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Application of Two Different Tracheal Stents in Small Toy Dogs with Tracheal Collapse
Zhenglin Piao, Young-Ung Kim, Jin-Su Kang, Dong-Bin Lee, Su-Young Heo and Nam-Soo Kim1
BK 21 Plus Program and College of Veterinary Medicine, Chonbuk National University, Iksan 54596, Korea (Received: August 13, 2019 / Accepted: October 11, 2019)
Abstacts : Tracheal collapse is a common respiratory disease in dogs. There are many ways to treat tracheal collapse, one of which is the use of an intraluminal stent. In this study, we divided 21 dogs into two groups and implant conventional stents and new nitinol stents. Comparison of two groups was based on following, feature of stent fracture, form of stent migration, clinical sign improvement, complication and prognosis. Approaching was established via C- arm under spontaneous breathing and placing a stent at the site of collapse. Using radiographic images, determine stent size accurately. For a comparison of identical condition, all intraluminal stents were placed 10 mm caudal from larynx to 10 mm cranial from carina. In this study, new nitinol stents improve the problems of conventional stents and may be effective in the treatment of tracheal collapse in small dogs.
Key words : intraluminal stent, nitinol, tracheal collapse, C-arm, dog.
Introduction
Canine tracheal collapse is a chronic wasting disease caused by relaxation of tracheal cartilage followed by weakening of tracheal cartilage which leads to decrease in tracheal diame- ter of cervical or thoracic portion by negative pressure during respiration (2,8,12,17). The cause of tracheal collapse can be explained by lacking production of collagen matrix contents because it causes decreased structural stability of the annular cartilage structure due to the abnormal function of chondro- cytes (14). Clinical signs of tracheal collapse include cough, respiratory distress, goose honking sound, exercise intoler- ance and cyanosis (2,12).
For diagnosing tracheal collapse precisely, additional exam- ination including tracheal endoscopy, fluoroscope, CT and MRI is required. However, it is reported that radiographic imaging is useful for diagnosis in local hospital and the accu- racy of diagnosis is about 60-90% (9,17). The severity of the disease is classified into grade 1 to grade 4, with 25%, 50%, 75%, and 100% collapse, respectively (16).
Small breeds, especially Yorkshire terrier, Poodle, Pomera- nian and Chihuahua and brachycephalic breeds including Pug and Pekinese are known to have disease predisposition (2,8).
Treatment of tracheal collapse includes medical treatment via recommended medications and surgical treatments. How- ever, the surgical technique is rather invasive as well as diffi- cult to approach and prolonged operating time is needed.
Thus intraluminal stabilization is preferred nowadays due to its rapidness, safety probability and possible discharge right after the treatment. Intraluminal stents so far have multiple
advantages with dramatic improvement of clinical signs.
In this study, comparative evaluation of the effect and prog- nosis of conventional stent and improved new stent after plac- ing each stents under C-arm in case of small breed dog tracheal collapse is shown.
Materials and Methods
Case selection
In this study, subjects were 21 small breed dogs with severe (grade 3-4) clinical sign of tracheal collapse with an average age of 11.6 and mean body weight of 3.6 kg. Amino- phylline (10 mg/kg) was prescribed for a 1 year for medical therapy, showing substantially decreased response to treat- ment. The study was divided in to two groups, group 1 were 13 dogs with conventional stent application and group 2 were 8 dogs with improved new nitinol stent application.
Group 1, conventional stent applied, had small breed dogs with an average age of 13.1 and mean body weight of 3.75 kg.
Among them, subjects with cervical tracheal collapse had mean grade of 3.5 meanwhile subjects with thoracic tracheal collapse had mean grade of 2.5.
Group 2, new nitinol stent applied, had small breed dogs with an average age of 9.1 and mean body weight of 3.4 kg.
Both subjects with cervical and thoracic tracheal collapse had a mean grade of 3.
Surgical procedure
Comparison of two groups was based on following, fea- ture of stent fracture, form of stent migration, clinical sign improvement, complication and prognosis. For a com- parison of identical condition, all intraluminal stents were placed 10 mm caudal from larynx to 10 mm cranial from carina.
1Corresponding author.
E-mail : [email protected]
Confirm tracheal collapse via radiographic images, inspira- tion and expiration respectively in small breed dogs with clinical signs consist with tracheal collapse. Then, aggregate radiographic image results and clinical signs and determine the severity of tracheal collapse.
