Tracheal Reconstruction Using a Nitinol Stent for Thoracic Tracheal Rupture

Abstract

Materials and Methods

A double-wire woven nitinol stent was handmade using a cross-and-hook knitting method. The fabricated endotracheal stent was 2-3 mm larger than the internal diameter of the ruptured trachea. The clinical signs and respiratory pattern, image diagnoses (radiography and computed tomography), and tracheoscopy results after endotracheal stenting were assessed for six months.

Results

The lateral cervical radiographs showed that the intratracheal stent was properly placed without migration or stent fracture at the insertion site. After two to three weeks of tracheal stenting, the coughing and dyspnea signs revolved, and the normal activities in all dogs were resumed.

Conclusion

The double-wire braided nitinol stent showed no migration or deformation in the canine trachea. These results suggest that the nitinol stent is compatible with the canine tracheal structure and has flexibility with an adequate radial force.

Introduction

The trachea provides a safe and sturdy pathway for air to travel from the larynx to the lungs. The canine trachea extends from the cricoid cartilage of the larynx to the carina and is composed of 35 to 45 rings. The trachea is a flexible tube with a sturdy C-shaped cartilage ring (1). The trachea consists of the tracheal muscles, C-shaped cartilage, a band of connective tissue that runs along the back of the trachea and connects the ends of the incomplete tracheal rings, and a mucous membrane that lines the lumen of the trachea (2).

Surgical treatment is required when tracheal stenosis, tumors, trauma, injuries, and congenital diseases obstruct the trachea. Endotracheal tube intubation refers to the placement of a tube extending from the oral cavity into the trachea. Endotracheal intubation involves administering inhaled anesthetics, ensuring an unconscious canine airway, and administering oxygen to assist ventilation. Intubation is also necessary when scaling and polishing in canine teeth to prevent aspiration pneumonia.

Canine tracheal injuries can be treated with supportive medical care or surgical intervention, depending on the dog’s clinical condition, the extent of the tracheal injury, and the cause of the tracheal disruption. A tracheal rupture can lead to severe morbidity and mortality in toy and miniature dogs. Proper monitoring of tracheal injuries requires a serial assessment of the respiratory status and progression of subcutaneous emphysema (3). Surgery is indicated if significant secondary side effects occur after medical management of a tracheal rupture to avoid the inevitable worsening of symptoms and death.

The authors previously reported that endotracheal stent support can prevent stenosis of the tracheal anastomosis site during tracheal tumor resection in small-breed dogs (1). In this study, the tracheas of miniature and toy dogs with a thoracic tracheal rupture and systemic subcutaneous emphysema were reconstructed with a double-wire woven nitinol stent. These dogs were referred for the treatment of a tracheal rupture and tracheal reconstruction caused by the failure to deflate the endotracheal tube cuff during postoperative extubation. Radiography, computed tomography (CT), and tracheoscopy are the best tools to diagnose this tracheal rupture. Treatment includes a combination of antitussives, bronchodilators, and antibiotics.

Materials and Methods

Canine patients. Two miniature and toy breed dogs complaining of dyspnea and exercise intolerance were referred to the Veterinary Teaching Hospital, Chungbuk National University. Veterinarians obtained the clinical history and findings and performed thoracic radiography and CT. These dogs had body temperatures above 38.8˚C and showed labored breathing, voice distortion, prolonged breath sounds, and chest pain. The Institutional Animal Care and Use Committee approved this study.

Fabrication of endotracheal nitinol stents. A double-wire woven nitinol stent was handmade using a cross-and-hook knitting method. This nitinol stent was a self-expanding endotracheal stent made from an alloy with the same atomic ratio of nickel and titanium. The radial force of the endotracheal stent was 268.4±4.2 gf, and the thickness of the stent wire was 117 µm. Radiopaque markers were attached to both ends and above and below the stent to confirm the location of the stent in the canine trachea. The stent size was selected by measuring the length and diameter of the damaged trachea site in a lateral chest radiograph. The endotracheal stent was fabricated 2-3 mm larger than the internal diameter of the ruptured trachea to minimize future shortening and migration.

