force the stent caudally and traumatize the tracheal mucosa. These same circumstances apply to the process of stent reconstrainment. If the operator is unhappy with the location of the partially deployed stent, reconstrainment should be performed via simultaneous withdrawal of the cannula and advancement of the sheath in order to avoid dragging the stent across the tracheal mucosa. The operator should read the manufacturer’s instructions to determine the degree to which stent deployment can occur before stent reconstrainment is no longer possible.
 

Following complete stent deployment, carefully remove the delivery system. This should be performed under fluoroscopic guidance to ensure the delivery system nose-cone does not engage the distal end of the stent upon removal. Radiographs are taken to document the final position of the stent within the trachea (Figure 26-9C). The patient is recovered immediately, typically in an intensive care unit setting, and often within an oxygen cage. The use of butorphanol (0.1 to 0.2 mg/kg IV) and/or acepromazine (0.005 to 0.01 mg/kg IV) can be useful to facilitate smooth recovery from general anesthesia.

Post-Operative Care and Follow-Up

Patients are routinely discharged one or two days post-stenting with a 3 to 6 week tapering dose of prednisone (initial dose of 1 to 2 mg/kg/day PO), continued anti-tussive therapy (Hydrocodone 0.25 mg/kg PO q6 to 12 hours or higher doses if tolerated), and 10 to 14 days of broad-spectrum oral antibiotics. Patients with bronchial collapse and/or an observed “expiratory push” during exhalation may benefit from bronchodilator therapy as well.

Owners should be warned to anticipate an initial dry cough that should improve over the following 3 to 4 weeks. If the patient has documented bronchial collapse, the owners should expect continued coughing in the future. Aggressive medical management of coughing is imperative for a good long-term outcome. It is the author’s anecdotal experience that continued coughing increases the risk of both granulation tissue formation and stent fatigue/fracture. High doses of anti-tussive medications and inhalation steroids have been useful when routine therapy is inadequate. The majority of patients will require life-long medication following tracheal stenting. The initial recheck examination is approximately two weeks post-stenting or sooner if problems arise. Repeat examinations are performed regularly (every 3 to 6 months if possible) or sooner if the patient’s clinical signs worsen.

Disclosure: The author is a consultant for Infiniti Medical, LLC and has been involved in the specifications chosen for the Vet Stent-TracheaTM and Delivery System.

References

1. Buback JL, Boothe HW, and Hobson HP. Surgical treatment of tracheal collapse in dogs: 90 cases (1983-1993) Journal of the American Veterinary Medical Association 1996; 208(3):380-384.
2. Radlinsky MG, Fossum TW, Waler MA, et al. Evaluation of the palmaz stent in the trachea and mainstem bronchi of normal dogs. Veterinary Surgery 1997; 26(2):99-107.
3. Norris JL, Boulay JP, Beck KA, et al. Intraluminal self-expanding stent placement for the treatment of tracheal collapse in dogs (abstr), in Proceedings, 10th Annual Meeting of the American College of Veterinary Surgeons 2000.
4. Moritz A, Schneider M, and Bauer N. Management of advanced tracheal collapse in dogs using intraluminal self-expanding biliary wallstents. Journal of Veterinary Internal Medicine 2004; 18:31-42.
5. Krahwinkel DJ. Tracheal collapse: Is surgery an option?, in Proceedings, 15th Annual Meeting of the American College of Veterinary Surgeons, San Diego, CA, 2005.
    

Tracheal anastomosis is indicated for management of benign and malignant tracheal stenoses, traumatic tracheal disruption, and segmental tracheomalacia. Important preoperative considerations include localization of the lesion, determination of the proximal and distal margins of the lesion, and, in the case of malignant lesions, evaluation of the animal for distant metastases. Plain film radiography, tracheoscopy, and computed tomography are helpful in localization of tracheal lesions.

