Introduction

Tracheal collapse, a degenerative disorder of primarily toy dog breeds, leads to diminished airway caliber and a spectrum of clinical signs ranging from cough to respiratory distress.^1,2 Screening by thoracic radiography is common, although definitive diagnosis may require dynamic evaluation via fluoroscopy or direct visualization using tracheobronchoscopy.^3,4 In other cases, a presumptive diagnosis is made on the basis of clinical signs and signalment. Traditionally, tracheal collapse has been described as an isolated respiratory disorder in dogs.⁵ More recently, an increasing body of literature documents its occurrence with multiple other cardiopulmonary diseases.^6–11 These diseases share clinical signs, with no sign pathognomonic for any one disease, thus increasing the diagnostic challenge. Relevant comorbidities previously described include other types of airway collapse, chronic bronchitis, bronchiectasis, myxomatous mitral valve disease (MMVD), congestive heart failure (CHF), and pulmonary hypertension (PHT).^6–8,10,11 In the authors’ opinion, knowledge of these comorbidities is critical to developing a comprehensive diagnostic and therapeutic plan and providing an accurate prognosis.

Despite the frequency with which tracheal collapse is encountered in practice, no consensus exists regarding ideal diagnostic evaluation and therapeutic management of stable dogs. General guidelines, such as review articles or textbook chapters,^12–16 represent individual approaches and opinions, but no data from a larger number of experts exist. Only 2 studies describe dogs’ disease course treated medically rather than with stenting or surgery,^17,18 and 36% to 50% of dogs deteriorated over the observation period (mean observation period was 936 and 365 days, respectively). As dogs often become refractory to initial management, additional information on therapeutic approaches could provide valuable alternatives for poorly controlled disease in an attempt to prolong the period of effective medical management before interventional procedures or euthanasia. Furthermore, there is a paucity of information on specific details of diagnostic and therapeutic decisions, ancillary testing for and frequency of comorbid disorders, or goals for treatment outcomes. Understanding specialists’ perceptions of the importance of investigating the presence of these comorbidities, whether they perform the advanced diagnostic testing to identify them, and the perceived frequency with which they encounter them could help streamline diagnostic approaches for tracheal collapse.

The goal of this survey-based study was to describe specialists’ standard of care for the diagnosis and medical management of canine tracheal collapse. A secondary aim was to evaluate perceptions of the incidence of comorbid disorders and the ancillary diagnostics performed to that end. While some diagnostic and management practices were speculated to be evidence-based, it was also anticipated that there would be portions for which common practice is not supported by the literature or that have yet to be investigated prospectively.

Materials and Methods

Results

Comorbidities and ancillary diagnostics

Overall, respondents frequently considered it important to rule out the listed comorbidities in dogs with tracheal collapse (Figure 1). Respondents perceived that chronic bronchitis, bronchomalacia, and MMVD were the most commonly diagnosed comorbid disorders from the list provided (Figure 2). Ancillary diagnostic tests performed to detect comorbidities included airway sampling, parasite testing including for heartworms, sedated upper airway/laryngeal examinations, and echocardiograms. Almost half (46%) of respondents usually or always sampled airways, and all but one performed cytology and/or aerobic bacterial culture when they did. Other common tests on airway samples included Mycoplasma spp PCR (performed by 104 [63%] of all respondents that perform airway sampling) and anaerobic culture (81 [45%] respondents). Few respondents (13%) reported performing infectious disease PCR on airway samples, including a commercial respiratory PCR panel, Bordetella bronchiseptica PCR, and Angiostronglyus vasorum PCR. Almost half (44%) of respondents performed a sedated airway or laryngeal function exam either usually or always, but 36% (29 respondents) of those never administered doxapram hydrochloride in these evaluations. Over a third (37%) of respondents tested for respiratory parasites or heartworms either usually or always, and around a quarter (27%) reported performing an echocardiogram either usually or always.

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Bar charts illustrating the percentage of respondents ranking chronic bronchitis, bronchomalacia, bronchiectasis, pulmonary hypertension, myxomatous mitral valve disease, or congestive heart failure as extremely, very, somewhat, slightly, or not at all important to rule in or out in their diagnostic evaluation of a stable dog with cough and suspected tracheal collapse.

