Tracheal collapse (TC) is a progressive, degenerative condition predominantly observed in middle-aged to older small breed dogs (5,7,14,19,20). It is characterized by a weakening and flattening of the tracheal cartilage rings, leading to a decrease in tracheal diameter in the cervical or thoracic portions due to negative pressure during respiration (3,7,11,19). This condition results in clinical signs ranging from a characteristic “goose honking“ cough to severe respiratory distress (3).

TC is particularly prevalent in certain small breeds, including Yorkshire Terriers, Pomeranians, and Chihuahuas (3,7,11). The condition’s multifactorial etiology includes congenital factors, such as cartilage malformation or weakness, and acquired factors like chronic respiratory disease or obesity (1).

The diagnosis of TC is typically based on a combination of clinical signs and radiographic, fluoroscopic, or endoscopic evaluation. Radiographic imaging can be used for diagnosis in local hospitals, with diagnostic accuracy reported to be between 60-90% (9,19).

Initial management strategies for TC often focus on conservative measures, including weight management, cough suppressants, and corticosteroids. However, for dogs that do not respond adequately to medical management, or in cases of severe respiratory compromise, surgical intervention may be required (18). While surgical treatments have been shown to immediately improve clinical symptoms, serious postoperative complications, such as tracheal lacerations and laryngeal paralysis, have frequently been reported with extratracheal procedures. Consequently, endoluminal stenting therapy has emerged as the preferred technique (2-4,15,16). The primary indications for tracheal stent placement in dogs include severe tracheal collapse unresponsive to medical management, tracheal stenosis due to various causes, intraluminal or extraluminal neoplasia causing airway obstruction, tracheal compression by external structures, and management of traumatic tracheal injuries, particularly when surgical correction is not feasible or immediate airway patency is required (18).

An advanced therapeutic option for managing TC is the placement of an intraluminal tracheal stent. This minimally invasive procedure involves inserting a self-expanding mesh stent within the trachea to provide structural support and prevent further collapse. The advantages of intraluminal stents include non-invasive placement through the neck or thorax, short anesthesia duration, and immediate improvement in the clinical signs of TC (11,21). However, while this approach can lead to rapid and significant symptom relief, it is also associated with potential complications, such as stent migration, fracture, and the development of granulation tissue (1,12,17,18).

Despite the increasing application of tracheal stents in veterinary medicine, there remains a need for comprehensive studies that evaluate long-term outcomes and identify factors influencing success and complication rates. This thesis addresses this gap by retrospectively analyzing the outcomes of tracheal stent placements in 31 dogs treated at Smart Animal Hospital from 2018 to 2023. This study aims to evaluate the median follow-up time (MFT), clinical outcomes, and factors associated with success and complications following tracheal stent placement in dogs with tracheal collapse.

Study design and population

This study analyzed data from 31 dogs that underwent intraluminal placement of self-expanding nitinol stents for the treatment of tracheal collapse. The procedures were performed between January 2018 and November 2023. Follow-up time was defined as the period from the day of stent placement to the last contact, the date of death, or December 31, 2023, for the surviving dogs. Data on complications, procedural outcomes, and MFT were collected and analyzed. The outcomes were subjectively categorized into three levels based on post-procedural clinical improvement or complications, with complications being specifically defined and analyzed as stent-related. The outcomes were classified as follows: a “Good“ outcome was defined as the absence of dyspnea, infrequent coughing, and no complications; a “Fair“ outcome was characterized by frequent issues managed with medication or stent complications without clinical signs; and a “Poor“ outcome was assigned to patients with persistent problems unmanageable by medication or severe clinical signs due to stent complications. The classification criteria were based on previous study (13). MFT was estimated using the Kaplan-Meier survival curve.

Stent sizing and placement

Stent size was determined based on tracheal dimensions measured from X-ray, and CT images taken under positive pressure ventilation. The stent diameter chosen was 10-20% larger than the maximum tracheal diameter (Fig. 1). The length was measured from 10 mm behind the cricoid cartilage to 10 mm in front of the carina, as the appropriate placement site for intraluminal stents is from 10 mm caudal to the larynx to 10 mm cranial to the carina (Fig. 2) (11).

Figure 1. The stent diameter was determined based on tracheal dimensions measured from CT images taken under positive pressure ventilation, with the stent diameter chosen to be 10-20% larger than the maximum diameter measured in the cervical trachea.