Tracheal anastomosis in veterinary patients typically is accomplished by apposition of circumferentially divided tracheal cartilages with sutures placed in simple interrupted fashion (split-ring technique).¹ Alternative techniques such as overriding segments, creation of mucosal flaps, and apposition of annular ligaments are less desirable because these techniques are technically more difficult or result in critical anastomotic stenosis.^1,2 In one study, simple continuous and simple interrupted suture techniques for tracheal anastomosis after large-segment tracheal resection were compared in dogs. Differences in surgical time and anastomotic stenosis were not clinically significant.³

Tension has a profound effect on anastomotic healing and is the major factor limiting the extent of tracheal resection. Tracheal anastomoses consistently are successful in mature dogs when tension on the anastomosis is less than 1750 g.⁴ Unfortunately, attempts to correlate grams of tension with number of tracheal cartilages have produced widely disparate results.⁵ In general, 25% of the trachea (8 to 10 tracheal cartilages) can be resected in a mature dog with consistently satisfactory results. In young animals and in animals with primary tracheal disease, this number may be significantly lower.⁶

Surgical Techniques

Cervical Trachea

Preoperative planning is imperative. An endotracheal tube with a high-volume, low-pressure cuff should be used. Ideally, the endotracheal tube should be positioned proximal to the affected tracheal segment, and the entire procedure should be performed “over” the endotracheal tube. In patients with significant luminal compromise, the endotracheal tube should be positioned distal (orad) to the lesion for the surgical approach and the initial tracheal dissection. Tracheal anastomosis necessitates intraoperative manipulation of the endotracheal tube and, on occasion, direct intubation of the distal segment of the trachea. A sterile endotracheal tube should be available for intraoperative intubation of the distal segment of the trachea. The endotracheal tube cuff must be deflated when the tube is repositioned within the trachea and then reinflated before the procedure continues. Prophylactic administration of a broad-spectrum antibiotic is recommended.

The patient is positioned in dorsal recumbency, and the ventral cervical region is prepared for aseptic surgery. The skin and subcutaneous tissues are incised from the larynx to the manubrium. The trachea is exposed by midline separation of the paired sternocephalicus and sternohyoideus muscles. The segment of trachea to be resected is determined based on preoperative evaluation and intraoperative inspection and palpation. The lateral pedicles are dissected from the trachea along a segment that includes two cartilage rings proximal and two cartilage rings distal to the proposed margins of the excision. Carrying the lateral pedicle dissection beyond the proposed margins of excision facilitates manipulation of the proximal and distal tracheal segments and placement of primary anastomotic and tension sutures. Traction sutures (3-0 polydioxanone, SH-1 taper needle, 70 cm) are placed around the right and left lateral aspects of the second tracheal cartilage proximal to the cartilage to be incised. The swaged-on needle is left in place, and the suture is looped but not tied. These traction sutures facilitate manipulation of the proximal tracheal segment and are used as tension sutures after the primary anastomosis is completed.

The segment of trachea is excised by circumferentially incising one tracheal cartilage at each end of the segment (Figure 26-12). Care is taken to incise the tracheal cartilages circumferentially in two equal halves. If the endotracheal tube was initially positioned distal to the lesion, the cuff is deflated, the endotracheal tube is directed into the proximal tracheal segment, and the endotracheal tube cuff is reinflated. On both sides of the trachea, the swaged-on arm of the lateral traction suture is passed around the second complete tracheal cartilage distal to the incised tracheal cartilage. These sutures are used to approximate and maintain apposition of tracheal segments and to facilitate rotation of the trachea for placement of primary anastomotic sutures (Figure 26-13).

The proximal and distal circumferentially incised tracheal cartilages are approximated using the pre-placed lateral tension sutures (Figure 26-14). Accurate alignment of the two split cartilages is important. The primary anastomosis is created using 4-0 polydioxa-none suture placed in a simple interrupted pattern approximately 3 mm apart (Figure 26-15). Each suture incorporates the split proximal and distal tracheal cartilages. All sutures enter the lumen of the trachea.
 

The dorsal tracheal membrane is exposed by rotating the trachea with the preplaced lateral tension sutures (Figure 26-16). Anastomotic sutures are placed in the dorsal tracheal membrane in a manner that ensures accurate apposition and an airtight seal.

The lateral tension sutures are tied after the primary anastomosis is complete (Figure 26-17). A third tension suture is placed on the ventral aspect of the trachea. The tension sutures should be tight enough to relieve tension from the primary anastomotic sutures, but they should not cause deviation or overlapping of the apposed ends of the proximal and distal segments of the trachea.
 

