Central airway obstruction is often secondary to a variety of benign and malignant airway pathologies (Table 1). Its symptoms can occur suddenly (e.g. foreign body aspiration) or develop gradually (most malignant tumors in the airway), and in most cases it is easily misdiagnosed as asthma or chronic obstructive pulmonary disease and delayed diagnosis and treatment due to the lack of awareness of airway obstruction [1]. Han Zhihai, Department of Respiratory Medicine, Naval General Hospital
Interventional therapy is a good method to address central airway obstruction. The operation should be performed in a specialized operating room (with equipment) and by an experienced specialist. The patient’s condition and the interventional approach should be fully discussed by multidisciplinary physicians before the operation. The stability of the patient’s condition preoperatively, the prognostic requirements and the adequacy of the awareness of potential complications can also potentially influence the success of the procedure [2-5].
Table 1: Diseases causing airway obstruction
Primary malignant disease :
Non-malignant tumors.
Primary intra-airway malignancy
Lymph node enlargement
Bronchopulmonary carcinoma
Nodular disease
Cystic adenoid carcinoma of the trachea
Mucinous epidermis-like tumor
Carcinoid tumor
Infected lymph node enlargement
(e.g. tuberculosis)
Vascular tracts (sling)
Plasma cell malignancies
Cartilage lesions
Metastatic malignancies
Bronchopulmonary carcinoma
Breast cancer
Kidney Cancer
Thyroid Cancer
Bowel Cancer
Sarcoma
Melanoma
Recurrent polychondritis
Granulomatous tissue hyperplasia
Tracheal intubation
Tracheotomy
tracheal stent
foreign body
surgical anastomosis
Wegener’s granuloma
Laryngeal cancer
Esophageal cancer
Mediastinal tumor
Thymoma
Thyroid cancer
Teratoma
Lymph node enlargement
Invasion of lymph nodes by the above malignant tumors
Lymphoma
Pseudotumor
Malignant tumor
Amyloidosis
Papillomatous hyperplasia
Airway dynamic lesions
Tracheobronchial softening
Diffuse endotracheal lesions
Idiopathic
tuberculosis
tuberculosis
Other
Intrathoracic thyroid
Mucus plug
Vocal cord paralysis
Epiglottitis
blood clots
This article provides a review of the diagnosis and treatment of central airway obstruction in recent years as follows.
Diagnosis of central airway obstruction.
The functional manifestation of airway obstruction is a decrease in ventilation and oxygenation. Small airway obstructions are often asymptomatic due to minimal restriction of airflow. However, when infection is present in the airway, patients may also experience a sudden increase in symptoms due to edema of the lesion or an increase in secretions. It is not uncommon for patients with airway obstruction before this obstruction reaches a critical point to be misdiagnosed as an asthma attack or an acute exacerbation of COPD. Airway obstruction is also often misdiagnosed as pneumonia, so if a patient with pneumonia has not resolved in 6 weeks, a bronchoscopy must be performed to rule out airway obstruction.
When airflow restriction reaches a critical point, the patient will develop significant signs and symptoms. Most patients present with a persistent monotonous croup. High-pitched wheezing is a sign of subglottic or main airway obstruction, and the ensuing dyspnea often signals the onset of respiratory failure.
The progression of the patient’s disease depends on the nature and location of the primary lesion (e.g., endotracheal foreign bodies tend to be more acute in symptoms while intrathoracic thyroids tend to be slower, and main tracheal obstruction is more symptomatic while bronchial obstruction is less symptomatic). Prolonged tracheal intubation or incision also greatly increases the risk of tracheal stenosis or softening.
There have been many clinical studies devoted to the confirmation of central airway obstruction and its degree for a long time, and the following consensus has been reached.
1.Plain chest x-ray is difficult to confirm the diagnosis.
2. Plain CT lung examination can detect airway obstruction but with poor sensitivity. If airway obstruction is suspected and time allows, it is better to perform high-resolution CT with 3D reconstruction, which not only can confirm the diagnosis and distinguish the degree of obstruction, but also has important reference value for the next interventional treatment [6].
3. Pulmonary function tests: the characteristic flow-volume loop changes have important reference value for the diagnosis of airway obstruction [3-6].
(1) As shown in Figure 2, the flow-volume loop can reflect the condition of airway obstruction. The more severe the airway obstruction, the smaller the volume obtained for the same flow rate. Even in the absence of symptoms, a change in the flow-volume loop suggests an airway diameter of less than 8 mm.
(2) Figure 3 illustrates the shape of the flow-volume loop for different airway obstruction conditions. The left graph shows the lung function with a fixed obstructive lesion in the main airway, the middle graph is an extra-thoracic dynamic obstruction, so the inspiratory part of the flow-volume ring appears as a restriction graph, while the right graph is an intra-thoracic dynamic obstruction, so the graph is the opposite of the middle graph change and shows an expiratory part restriction.
(3) Flow-volume loop changes in main bronchial obstruction
Figures 4 and 5 demonstrate the flow-volume loops before and after treatment of complete unilateral main bronchial obstruction, suggesting a positive correlation between inspiratory and expiratory flow rate and volume and the diameter of the airway.
(4) Flow-volume rings of bronchial obstruction after stent placement showing the inspiratory phase with a tail.