Double-wire woven nitinol endotracheal stent insertion. The dogs were placed under anesthesia. The endotracheal stent was inserted, and therapeutic medications were administered as reported elsewhere (1). The dogs were treated with antitussives, bronchodilators, and antibiotics in the intensive care unit for seven to ten days. The dogs were sedated and restrained to reduce the risk of tracheal dehiscence. The dogs were given supplemental oxygen and closely monitored for clinical signs.

Radiological, CT, and tracheoscopic evaluations. Imaging and diagnostic procedures in dogs were performed as described elsewhere (1). All dogs underwent radiological, CT, and tracheoscopic evaluations at one to two week intervals. Tracheoscopy was used to observe the stented site directly and evaluate the healing status of the trachea. The tracheal wall at the stented site was examined using a tracheoscopy, but no tracheal tissue biopsies were performed.

Results

Clinical signs and auscultatory findings. The dogs showed auscultatory findings such as dyspnea, exercise intolerance, and thoracic pain upon admission, but cough and dyspnea improved within two to three weeks after tracheal stent insertion, and all dogs returned to normal activity.

Evaluation of radiographs, CT scans, and tracheoscopy. Radiographs and CT scans revealed air leakage from the thoracic trachea into the subcutaneous tissue, as well as subcutaneous emphysema and pneumomediastinum in the thoracic cavity (Figure 1). These tracheal ruptures were located at the lateral junction of the tracheal ring and tracheal muscle at the thoracic inlet (Figure 2), and the rupture site was similar to the length of the tracheal cuff. These dogs experienced accidental tracheal rupture during the process of extubating the endotracheal tube cuff after surgery. Endoscopy and lateral cervical radiographs showed no evidence of stent migration from the insertion site into the trachea or stent rupture (Figure 3).

Figure 1.

Radiograph showing a dog with subcutaneous emphysema (arrow) and pneumomediastinum caused by an air leak from the thoracic trachea.

Figure 2.

A computed tomography scan of the thoracic cavity, revealing a ruptured thoracic trachea (white arrow) and severe subcutaneous emphysema.

Figure 3.

Images of a canine tracheoscopy (A) and computed tomography scan (B) 10 weeks after the placement of an endotracheal stent (white arrows). Radiopaque markers were attached to both ends and above and below the stent to identify its location in the trachea (black arrows).

Discussion

The dogs with a thoracic tracheal rupture and severe, life-threatening injuries requiring surgical intervention were referred to Veterinary Teaching Hospital, Chungbuk National University. The radiographs and CT scans revealed generalized subcutaneous emphysema and pneumomediastinum due to thoracic tracheal rupture. Radiographs and CT scans of the head, neck, and chest identified changes consistent with tracheal injury.

Tracheal disruption is usually caused by excessive intubation or improper use of a stylet on the tracheal tube during intubation. The tracheal injuries also occur from overinflation of the tracheal tube cuff, repositioning the head without removing the tracheal tube, and removing the tracheal tube without deflating the cuff (4). In these cases, the trachea was ruptured because the tracheal tube was extubated after surgery without deflating the air in the cuff of the tracheal tube. In these dogs, a tracheal rupture was diagnosed due to longitudinal traction of the endotracheal tube.

Several studies have reported tracheal rupture due to endotracheal intubation in cats (3). Several studies have attempted to identify which type of endotracheal tube is most likely to cause tracheal rupture. In cats, the risk of tracheal rupture increases when the amount of air in the cuff exceeds the amount required to keep the endotracheal tube airtight in cats (5). Therefore, it has been suggested that low-pressure endotracheal tube cuffs are safer than high-pressure cuffs. Nevertheless, cases of tracheal rupture in dogs are rare. We report that removing intubation with an inflated cuff removes more intratracheal fluid than removing the cuff with a deflated cuff, which helps prevent aspiration when fluid is present in the proximal trachea (6). Effective inflation of the endotracheal tube cuff is necessary to avoid iatrogenic tracheal rupture. Proper use of the endotracheal tube and inflation of the cuff appears to be more important than the type of endotracheal tube used (3,5). The appropriate size of the endotracheal tube in dogs is 70% of the tracheal diameter measured on a thoracic radiograph (7).