Thoracic Trachea

The thoracic segment of the trachea is approached through a right third intercostal thoracotomy. The technique for resection and anastomosis of the thoracic segment is similar to the technique described for the cervical segment of the trachea. Direct intubation of the proximal segment of the trachea intra-operatively usually is necessary. Direct intubation of an isolated primary bronchus may be necessary to maintain ventilation. Preoperative planning and technical expertise are necessary to ensure success.

Postoperative Considerations

Brief, atraumatic tracheal suctioning after extubation is helpful to remove clotted blood from the lumen of the trachea. The patient should be observed closely for respiratory distress for 12 to 24 hours after surgery. Postoperative respiratory distress can result from laryngeal or pharyngeal edema, occlusion of the tracheal lumen at the anastomotic site, or iatrogenic laryngeal paralysis from intraoperative recurrent laryngeal nerve injury. Antitussives and glucocorticoids are administered as needed to reduce inflammation and to suppress coughing.

The nature of tracheal wound healing ensures some degree of anastomotic stenosis. Periodic endoscopic examination of the trachea after anastomosis is helpful to evaluate wound healing and anastomotic stenosis. Anastomotic stenosis usually is not clinically significant in sedentary patients until the tracheal lumen is compromised by 50 to 75%.⁷ Meticulous, atraumatic surgical technique and elimination of tension on the anastomosis usually result in a successful outcome.

References

1. Hedlund CS. Tracheal anastomosis in the dog: comparison of two end-to-end techniques. Vet Surg 1984;13:135.
2. Lau RE, Schwartz A, Buergelt CD. Tracheal resection and anastomosis in dogs. J Am Vet Med Assoc 1980; 176:134.
3. Fingland RB, Layton CE, Kennedy GA, et al. A comparison of simple continuous versus simple interrupted suture patterns for tracheal anastomosis after large-segment tracheal resection in dogs. Vet Surg 1995,24:320.
4. Cantrell JR, Folse JR. The repair of circumferential defects of the trachea by direct anastomosis: experimental evaluation. J Thorac Cardiovasc Surg 1961,42:589.
5. Vasseur PB, Morgan JP. The trachea. In: Gourley IM, Vasseur PB, eds. General small animal surgery. Philadelphia: JB Lippin-cott, 1985.
6. Maeda M, Grillo HC. Effects of tension on tracheal growth after resection and anastomosis in puppies. J Thorac Cardiovasc Surg 1973;65:658.
7. McKeown PP, Tsuboi H, Togo T, et al. Growth of tracheal anastomoses: advantages of absorbable interrupted sutures. Ann Thorac Surg 1991;51:636.
    

Introduction

A permanent tracheostomy is a stoma in the ventral tracheal wall created by suturing tracheal mucosa to skin. Tracheostomy tubes are not needed to maintain lumen patency following this procedure. Tracheostomas are maintained for life or until the stoma is surgically closed. Permanent tracheostomies are recommended for animals with upper respiratory obstructions causing moderate to severe respiratory distress that cannot be successfully managed by other methods. Dogs and cats with cyanosis or severe dyspnea at rest or with minimal exertion are candidates. Respiratory distress is commonly associated with laryngeal dysfunction secondary to laryngeal collapse or neoplasia, and sometimes nasopharyngeal or proximal tracheal obstruction. Before creating a tracheostoma, it is important to establish the clients willingness and ability to provide postoperative care. Although most patients requiring a permanent tracheostomy function much better after surgery, some clients will refuse the procedure and elect less beneficial surgical procedures or euthanasia.