Citation: Journal of the American Veterinary Medical Association 261, 1; 10.2460/javma.22.03.0108

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Box-and-whisker plots showing surveyed specialists’ perceived prevalence (percentage of cases) of chronic bronchitis (CB), bronchomalacia, pulmonary hypertension (PHT), bronchiectasis, myxomatous mitral valve disease (MMVD), and congestive heart failure (CHF) diagnoses in stable dogs presenting for evaluation of tracheal collapse. The boxes indicate the interquartile range, and the circles indicate outliers.

Citation: Journal of the American Veterinary Medical Association 261, 1; 10.2460/javma.22.03.0108

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Medical management

Respondents were asked their current treatment preferences for outpatient medical management of a stable dog with canine tracheal collapse based on their prescribing habits over the last 12 months (Figure 3). Opioids were the most prescribed therapeutic with moderate agreement among respondents, being utilized by 78% for most or all dogs. The opioid prescribed most frequently was hydrocodone (56% [100/179]), followed by codeine (24%), butorphanol (10%), diphenoxylate (9%), or another not listed (2%). Forty percent (n = 72) of respondents intended that opioid medication would be given indefinitely, 56% anticipated that opioids would be used intermittently on the basis of need as perceived by the owner, and 4% expected opioids would be discontinued for most dogs.

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Bar charts illustrating the frequency with which surveyed specialists recalled prescribed varying classes of drugs to stable, coughing dogs diagnosed with tracheal collapse over the previous year.

Citation: Journal of the American Veterinary Medical Association 261, 1; 10.2460/javma.22.03.0108

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Nonopioid cough medications (cough suppressants and mucoactive agents) were used by 13% (22/180) of respondents in most or all cases, 43% some of the time, and 35% rarely or never. For respondents utilizing these alternative medications for cough (n = 138), the most used drug in this category was maropitant (55%), followed by dextromethorphan (17%), guaifenesin (9%), or bromhexine (7%).

Most (178/180) respondents also prescribed glucocorticoids, with 59% prescribing these always or most of the time over the previous 12 months. Of those prescribing glucocorticoids, 78% used prednisone or prednisolone most frequently and 21% used inhaled fluticasone most frequently. The most common prednisone or prednisolone starting dose was 1 mg/kg/d (69% of respondents), although 21% began treatment at 0.5 mg/kg/d. Respondents were divided over the anticipated length and duration of treatment, as follows: 50% (n = 89) foresaw that dogs would be continued indefinitely on a low maintenance dose, and 49% (87) used a tapering dose with the goal of discontinuing glucocorticoid treatment.

Anxiolytics or nonopioid sedatives were prescribed most often or always by 29% (53/180) of respondents. Of those who utilized these medications (n = 164), trazodone was the most popular choice for 64% of respondents, followed by acepromazine (15%), gabapentin (9%), diphenhydramine or another antihistamine (5%), alprazolam (4%), and clomipramine (2%). Respondents generally intended these drugs to be used intermittently (85%), although 12% intended discontinuation and 3% intended most of their dogs to take these indefinitely.

About one-quarter (26% [46/180]) of respondents prescribed bronchodilators most of the time or always. Of those utilizing bronchodilators, the most frequent choice was theophylline (69%), terbutaline (14%), albuterol (9%), aminophylline (3%), salmeterol (3%), or another type (1%).

Respondents (n = 180) variably prescribed antimicrobials for the treatment of tracheal collapse, most of the time or always (18%), sometimes (56%), or rarely or never (27%). For respondents prescribing antimicrobials (n = 166), the drug class selected most often was tetracyclines (67% of respondents), followed by penicillins (22%), macrolides (5%), and fluoroquinolones (4%). Zero respondents most commonly chose cephalosporins, and 1% of respondents most commonly chose an antibiotic class that was not listed. The survey did not discriminate between respondents who prescribed antimicrobials on the basis of clinical suspicion versus results of cytology or culture.

