Airway Stents - All You Need To Know

Introduction

An important cause of mortality and morbidity is obstruction of the trachea and the mainstem bronchi. Some diseases can bring about this condition. The actual prevalence and incidence of the condition is still unknown. However, the epidemiology of lung cancer indicates an increase in cases with complications of proximal endobronchial diseases (a tumor developing in the proximal part of the airway tubes). More research has been done in treating such patients due to the expansion of subspecialties like interventional pulmonology.

What Are Airway Stents?

Airway stents are endobronchial prostheses made of different materials that help to support and keep the hollow tubular parts of the airway open.

1. An airway stent can support the airway wall against a collapse or external compression.

2. Prevent the extension of the tumor into the airway.

3. Help manage fistulas in the airways.

4. Prevent the collapse of the airway tubes.

They are generally made using bio-compactible materials like medical-grade Silicone or Nickel-Titanium alloy.

What Are the Indications of an Airway Stent?

Many malignant and benign lesions may require the use of an airway stent. The surgeon or the interventional pulmonologist ensures that the patient has no airway disease that must be managed surgically before the placement of the stent, irrespective of the indication. In some cases, introducing an airway stent may complicate the surgery. Moreover, there may be inflammation and injury to the mucosa that may interfere with the healing. The common indications for airway stenting include:

1. Malignant Disease:

• Malignant airway obstruction.

• Tumor within the bronchi with residual obstruction.

• A mixture of endobronchial and extrinsic tumors.

• Support from cartilage is lost due to the tumor.

• Malignant esophagotracheal fistula (a pathological opening between the bronchi, trachea, and the esophagus).

2. Benign Conditions:

• Benign stricture or narrowing of the airway more than 4 cm.

• A benign stricture (narrowing of the airway) in a patient who can not be operated.

• Post-transplant airway stenosis

• Tracheo-bronchomalacia (a rare condition where the trachea is weak and soft).

• Benign esophago-tracheal fistula.

When Is an Airway Stent Contraindicated?

Airway stents are contraindicated or avoided in cases where there is a chance of other treatment options like surgery that help restore airway function. They can include:

• Patients can undergo surgical interventions to repair their malignant or benign causes of airway obstruction.

• Very severe impairment in the functioning of the airway.

• Very limited survival expectancy.

• No viable (living or healthy) lung tissue beyond the stenosis.

Relative contraindications can include:

• Patients who can tolerate general anesthesia or moderate sedation.

What Are the Types of Airway Stents?

An ideal stent is still in the process of development. According to a theory an ideal stent should be:

• Stable.

• Strong to be able to withhold excessive compressive forces that compromise the lumen patency.

• Biocompatible.

• Available in all required sizes.

• Should not move without requirement.

• Easily deployed.

• Act as a barrier to the tumor.

• Prevent the tumor from eluding the lumen space.

The type of stent used depends on the anatomy of the patient’s airway and the underlying conditions.

• Silicone Stent: These stents are easy to place and remove. They are well-tolerated and provide a good vault effect (able to move according to the tissue movement). They cause less granulation tissue (a part of the normal healing process) formation and can be customized based on bronchoscopy and Computerized Tomographic (CT) measurements. It provides less chance of tumor invasion and can be repositioned easily. However, it has an increased risk of migration. Some types of silicone stents have integrated studs on them to prevent migration. It has a higher risk of infection.

• Self-expandable Metallic Stents: These can be placed under flexible bronchoscopy (a small flexible tube with a camera inserted to view the various structures in the airway) and fluoroscopy (a procedure that can image real-time moving images of the human body). However, in cases where rigid bronchoscopy can be performed, it is considered safer as it provides an option to control obstructive or hemorrhagic complications quickly. It has a larger internal-to-external diameter ratio than a silicone stent. It is made of materials that are self-expanding devices that exert more force on the mucosa in the airways. It is difficult to move or reposition and has a higher risk of vascular perforation. High rates of tumor invasion and granulation tissue are other disadvantages.

• Hybrid Stents: These stents are made of more than one type of material. Hence, it harnesses the advantages and mitigates the disadvantages of each. However, I is more expensive than stents made of a single material.

What Are the Future Innovations in Airway Stents?

• Drug Eluting Stents: This could be a good option to prevent the formulation of granulation and malignant tissue. It is under research in gastrointestinal endoscopy with anti-cancer and anti-proliferative agents. A Cisplatin-eluding stent, which is biodegradable, is under research for the central airways. It is still required to be tested on humans.

• Biodegradable Airway Stents: These stents are still under research. It has been demonstrated successfully in six people with conditions that had a temporary requirement for the stent. However, four of the six people tested had a faster rate pf biodegradation. Hence, it requires more work and modifications.

• Customization of Conventional Stents: Research is in progress on the conventional stents, which can be customized using CT scan and bronchoscopy. The conventional stents are modified depending on the patient’s requirements.

• Patient-Specific Airway Stents: It is also called ‘Bespoke stents.’ A stent is customized using a CT scan could theoretically reduce the risk of migration, granulation tissue formation, and mucus plug. These aspects are still under research and need to be worked on.

Conclusion

Using an airway stent in a benign or malignant condition is an immediate relief of symptoms in most cases. Currently, the safety profile of silicone stents is more commendable than the others and, hence, is more commonly used. More research is being done in this field, which allows stents to have better facilities in the upcoming days, months, or years.