Preoperative oxygen therapy and symptomatic treatment were prescribed to improve clinical signs. For a smooth pro- cedure, give propofol (6 mg/kg) for anesthesia. Approaching was established via C-arm under spontaneous breathing and placing a stent at the site of collapse. Using radiographic images, determine stent size accurately (Fig 1).
Implantation
All procedures applied on both group 1 and group 2 were under identical condition. C-arm was used in every proce- dure. Using C-arm image, insert stent until the tip of the guide and adjust the stents to make sure its end is place 10 mm cranial to carina.
Using C-arm, confirm the intraluminal stent is in its posi- tion without alteration and slowly expand the intraluminal stent for fixation. The position of the stent was confirmed
through C-arm and radiographs (Fig 2-4).
Stent selection
Group 1 used conventional stent, which is a human hepa- tobiliary stent. Group 2 used new stent, which was improved and specialized for animals. Nitinol was used in the new stent to gain extra strength as well as hook and closs type was combined to gain better flexibility (Fig 5-7). The old stents were attached only to the collapsed part of the trachea, but the new stents were improved on the principle that they cover the entire trachea.
Fig 1. Radiographic images of case 8 lateral view and ventro- dorsal view. In this image, stent length and diameter were cal- culated. Stent length was calculated in lateral view image from 10 mm caudal to larynx to 10 mm cranial to carina. Stent diam- eter was calculated from (mean tracheal diameter [l/l] + [d/
v]) × 2 ÷ 3.14. Mean tracheal diameter was calculated from nor- mal trachea diameter in lateral view and dorso-ventral view, respectively.
Fig 2. Preoperative image and postoperative image under the fluoroscopy (C-arm) of case 12.
Fig 3. Postoperative radiographic image of conventional stent of case 2.
Fig 4. Postoperative radiographic image of new nitinol stent of case 11.
Results
Observations were made in the intensive care unit for 24 hours after placement, and continuous oxygen supply and drug therapy were performed. Stent fracture, stent location, clinical symptoms, and complications were assessed using imaging equipment for comparison between group 1 and group 2.
In group 1, the survival period after insertion of 13 stents with old stent was between 1 month and 24 months. Three of the 13 dogs died within 6 months of placing the stent, 7 of the 10 surviving survived from 6 to 12 months, and 3 sur- vived for more than a year. Four stents were replaced due to
fracture, localization, and inflammation. Three of the four died within six months. Eight out of 13 animals with an old stent showed cough and inflammation of the trachea, requir- ing long term inflammation treatment. Among the 13 cases, stent fracture occurred in 4 cases and showed 30% stent frac- ture incidence (Fig 8). 3 out of 4 stent fractures, stents were reapplied. Among the 13 cases, stent migration occurred in 3 cases and showed 23% stent migration incidence (Fig 9). 2 out of 3 stent migrations, stents were reapplied. Inflamma- tion was occurred mostly from mild inflammation to severe inflammation after stent implantation. In particular, 6 out of 13 animals had severe inflammation and had an incidence of approximately 40%.
In group 2, the survival time after stent placement was in between 1 to 36 month in 8 dogs of with new stent. Within 2 month after placement of the stent, 1 out of 8 dogs died (40 days after the procedure), 3 out of 7 survived from 6 to 18 Fig 5. Comparison of stent for tracheal collapse (A: conventional stent, B: new nitinolstent).
Fig 6. Comparison of stent for tracheal collapse (A: conven- tional stent, B: new nitinol stent).
Fig 7. Comparison of stent for tracheal collapse (A: conven- tional stent – asymmetric structure, B: new nitinol stent – sym- metric).
Fig 8. Radiographic image of conventional stent fracture of case 8.
Fig 9. Radiographic image of conventional stent migration of case 5.
months, and 4 survived for more than 2 years. There was no fracture of the stent in 8 animals so far, but only 1 dog had the stent repositioned due to the movement and inflamma- tion reaction, which died within 6 months. The new stent showed inflammation similar to that of the old stent. 4 out of 8 patients had cough and inflammation of the trachea and treated for prolonged inflammation. No stent fracture in 8 animals so far. 1 out of 8 dogs showed a stent migration, incidence rate of 12.5%. The one with stent migration had under gone stent replacement. Inflammation was similar to that of group 1, which showed mostly mild inflammation to severe inflamma- tion after stent implantation. In particular, 3 out of 8 animals had severe inflammation and the incidence rate was about 37%, which was slightly lower than that in group 1.