Surgical Technique

A permanent tracheostomy is performed with the anesthetized patient in dorsal recumbency.^1-3 The skin of the ventral and lateral neck is clipped and aseptically prepared for surgery. On the operating table, the patient’s forelegs are positioned caudally along the chest, and then the animal’s neck is elevated and extended with a dorsal cervical pad. The proximal cervical trachea is exposed with a ventral cervical midline incision beginning at the distal larynx and extending caudally 8 to 10 cm. The paired sternohyoid muscles are separated and are retracted laterally to visualize the trachea. The endotracheal tube cuff is advanced distal to the proposed tracheostomy site. The surgeon creates a tunnel dorsal to the trachea from the third to sixth tracheal cartilages and, using this tunnel, apposes the sternohyoid muscles dorsal to the trachea with horizontal mattress sutures to create a muscle sling (Figure 26-18). The muscle sling serves to deviate the trachea ventrally reducing tension on the mucosa-to-skin sutures. Beginning with the second or third tracheal cartilages, a rectangular segment of tracheal wall three to four cartilage widths long and one-third the circumference of the trachea in width is outlined. (See Figure 26-18) Using a #11 scalpel blade, the cartilage and annular ligaments are incised to the depth of the tracheal mucosa. The surgeon elevates a cartilage edge with thumb forceps and dissects the cartilage segment from the mucosa using the blunt edge of the scalpel blade. If tracheal cartilages show any weakness or tendency to collapse, place one or two prosthetic tracheal rings cranial and caudal to the stoma. A similar segment of skin is excised adjacent to the stoma. If the patient has loose skin folds or abundant subcutaneous fat, larger segments of skin are excised to help prevent skin fold occlusion of the stoma. Excess fat is excised in obese patients to allow direct contact of the skin and peritracheal fascia. The surgeon sutures the skin directly to the peritracheal fascia laterally and the annular ligaments proximal and distal to the stoma with a series of interrupted intradermal sutures (3-0 or 4-0 polydioxanone or poliglicaprone 25) without entering the tracheal lumen. These skin-peritracheal sutures promote adhesion of the skin to the trachea and are important in reducing postoperative skin fold problems, seroma formation, and tension on the stomal sutures. An “I” or “H” shaped incision is made through through the mucosa. The mucosa is folded over the cartilage edges and sutured to the edges of the skin with approximating sutures (4-0 monofilament absorbable) (Figure 26-19). Simple interrupted sutures are placed at the corners and a simple continuous pattern is used along the sides of the stoma. Sutures are spaced approximately 2 mm apart. Precise apposition is important to minimize tracheostomal stenosis but is not always possible. Precise apposition is not possible if the tracheal mucosa is disrupted during dissection or previous tube tracheostomy, or of poor quality due to disease. If the patient does not have enough mucosa to cover the incised cartilage edges and annular ligaments, the surgeon should appose as much mucosa to the skin as possible and allow the exposed areas to heal by second intention. If necessary, sutures are passed around or through adjacent cartilages or annular ligaments. Skin edges are apposed proximal and distal to the stoma with simple interrupted or cruciate sutures. Blood and mucus are suctioned from the stoma before the animal recovers from anesthesia.
 

Permanent tracheostomy following total laryngectomy requires the creation of a tracheostoma after the transected end of the trachea is closed or deviated to the skin.^3,5 Closure of the transected trachea is accomplished by preserving a flap of dorsal tracheal membrane from the more proximal trachea that can be folded over the exposed lumen of the distal trachea and then sutured. Alternatively, the transected distal trachea is closed by placing a series of interrupted horizontal mattress sutures to appose the dorsal tracheal membrane to the cartilage. After using either of these closure techniques a permanent tracheostomy is performed as described previously.

Another option after total laryngectomy is to incorporate the distal tracheal end into the tracheostoma. This is accomplished by apposing the sternohyoid muscles dorsal to the distal tracheal end. Then, beginning at the distal tracheal transection site, the surgeon removes segments of four to six tracheal cartilages from the ventral aspect of the tracheal wall, while preserving as much mucosa as possible (Figure 26-20). At the most proximal aspect of the proposed stoma, the dorsal tracheal membrane is apposed directly to the skin with simple interrupted sutures. Excess skin is excised as necessary to prevent skinfolds at the site, and then the skin is sutured directly to the peritracheal fascia and annular ligaments with intradermal sutures. The tracheostoma is completed by apposing the tracheal mucosa at the lateral and distal cartilage margins to the skin with simple continuous sutures (Figure 26-21).
 

Postoperative Care

Patients that have undergone permanent tracheostomy are monitored in the intensive care unit for 24 to 48 hours after surgery to observe for dyspnea and to care for the tracheostoma. Obstruction of the tracheostoma can result in death by asphyxiation. The stoma is inspected every 1 to 3 hours. The stoma is cleaned aseptically when mucus begins to occlude the tracheostoma or when respiratory effort increases. Mucus accumulating around the tracheostoma is carefully removed with moistened gauze sponges or cotton tipped applicators. Mucus accumulating in the tracheal lumen is removed with a moistened sterile cotton swab or suction tip. Cleaning must be performed carefully to avoid disrupting the suture line or irritating the tracheal mucosa. A water-impermeable ointment (petrolatum or boric acid ointment) or cyanoacrylate skin protectant is applied around the tracheostoma to discourage tracheal secretions from adhering and crusting. Low humidity during the first four to six days seems to reduce the amount of exudation and also promotes healing.