Figure 2. The length was measured from X-ray images, spanning from 10 mm behind the cricoid cartilage to 10 mm in front of the carina, as the appropriate placement site for intraluminal stents is from 10 mm caudal to the larynx to 10 mm cranial to the carina.

Tracheal stent placement in dogs typically involved fluoroscopic-guided insertion of a self-expanding metallic stent. The procedure was performed under general anesthesia, with the patient in lateral recumbency. Anesthesia was maintained with propofol (Propofol-MCT; Daewon Pharmaceutical Co., South Korea). Following tracheal measurement and stent size selection, the delivery system was advanced through an endotracheal tube. The stent was then deployed under C-arm (KMC-650C; Komed Medical Co., South Korea) guidance, ensuring proper positioning across the affected tracheal segment. In cases where a suitably sized stent for the entire trachea was unavailable, the focus was on covering segments with severe collapse. Two types of stents were used: Infiniti stents (Vet Stent-Trachea^TM, Infiniti Medical, USA) in 19 dogs, and MI Tech stents (FAUNA STENT^TM, MI Tech, Korea) in 12 dogs.

Postoperative care

Postoperative management focused on reducing tracheal edema and stabilizing the stent using cough suppressants, steroids, antibiotics, and sedatives as required. Postoperative care included the administration of medications for 4-8 weeks depending on the patient’s condition: amoxicillin-clavulanate (Amocla; Kunwha Pharmaceutical Co., South Korea) (12.5 mg/kg PO BID), doxycycline (Doxycycline; Young Poong Pharmaceutical Co., South Korea) (5 mg/kg PO BID), bromhexine hydrochloride (Bromhexine HCl; Shinil Pharmaceutical Co., South Korea) (1 mg/kg PO BID), maropitant (Cerenia; Zoetis, USA) (1 mg/kg PO SID), omeprazole (Omed; SK Chemicals, South Korea) (1 mg/kg PO SID), codeine (Cofu; Yuhan Corporation, South Korea) (0.5 mg/kg PO BID), and aminophylline (Aminophylline; Daewon Pharmaceutical Co., South Korea) (11 mg/kg PO BID). Prednisolone (Solondo; Yuhan Corporation, South Korea) was tapered over 4 weeks, starting at 0.5 mg/kg PO BID.

Statistical analyses

Statistical analysis was performed using Fisher’s exact test and Kaplan-Meier survival curves (IBM SPSS statistics version 28, IBM Corp., Armonk, NY, USA). Fisher’s exact test was used to assess whether breed, gender, age, and weight had an impact on the outcome. A p-value greater than 0.05 was considered indicative of no significant association between these variables and the outcome.

To evaluate prognostic factors affecting survival, Kaplan-Meier survival curves were used to analyze the influence of bronchial collapse, stent complications, and age at the time of the procedure on survival rates. We assessed the presence of bronchial collapse using CT images. The evaluation was conducted by comparing CT images taken during both inspiration and expiration phases to determine the presence of bronchial collapse. The statistical significance of the survival curves was determined using the Tarone-Ware test.

The average follow-up time was 592 days, ranging from 35 to 2,189 days. As of December 31, 2023, of the 31 dogs, 11 were alive, 10 had died, and 10 were lost to follow-up. Excluding those lost to follow-up, the shortest post-procedure survival was 54 days, and the longest was 2,189 days. Three survived less than 6 months, one survived between 6 and 12 months, and 16 survived over a year, indicating that 80% of the dogs lived more than a year post-procedure (Table 1).

Table 1 . Clinical and demographic data of 31 dogs undergoing tracheal stent placement.