Discussion
The procedure of intraluminal stent implantation is easier than that of external tracheal reconstruction and it can be eas- ily applied clinically because it can avoid nerve and vascular damage. The internal stents used in animals initially used bil- iary stents, which were used in human beings, but several problems were found and clinical veterinarians were restricted in their use (5,8).
Therefore, an improved stent is required and more sophis- ticated animal-specific intraluminal stents was developed. The conventional stent was made without consideration of move- ment or bending due to the placement of the site in the bile duct. Such a stent may inevitably cause fracture. Therefore, the need for improved stents has increased, and recently stents made of super-elastic materials such as nitinol, an alloy of nickel and titanium, have emerged (5). These materials can resist up to 10% without deformation and have thermo- formed memory and super-elastic properties. Advantages of intraluminal stents include non-invasive placement of the stent in the neck or thorax, with short anesthesia time, imme- diate improvement of clinical signs associated with tracheal collapse (12,18). However, it has disadvantages such as stent fracture, stent migration, tracheitis, obstruction of the stent lumen due to granulation tissue, and complication such as tracheal rupture. Therefore, this study was divided into two groups, conventional stents in group 1 and new nitinol stents for animal in group 2.
Stent fracture is the most serious complication after place- ment of the intraluminal stent. It is known that treatment should be started immediately after the stent fracture is con- firmed by radiographs (2,6,16). In the present study, stent fracture occurred in 4 out of 13 dogs in group 1, with a 30%
incidence. However, it was found that the performance of the stent was improved because the fracture did not occur in group 2.
In addition, the movement of the stent after placement has caused many side effects. However, in this study, the inci- dence of stent migration was 23% in group 1 and 12.5% in group 2 indicating that the performance of the new nitinol stent was improved. Excessive granulation tissue that often occurs after stent placement in the trachea can develop into severe tracheitis, and it is known that the incidence is 60% in humans (16-18). In this study, both groups 1 and 2 occurred
in a wide range from mild bronchitis to severe pneumonia.
This inflammatory response can be controlled by the use of anti-inflammatory drugs. In this study, corticosteroids, ami- nophylline and antibiotics were also administered (4,16).
The new nitinol stent used in this study is an animal stent that is made in Korea. This stent, which is specialized for dogs compared to conventional stents, is a nitinol stent char- acterized by minimal shortening, minimum mobility, high flexibility, low axial force and optimal radius. Group 2 with new nitinol stents showed better performance than group 1 with conventional stent.
The most important factor in the success of stent implanta- tion in the trachea is known as the implantation site (3,7,15).
Therefore, in this study, the new nitinol stent was attached to the whole of the trachea, and the placement was fixed. Anal- ysis of the results of this study showed that the improvement of clinical symptoms and prognosis were better than that of the stents attached to specific parts of the trachea. This result is very similar to the results of some researchers with the results being obtained from 10 mm caudal to larynx to 10 mm cranial to carina (1,10,11).
The new nitinol stents have been shown to greatly improve side effects such as stent fracture or stent migration, which is related to the increased compressive strength of the stent due to the use of nitinol (2,13,16). The cough caused by the for- eign body reaction due to the stent implantation gives strong stress to the wall of the trachea. It is known that the condi- tion to withstand this force is strong compressive force. In addition, selection of the appropriate length and width of the stent can accommodate irregularity of the lumen as well as the inherent expansion force of the stent, thereby maximiz- ing the contact of the intramural mucosa. Therefore, in this study, we selected the appropriate stent by measuring the width and length of the airway in 21 dogs. Particularly, the stent used in group 2 is an improved stent of an animal tra- chea-specific, and nitinol is used to increase the compressive strength of the stent and also known to maximize flexibility by combining hook and closs type (8,14,16).
Conclusion
The results of direct comparison between conventional intraluminal stents and new intraluminal stents in small breed dog tracheal collapse were as follows. The placement site of the intraluminal stents is appropriate from 10 mm caudal to larynx to 10 mm cranial to carina.
In case of the stent fracture, improved new nitinol stents were refined by 30% compared to conventional stents. New nitinol stents showed 10.5% improvement compared to con- ventional stents in stent migration. There was no difference between conventional stent and new nitinol stent in gross inflammation after the procedure. Therefore, improved new nitinol stent is more effective for the treatment of tracheal collapse in small breed dogs.
Acknowledgement
This research was supported by Chonbuk National University and M.I. Tech. Co..
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