The treatment goals for medical management were control of severe clinical signs, and few aimed for complete resolution. While only 5% (10/176) of specialists aimed to control all coughing, > 95% aimed for absence of syncopal events, labored breathing, tachypnea, cyanosis, and an owner-perceived poor quality of life. Regarding other goals, 78% also aimed to diminish coughing during the night causing waking of the owner and 59% aimed for resolution of paroxysmal coughing.

Discussion

Despite a lack of standardized recommendations for the evaluation and management of dogs with tracheal collapse, our survey found some patterns of consistency among specialists in the diagnostic and therapeutic approach to stable dogs. Specifically, there is strong agreement on the use of thoracic radiographs in diagnosis and moderate agreement on the use of opioids in medical management. Survey respondents gave insight into the most common primary diagnostic and therapeutic modalities utilized by specialists for canine tracheal collapse. Additionally, this survey elucidated which of 6 common comorbidities are perceived as essential to investigate in evaluating a dog with suspected or confirmed tracheal collapse and the ancillary diagnostics or therapeutics used by practitioners to that end. Importantly, this survey identified 3 main areas of respondent diagnostic and therapeutic practices: those in which there is consensus between published literature and current practice, in which there exists a disparity between practice and scientific evidence, and that would benefit from future randomized controlled clinical trials due to a lack of evidence to support one practice over another.

In diagnosing tracheal collapse, respondents used static cervical and thoracic radiography most commonly, with a minority reporting a preference for dynamic inspiratory/expiratory radiography. This practice aligns with evidence that standard radiography is a valuable screening tool for tracheal collapse, with a sensitivity of 70% compared to tracheobronchoscopy as the gold standard.³ Despite its lack of favor with respondents, several studies have shown a benefit to obtaining at least a single lateral expiratory view, as that phase of respiration is most likely to highlight intrathoracic tracheal collapse.^3,4 Radiographs also have the added benefit of visualization of the lung parenchyma, cardiovascular structures, and extrathoracic anatomy in assessing for comorbid disorders. While it is possible that respondents chose not to proceed with expiratory views if tracheal collapse was already documented, plain radiography may not accurately reflect the degree and location of collapse. It may also miss collapse in up to 8% of cases.⁴ Fluoroscopy addresses some of the limitations of radiography by dynamically evaluating collapse of the large airways but is often available only at very large referral centers or academic practices. Limited availability likely accounted for few specialists commonly utilizing fluoroscopy despite spontaneous or induced coughing during fluoroscopic examination having the highest specificity (87%) for tracheal collapse diagnosis compared to tracheobronchoscopy as the gold standard.³

Tracheobronchoscopy allows direct visualization of the airways including more distal bronchi not easily evaluated with fluoroscopy, is more widely available in specialty practice than fluoroscopy, and serves as the current gold standard for diagnosing airway collapse in veterinary medicine.³ All of these factors likely account for it being the second most utilized diagnostic reported in this survey. Of those respondents using tracheobronchoscopy, most performed the entire or part of the procedure without endotracheal intubation. However, 18% had dogs intubated usually or always, a practice that limits complete evaluation of the cervical trachea. Importantly, tracheobronchoscopy may limit identification of the extent of dynamic collapse of both the trachea and bronchi, as many dogs experience apnea or respiratory depression associated with general anesthesia. This limitation could be partly overcome by use of fluoroscopy or paired inspiratory and expiratory radiographs or CT scans.³ While a possible perceived drawback of tracheobronchoscopy is the need for general anesthesia, a recent study found a low risk of postprocedural morbidity or mortality in dogs with respiratory disease undergoing CT and bronchoalveolar lavage.²⁰ It is likely then that the ability to fully investigate comorbidities such as chronic bronchitis and bronchomalacia, among others, outweighs the procedural risk for many dogs.