No	Breed	Age (year)	Sex	BW (kg)	Concurrent disease	Respiratory	Stent	Follow-up time (day)	Prognosis	Outcome
1	Pomeranian	7	MC	4.5	Soft palate elongation		Infiniti medical	2,189	Alive	Good
2	Maltese	12.2	MC	4	Bronchial collapse		Infiniti medical	705	Died	Good
3	Yorkshire terrier	7	MC	4.2	Bronchial collapse		Infiniti medical	301	Alive	Fair
4	Yorkshire terrier	4	IF	2.7	Soft palate elongation		Infiniti medical	2,057	Alive	Fair
5	Yorkshire terrier	8.3	IF	2	Bronchial collapse		Infiniti medical	1,961	Alive	Good
6	Silky terrier	9	MC	7	Bronchial collapse		Infiniti medical	263	Alive	Good
7	Yorkshire terrier	16	IM	1.7	-		Infiniti medical	67	Alive	Fair
8	Yorkshire terrier	5	MC	3.5	-		Infiniti medical	763	Died	Poor
9	Pomeranian	5	SF	2.7	Soft palate elongation, Bronchial collapse		Infiniti medical	1,608	Alive	Good
10	Yorkshire terrier	12.2	MC	3.7	Soft palate elongation, Bronchial collapse		Infiniti medical	1,526	Alive	Fair
11	Yorkshire terrier	12	SF	5	Soft palate elongation, Bronchial collapse		Infiniti medical	61	Alive	Good
12	Yorkshire terrier	13.4	SF	2.7	Bronchial collapse		Infiniti medical	638	Died	Poor
13	Chihuahua	9	SF	2.6	-		Infiniti medical	653	Died	Fair
14	Yorkshire terrier	6	IF	2.1	Bronchial collapse		Infiniti medical	221	Died	Good
15	Yorkshire terrier	10.3	MC	3.2	Bronchial collapse		Infiniti medical	44	Alive	Good
16	Yorkshire terrier	18	MC	3.3	Bronchial collapse		Infiniti medical	168	Died	Good
17	Yorkshire terrier	10.5	IM	2.9	Bronchial collapse		MI tech	533	Alive	Good
18	Pomeranian	12	MC	4	Bronchial collapse		MI tech	161	Alive	Fair
19	Yorkshire terrier	10.1	SF	2.3	Bronchial collapse		Infiniti medical	851	Died	Good
20	Yorkshire terrier	7.6	MC	2.8	Soft palate elongation, Bronchial collapse		MI tech	525	Died	Poor
21	Pomeranian	6.9	MC	2.6	Bronchial collapse		MI tech	117	Died	Poor
22	Pomeranian	8.7	MC	4	Soft palate elongation, Bronchial collapse		MI tech	817	Alive	Poor
23	Pomeranian	10.3	SF	3.1	Soft palate elongation, Bronchial collapse		MI tech	563	Alive	Good
24	Pomeranian	11	SF	4	Soft palate elongation, Bronchial collapse, Laryngeal collapse		MI tech	54	Died	Fair
25	Yorkshire terrier	13	MC	3	Bronchial collapse		Infiniti medical	38	Alive	Fair
26	Yorkshire terrier	11.8	MC	3.2	Soft palate elongation, Bronchial collapse		Infiniti medical	35	Alive	Good
27	Yorkshire terrier	10	MC	2.1	Bronchial collapse		MI tech	461	Alive	Fair
28	Pomeranian	10.7	MC	4	Soft palate elongation, Bronchial collapse		MI tech	411	Alive	Good
29	Chihuahua	6.6	MC	2	Bronchial collapse		MI tech	310	Alive	Good
30	Pomeranian	7.6	MC	4.2	Bronchial collapse		MI tech	219	Alive	Good
31	Pomeranian	13	MC	3.2	Soft palate elongation, Bronchial collapse		MI tech	45	Alive	Fair

MC, male castrated; SF, female spayed; IM, intact male; IF, intact female..

Yorkshire Terriers were the most common breed (17 out of 31), followed by Pomeranians (10), Chihuahuas (2), Maltese (1), and a Silky Terrier (1), reflecting the breed predisposition for tracheal collapse. The average age at the time of stent placement was around 9 years, with a general body weight of approximately 3 kg. Of the dogs, 21 were male and 10 were female, suggesting a higher incidence in males (Table 1), although current research indicates no known gender predisposition for the condition (3,19,20).

The dogs were categorized by age at the time of the procedure: the largest group was 7-11 years old (16 dogs), followed by those over 12 years old (9 dogs), and 2-6 years old (6 dogs) (Table 2). The MFT showed no significant statistical difference across the age groups, suggesting that age at the time of stent placement is not a critical factor in survival outcomes (Fig. 3).

Figure 3. Kaplan-Meier follow-up curves of 31 dogs comparing dogs in age 2-6 (n = 6), age 7-11 (n = 16), age ≥ 12 (n = 9) group (p-value = 0.65).

Table 2 . Age distribution and clinical outcomes of dogs with undergoing tracheal stent placement.