Initially, most animals secrete a moderate amount of mucus, with cleaning needed every 1 to 3 hours, but the interval gradually increases to every 4 to 6 hours by 7 days and twice daily by 30 days after surgery.^3,4 Patients are usually ready for discharge within 7 days of surgery; at this time, the stomas should be inspected every 4 to 6 hours and mucus removed as needed. Animals with severe tracheal irritation, secretory diseases, or those exposed to mucosal irritants (smoke, fragrances, dust, pollens, etc) may require more frequent cleaning. Most animals learn to expel mucus forcefully from their stoma in a self-cleaning manner. Hair is clipped from around the tracheostoma once or twice a month to prevent matting with mucus. Exercise and housing should be limited to clean areas free of smoke and unnecessary fragrances. Swimming is prohibited, and the stoma should be protected when sprays are used near the pet.

Owners are usually satisfied with their pet’s response after permanent tracheostomy.^3,4 Most pets have improved breathing, less noisy breathing, and increased activity. Approximately 60% of dogs and cats with permanent tracheostomy (without laryngectomy) lose their ability to vocalize normally.

Complications of permanent tracheostomy include stomal occlusion by skinfolds or mucus, dehiscence, and stenosis.^3,4,6-7 Skinfold occlusion is the most common long-term complication. It may be intermittent, related to the animal’s posture or continuous. Skinfold problems can be minimized by carefully assessing and excising larger amounts of skin from animals with loose skin folds during initial permanent tracheostomy surgery. Adhesions created by skin-peritracheal sutures are important in preventing skin fold problems. When skinfolds do interfere with tracheostomal airflow, skin lateral and dorsal to the stoma is excised without disturbing the mucosa-to-skin junction. Obstruction of the stoma by mucus is prevented by diligent patient observation and management. Dehiscence occurs if there is tension or irritation at the mucosa-to-skin junction.^4,6 It is prevented by using good surgical and management techniques. Dehiscence leads to a greater degree of stomal stenosis. Some stenosis occurs at all tracheostomal sites but it may progress to nearly complete stomal obstruction with dehiscence or trauma. If dyspnea recurs secondary to stenosis, it may be necessary to revise the tracheostoma surgically. Revision is best accomplished by making a skin incision from each corner of the stoma, removing an appropriate segment of skin and advancing the skin flap laterally.to evert the mucocuteanous junction thus widening the stoma (Figure 26-22).

Mortality associated with kinking of the trachea is likely (57%) to occur if the tracheostoma is created below the twelfth cartilage.⁶ Defense mechanisms in the bronchi, bronchioles, and lungs are adequate in most cases to prevent pulmonary infections in animals with permanent tracheostomies. Permanent tracheostomy does not affect breathing pattern or reflexes.⁷
 

References

1. Hedlund CS, Tangner CH, Montgomery DL, et al: A procedure for permanent tracheostomy and its effects on tracheal mucosa. Vet Surg 11:13, 1982.
2. Dalgard DW, Marshall PM, Fitzgerald GH, et al: Surgical technique for permanent tracheostomy in Beagle dogs. Lab Anim Sci 29: 367, 1979.
3. Hedlund CS: Tracheostomies in the management of canine and feline upper respiratory disease. Vet Clin North Am Small Anim Pract 24:873, 1994.
4. Hedlund CS, Tangner CH, Waldron DR, et al: Permanent tracheostomy: Perioperative and long-term data from 34 cases. J Am Anim Hosp Assoc 24:585, 1988.
5. Block G, Clarke K, Salisbury SK, et al: Total laryngectomy and permanent tracheostomy for treatment of laryngeal rhabdomyosarcoma in a dog. J Am Anim Hosp Assoc 31:510-513, 1995.
6. Dahm JD, Paniello C: Tracheostomy for long-term laryngeal experimentation. Otolaryngol Head Neck Surg 118:376-380, 1998.
7. Mutoh T, Kanamaru A, Suzuki H, et al: Effects of permanent tracheostomy on respiratory reflexes to lung inflation and casaicin in sevoflurane anaesthetized dogs. J Vet Med A 46:335-343, 1999.