In dogs with suspected and confirmed tracheal collapse, it is the opinion of the authors that knowledge of comorbid diseases is critical to providing an optimal therapeutic plan and accurate prognosis. We have shown here that, among the surveyed specialists, ancillary diagnostic tests most commonly utilized include functional upper airway examination, echocardiography, tracheobronchoscopy, and airway lavage. Although not every test would be expected to be performed on every patient, without at least considering these diagnostics, it is the opinion of the authors that comorbidities are almost certainly underestimated. Advanced diagnostics generally require referral to a specialist, so knowledge of specialists’ perceptions of how significant and how common these comorbidities are is relevant. In the current study, most specialists acknowledged the importance of identifying comorbid diseases in dogs with tracheal collapse, with 81% declaring it to be very or extremely important to rule out CHF, 68% declaring it to be very or extremely important to rule out PHT, and 67% declaring it to be very or extremely important to rule out chronic bronchitis and bronchomalacia. This was mirrored by many specialists stating they diagnosed chronic bronchitis, bronchomalacia, and MMVD in over 50% of dogs, and with bronchiectasis and PHT being less common and CHF being uncommon but critical to rule out definitively (Figure 2). Importantly, this represents the opinions of surveyed specialists and may not be reflective of the true percentages of dogs with these comorbidities, as answers could have been influenced by recall or recency bias. Based on this survey, there is not a consensus among specialists regarding what a uniform, comprehensive evaluation for primary disease and comorbid disorders entails in a dog with tracheal collapse.

One area in which clinical practice appears to differ from the scientific evidence relates to the technique for a functional upper airway examination. In further investigating comorbid disorders, while many respondents performed a functional upper airway examination, almost half (45%) of respondents never gave doxapram to stimulate respiration, which is necessary if no or weak inspiratory efforts are observed. Several studies have documented the need for respiratory stimulation to fully evaluate laryngeal function and differentiate dogs with laryngeal paralysis from those with normal function.^21,22

In general, specialists reported prescribing medications similar to those previously recommended,^15,23 although some differences were identified. The difference in treatment approaches likely reflects our incomplete understanding of the pathogenesis of clinical signs. Even once comorbidities have been diligently accounted for, a knowledge gap in the factors driving clinical signs and disease progression remains. For example, in this survey, 50% of specialists expected that most dogs would need indefinite glucocorticoid treatment. A histochemical study¹ of dogs with tracheal collapse has documented that this is a degenerative disorder without reported inflammatory changes. Thus, use of glucocorticoids as an anti-inflammatory medication indefinitely specifically to treat tracheal collapse appears without rationale, and there should be consideration of the negative effect of extended glucocorticoid use on tracheal cartilage. In addition to the potential for inducing cartilage degradation,²⁴ chronic glucocorticoid use is also problematic for dogs with tracheal collapse, as it confers a predisposition for obesity.²⁵ It is also possible that specialists might have attempted to treat dogs for comorbidities, such as chronic bronchitis, in the situation that a complete work-up was not performed to rule these out.

Aside from the consensus of opioid cough suppressors and some use of glucocorticoids, respondents demonstrated that additional strategies are being used to manage clinical cases. Maropitant has been described as an adjunctive antitussive for chronic bronchitis²⁶ but not yet published in treatment of tracheal collapse. Bronchodilators have been claimed to benefit dogs by altering pressure dynamics and reducing the tendency of intrathoracic airways to collapse.²⁷ Additionally, some bronchodilators such as theophylline, may have anti-inflammatory properties.²⁸ In a study²⁹ of 47 dogs with tracheal collapse treated with theophylline, cough scores improved. However, concurrent medical therapy and comorbidities, along with subtherapeutic theophylline serum concentrations, confounds interpretation. Bronchodilator use also presents an interesting conundrum and may induce side effects opposite to the goals of maintaining a quiet state, less likely to induce cough. Future studies documenting the value or harm of some routinely used treatments without direct benefit to collapsed airways, such as chronic glucocorticoid exposure, bronchodilators, or behavioral modification, might provide data to alter current practice.