Age (year)	Number of patients	Outcome			Mean follow-up time (day)	Median follow-up time (estimated day)
		Good	Fair	Poor
≤1 (juvenile)	0	-	-	-	-	-
2-6 (mature adult)	6 (19.3%)	3 (50%)	1 (16.6%)	2 (33.3%)	846 (117-2,057)	763
7-11 (senior)	16 (51.6%)	10 (62.5%)	4 (25%)	2 (12.5%)	617.5 (35-2,189)	851
≥12 (geriatric)	9 (29%)	3 (33.3%)	5 (55.5%)	1 (11.1%)	378.7 (38-1,526)	638
Total	31	16 (51.6%)	10 (32.2%)	5 (16.1%)	592.4 (35-2,189)

The postoperative outcomes were classified into three categories. Sixteen dogs (51.6%) showed no dyspnea, had infrequent coughing, and experienced no complications, and were therefore categorized as having a “Good“ outcome. Ten dogs (32.2%) had frequent issues managed with medication or experienced stent complications without clinical signs, leading to a “Fair“ outcome. Lastly, five dogs (16.1%) had persistent problems unmanageable by medication or exhibited severe clinical signs due to stent complications, resulting in a “Poor“ outcome (Table 2).

Among the patients, 77% (24 dogs) did not experience stent-related complications, whereas seven dogs did, with complications including stent fracture, malposition, and migration (Table 3). Notably, the MFT was not significantly different between those with and without complications (Fig. 4).

Figure 4. Kaplan-Meier follow-up curves of 31 dogs comparing dogs without complication (n = 24) and dogs with complication (n = 7) (p-value = 0.32).

Table 3 . Postoperative complications in dogs with undergoing tracheal stent placement.

		Number of patients	Mean follow-up time (day)	Median follow-up time (estimated day)
No complication		24	624 (35-2,189)	851
Complications	Stent fracture	4	610.2 (461-817)	638
	Stent malposition	3	315.6 (67-763)
	Stent migration	1	638
	Granulation tissue formation	0	-

The majority of the dogs (26 out of 31) had concurrent bronchial collapse (Table 4). The analysis suggested a possible correlation between the presence of bronchial collapse and the occurrence of certain complications, such as stent fracture and migration. However, no significant differences in MFT were observed between the patients with and without bronchial collapse (Fig. 5).

Figure 5. Kaplan-Meier follow-up curves of 31 dogs comparing dogs without BC (n = 5), and dogs with BC (n = 26) (p-value = 0.44). BC, bronchial collapse.

Table 4 . Impact of comorbid bronchial collapse on tracheal stent outcomes.

	Number of patients	Outcome			Mean follow-up time (day)	Median follow-up time (estimated day)
		Good	Fair	Poor
No BC	5 (16.1%)	1 (20%)	3 (60%)	1 (20%)	1145.8 (67-2,189)	763
BC	26 (83.9%)	15 (57.6%)	7 (26.9%)	4 (15.3%)	486 (35-1,961)	851

BC, bronchial collapse..

We conducted a correlation analysis to evaluate whether breed, gender, age, and weight affected the outcomes. According to the results from Fisher’s exact test, breed, gender, age, and weight were found to have no significant association with the outcome (p > 0.05) (Table 5).

Table 5 . Correlation between outcome and various variables.

		Outcome			x2
		Good	Fair	Poor
Breed	Yorkshire Terrier	8 (25.8%)	6 (19.4%)	3 (9.7%)	1.000†
	Pomeranian	5 (16.1%)	3 (9.7%)	2 (6.5%)
	Others	3 (9.7%)	1 (3.2%)	0 (0.0%)
Sex	Male	10 (32.3%)	7 (22.6%)	4 (12.9%)	0.882†
	Female	6 (19.4%)	3 (9.7%)	1 (3.2%)
Age	<7	3 (9.7%)	1 (3.2%)	2 (6.5%)	0.393†
	7-12	10 (32.3%)	4 (12.9%)	2 (6.5%)
	≥12	3 (9.7%)	5 (16.1%)	1 (3.2%)
Weight	≤3 kg	6 (19.4%)	5 (16.1%)	3 (9.7%)	0.699†
	>3 kg	10 (32.3%)	5 (16.1%)	2 (6.5%)

^†Fisher’s exact test..