The dogs in the present study were examined by radiography, CT scan, and tracheoscopy to confirm the location and extent of tracheal rupture. Surgery was then decided considering the clinical condition of the dog, the extent of tracheal damage, breathing pattern, and the progression of subcutaneous emphysema. Both literature data and the authors’ experience have shown that endotracheal stent insertion can be used to treat tracheal stenosis, tumors, and collapse (1,8). A previous study reported a tracheal tumor resection with an endotracheal stent placed at the tracheal anastomosis to prevent tracheal stenosis (1). Endotracheal stent placement is a minimally invasive method to treat a stenosed or obstructed tracheal lumen. The advantages of endotracheal stents include short operation and anesthesia times, minimally invasive insertion, and fewer complications (1,8). Nitinol is self-locking, self-expanding, and self-compressing, with excellent biocompatibility. Primary cytotoxicity and corrosion rate studies reported that nitinol did not reduce proliferation or inhibit growth of cells in contact with metal surfaces (1).

Some researchers reported side effects after stent insertion in dogs after long-term observations (9). The side effects include stent shortening, fracture, and stent migration when the internal diameter of the inserted stent is small. Therefore, a tracheal stent size 2-3 mm larger than the internal diameter of the trachea after dilation was selected to minimize stent shortening and migration. If a stent ruptures, a second stent that is longer than the first must be inserted over the first (10). Dogs with confirmed tracheal kinking and those with weight gain after stent placement are vulnerable to stent fracture, resulting in a poor prognosis (8).

In the present study, the endotracheal stent had been properly placed without movement or stent fracture at the insertion site on the lateral cervical radiographs. During the observation period, no dog showed evidence of endotracheal stenosis or tracheitis at the stent insertion site on tracheoscopy and CT after tracheal stent insertion. A stent that optimized the stent-to-lumen coordination was selected using the appropriate mechanical and physicochemical properties of nitinol.

Stented dogs should be treated continually with bronchodilators and anti-inflammatory drugs and undergo regular physical examinations and thoracic radiographs. Anti-inflammatory drugs should be administered because inflammatory or granular tissue growth within the stent can result in bacterial tracheitis or pneumonia, leading to rapid clinical deterioration (9).

Properly monitoring tracheal injuries requires a continuous assessment of the respiratory status and progression of subcutaneous emphysema (3). Thoracic radiographs of dogs with acute tracheal perforation may reveal pneumomediastinum due to air leaking from the tracheal rupture and dissection along the muscle to the thoracic inlet (11). Tracheal rupture must be repaired surgically, lest secondary subcutaneous emphysema and, ultimately, death occur (12).

Obesity in dogs increases the radial forces in the trachea, placing greater pressure on the stent supporting the tracheal lumen and significantly increasing the risk of recurrent respiratory symptoms (8). The tracheal ruptures in these dogs were reconstructed surgically, and the pneumothorax and subcutaneous emphysema were treated. The dogs recovered in the intensive care unit and were discharged after receiving antitussives, prednisone, and antibiotics. After stent insertion, the dogs were minimally active when delivered home, but their activity increased gradually over the following weeks. The coughing or dyspnea were resolved within two to three weeks after tracheal stent placement, and all dogs returned to normal activity. The stented dogs exhibited hoarseness and vocalization for two to five weeks. Generalized subcutaneous emphysema and pneumo-mediastinum in these dogs improved within four to six weeks (13). These results suggest that the double-woven wire stent conforms perfectly to the canine tracheal structure and the nitinol material within the trachea has minimal side effects.

Conflicts of Interest

The Authors declare no conflicts of interest in relation to this study.

Authors’ Contributions

This study was designed by Park and Choi. Park, Kim and Choi analyzed the diagnostic images and collected the data. All Authors have read and agreed to the published version of the manuscript.

Acknowledgements

This work was supported by the Korea Institute of Planning and Evaluation for Technology in Food, and Agriculture (322086-04), Republic of Korea.

Artificial Intelligence (AI) Disclosure

No artificial intelligence (AI) tools, including large language models or machine learning software, were used in the preparation, analysis, or presentation of this manuscript.