The survey responses reported here defined several additional areas where a consensus for clinical practice lacked evidence-based justification, highlighting opportunities for future prospective studies. Tracheal collapse manifests with chronic cough, and respondents were asked to consider a stable dog being evaluated for the disease; thus, it was surprising that 18% of respondents reported using antimicrobials most of the time or always, contrary to published guidelines.^30,31 This is an important finding because the contribution of bacterial infection or inflammation to the pathogenesis and progression of tracheal collapse remains unclear. Infection has not been recognized in dogs with tracheal collapse on histologic examination.¹ Other studies have shown conflicting results with positive culture rates as low as 10% or as high as 83%.^9,23,32 It is unclear whether antimicrobial use was intended to address secondary bacterial tracheobronchitis or whether respondents perceived a high risk for bacterial pneumonia in their stable dogs. The perception of bacterial pneumonia as a comorbidity among dogs being evaluated for tracheal collapse was not investigated in this survey, as the authors of the study did not consider bacterial pneumonia to be a common comorbid disorder during development of the survey. Given the aforementioned conflicting studies^9,32 and the antibiotic use demonstrated here, this represents a critical area for future research and possible improvement in antimicrobial stewardship. The selection of antimicrobials should be targeted to the underlying site of infection, with consideration of the blood-bronchus barrier for dogs with tracheobronchitis. Penicillins do not penetrate respiratory secretions well,³³ so their use (22% of respondents using antimicrobials selected penicillins) in this study was of particular interest. However, even expert guidelines remain divided with regard to the use of penicillins in canine infectious respiratory disease complex, as while some B bronchiseptica isolates are susceptible, all mycoplasmas are resistant.³⁰

This study had several limitations, many of which are inherent to survey-based research. Limited options were given for the perceived incidence of comorbid disorders, and all comorbid disorders of concern may not have been accurately captured, including bacterial pneumonia and laryngeal dysfunction. Differing geographic locations and drug availability bias prescribing practices in the treatment of tracheal collapse, as does the availability of advanced diagnostic equipment such as fluoroscopy. As such, what respondents reported doing and using may not actually be what they feel would be best practices. The specialist respondents may not be representative of all specialists who manage tracheal collapse, as some groups such as surgeons were not included. The diversity in the types of specialists participating in the survey may bias the type/severity of tracheal collapse they see, thereby influencing survey responses. Thus, these findings may not be applicable to the general population of dogs with tracheal collapse presenting to primary care practices. To maximize the relevance to general practitioners, we selected the most common clinical presentation and asked participants to consider a stable dog that is suitable for outpatient treatment. However, bias is not completely excluded, as individual interpretation of this description could vary. In response to the Likert scale questions, individual interpretations of “rarely,” “sometimes,” or other choices could also differ, and ideally exact percentages (eg, rarely = 1% to 24%, sometimes = 25% to 59%, etc) would have been given instead. Additionally, there is likely some degree of conscious reaction bias among respondents and the degree to which they felt the need to respond in a particular manner to fit in with procedural norms, which cannot be fully eliminated. However, the wide range of answers and identification of areas in which practice diverges from recommendations and evidence lend credence to the idea that conscious reaction bias was limited in our survey as much as possible. Importantly, while this study represents the opinions of specialists based on their training and personal experience, due to the paucity of literature in some areas those opinions may not reflect scientifically validated practices. In addition, while we surveyed a diverse population of board-certified veterinarians residing in private and academic practice worldwide, our 180 respondents may not truly represent specialists treating tracheal collapse. Thus, the data presented here must be interpreted with some degree of caution in generalization. However, we believe that data showing the disparity between common practices and evidence-based medicine and areas in which any published evidence is lacking remain important despite this limitation.

The results of this survey illustrate the most common diagnostic and therapeutic choices of specialists managing this condition. It highlights important information about comorbidities that can be utilized by general practitioners to consider advanced diagnostic testing. In addition, it summarizes real-world treatments and treatment goals, which will help manage client expectations for this chronic condition. Our findings also provide a valuable background for developing future prospective studies evaluating the incidence of comorbid disorders with tracheal collapse, the utility of ancillary diagnostic tests, and the comparison of different treatment regimens in the medical management of the disease.

Supplementary Materials

Supplementary materials are posted online at the journal website: avmajournals.avma.org