The average follow-up time of 592 days highlights the need for the long-term monitoring of dogs undergoing tracheal stent placement. The follow-up times, ranging from 35 days to over 6 years, underscore the variability in individual responses and emphasize the importance of continued monitoring and care. Moreover, the survival data, showing that 80% of the dogs (excluding those lost to follow-up) survived more than a year post-procedure, suggest that tracheal stenting can be a viable long-term solution for managing tracheal collapse.

One concern with stent placement is the need for anesthesia, particularly in patients with unstable respiration. However, no anesthesia-related issues were observed, irrespective of the age at which the procedure was performed. Although no significant correlation was found between the age at stent placement and MFT, further research could explore how the timing of stent placement post-initial diagnosis or symptom onset affects outcomes.

The classification of postoperative outcomes into “Good,“ “Fair,“ and “Poor“ provides a clear framework for evaluating the success of the procedure. Furthermore, the finding that over half of the dogs experienced a “Good“ outcome, with minimal to no complications, is promising. However, the 16.1% of dogs with “Poor“ outcomes highlight the need for improved management strategies for patients experiencing severe complications.

The observed complications, including stent fracture, malposition, and migration, are consistent with findings reported in the existing literature (11,13). The lack of significant impact on MFT indicates that, while these complications are serious, they can often be managed effectively without substantially affecting overall survival outcomes.

The high prevalence of concurrent bronchial collapse (83.9%) and its correlation with complications such as stent fracture and migration is a significant finding. It suggests that bronchial collapse may exacerbate the challenges associated with tracheal stenting and should be a key consideration in both the planning and post-operative management of TC. Despite these associations, the absence of significant differences in MFT between the patients with and without bronchial collapse indicates that the presence of bronchial collapse does not necessarily reduce overall survival time post-stenting.

When comparing the success rates and complications of surgical treatments for tracheal collapse to tracheal stenting, both approaches show similar rates of clinical improvement but differ in their complication profiles and invasiveness. Surgical treatments, primarily extraluminal ring prostheses, have reported success rates of 75-85%, with most dogs showing improvement in clinical signs (3,8). However, postoperative complication rates vary widely, ranging from 5-50%, and include serious issues such as tracheal lacerations, laryngeal paralysis, and persistent coughing (2,4). Tracheal stenting, as demonstrated in our study and supported by previous research, offers a less invasive alternative with comparable success rates. Previous studies have reported clinical improvement in 75-90% of cases following stent placement (10). Our findings of 51.6% ’Good’ and 32.2% ’Fair’ outcomes (totaling 83.9% improvement) align with these earlier reports. However, stent-related complications remain a concern, with reported rates between 23-42% (6,10). Our study’s complication rate of 23% falls at the lower end of this range. Common complications include stent fracture, migration, and excessive granulation tissue formation (6,17). While both methods offer similar levels of clinical improvement, stenting provides the advantages of being less invasive and offering immediate symptom relief. However, it may require long-term management of stent-related complications.

The retrospective nature of this study introduces several limitations, including non-standardized patient information and variable follow-up durations. The assessment of complications was not isolated to their individual effects, as some patients experienced multiple issues concurrently. Additionally, the subjective classification of outcomes may have introduced potential bias. The limited sample size and the lack of consideration for the specific causes of death in the deceased patients further limit the study’s conclusions. This study did not consider other underlying diseases, and thus, the potential impact of comorbidities on the outcomes and prognosis remains unaddressed. Furthermore, since not all patients received stents from the same manufacturer, the potential impact of the manufacturer’s difference cannot be overlooked. However, due to the difference in follow-up periods between the two manufacturers, we were unable to evaluate the effect of the manufacturer on the results in this study.

In conclusion, this study demonstrates that tracheal stent placement can provide substantial long-term benefits for dogs with tracheal collapse, particularly in certain small breeds predisposed to the condition. Although complications are not uncommon, they can often be managed without substantially impacting overall survival, and while the presence of concurrent bronchial collapse poses additional challenges, it does not necessarily reduce survival time. Overall, these findings underscore the importance of individualized patient assessment and the need for ongoing post-operative care to maximize the benefits of tracheal stenting in dogs.

Further studies with larger sample sizes and multi-center collaborations could provide more comprehensive data to validate these findings and improve the management strategies for tracheal collapse in dogs.

This research was funded by the Rural Development Administration, South Korea (grant number: RS-2023-00231965).

The authors have no conflicting interests.