(4) Of course, bronchoscopy is the gold standard for the diagnosis of tracheal obstruction. Usually, external pressure airway obstruction can only be clearly diagnosed by bronchoscopy.
Management of central airway obstruction.
The management of central airway obstruction is usually divided into two phases: the initial stabilization phase and the intra-airway intervention phase.
Initial stabilization phase: For a patient with stable disease, pulmonary imaging and pulmonary function tests must be performed. If the patient has severe airway obstruction and very poor lung function, measures must be taken to stabilize the condition to ensure safe ventilation and oxygenation during the intervention.
The preferred option is tracheal intubation. This is the best option for patients who are still breathing normally, although of course there may be some risk for some patients with poor respiratory function due to the need for about moderate anesthesia.
For patients with severe airway obstruction, the use of a rigid bronchoscope with ventilation is the preferred option for airway control. Rigid bronchoscopes not only provide adequate ventilation while observing, but also provide therapeutic function. In emergency situations, rigid bronchoscopes are also able to dilate the airway [7].
Bronchoscopy should be performed after the airway is secured and there is adequate gas exchange. Bronchoscopy allows observation of the airway and the lesion, biopsy of the lesion and aspiration of the distal secretions. The information obtained can be an important reference for further treatment, especially for the dilatation of the obstructed central airway. Again, it is important to note that endoscopic interventions must be performed by a team of trained and experienced specialists.
It is advisable to apply appropriate antibiotics after interventional treatment of airway obstruction. There is no evidence that empirical application of antibiotics after airway interventions is ineffective. Likewise, there is no evidence that hormones have a positive effect on reducing complications after treatment.
Airway interventions: After completion of endoscopy, evaluation and discussion of treatment options, further interventions can be performed. In recent years, there has been a significant increase in the number and methods of intra-airway interventions, and the choice of intervention should be carefully selected based on the patient’s condition. The combined application of multiple methods may be superior to airway dilation alone in terms of post-treatment airway secretion production and long-term outcomes [8].
Table 2: Effectiveness of various treatment methods on central airway obstruction
Operation name
Endotracheal lesion
External pressure lesion
Mixed lesions
Laser
+
–
+
Electrocoagulation
+
–
+
Freezing
+*
– –
+*
Brachytherapy (internal radiation)
+*
-*
+*
APC
+
–
+
Photodynamic
+*
– –
+*
Stent placement
–
+
+#
*: Contraindication when respiratory failure is expected to occur.
#: Indication: Intraluminal diameter of the tube is less than 50% of normal after intervention.
Rigid tracheoscopy is preferred when the patient is expected to have a high level of intra-airway bleeding and is unstable. Rigid bronchoscopy does not burn has also become the best choice for many endoscopic laser treatments. Of course, in most cases, fiberoptic bronchoscopy is still preferred due to ease of handling.
Foreign body removal: The incidence of foreign bodies in the trachea is much higher in children than in adults and can also lead to sudden and fatal airway obstruction. Available data show no difference between rigid bronchoscopy and fiberoptic bronchoscopy in the choice of foreign body removal.
Scleroscopy or balloon dilation: In emergency situations, scleroscopy or balloon dilation of the obstructed airway can be performed after general anesthesia. The patient is given adequate oxygen before the procedure, and the rigid scope can be passed through and remove the obstructing tissue to dilate the airway, but of course, both rigid scope and balloon dilation can squeeze the obstructing tissue to the edge of the trachea. There is not much bleeding during the procedure. Balloon dilation can be well performed by fiberoptic bronchoscopy [9].
Scleroscopy is also a good option in less urgent cases such as tracheal intubation that leads to airway narrowing. The advantages of scleroscopic treatment compared to balloon dilation are less mucosal damage and less secondary granulomatous growth after the procedure.
Balloon dilation can achieve immediate results for endotracheal tumors or external pressure strictures, but the disadvantage is that this effect is not long lasting. The granulation and tissue proliferation caused by mucosal destruction after treatment quickly cause restenosis. For this reason, balloon dilation is usually not performed alone and is often followed by laser treatment or stent placement [10-11].
Laser treatment: ND:YAG laser treatment is often performed under a rigid microscope or can be performed by an experienced endoscopist under a fiberoptic bronchoscope. The interaction of the tissue and the laser causes the removal of obstructive tissue from the airway. Indications for laser treatment are short airway obstructions with a visible distal lumen. This technique should mostly be used for tracheal stenosis due to malignant tumors in the lumen, after tracheal intubation or dissection. The procedure is effective in dilating the lumen with minimal bleeding. The disadvantage, as with balloon dilation, is the short duration [12-13].
Numerous studies have confirmed the safety of laser surgery performed by specialists. Complications include tracheal intubation, burning of the tissues in the airway, and cautery damage to the tracheoscope itself, with severe hypoxemia and even respiratory failure [14].
Electrocoagulation and APC: These treatments also rely on heat to destroy the tissues that obstruct the lumen. During electrocoagulation high-frequency currents can reach the tissue through a bipolar probe, generating heat that causes tissue necrosis.APC is a similar interventional treatment. Argon gas is ejected through a PTFE probe that passes through the tracheoscope to the tissue, where it is ionized by high-frequency currents and an electron arc, resulting in tissue necrosis without direct contact with the tissue. The treatment depth is approximately 2-3 mm, which makes APC a powerful tool for the treatment of tissue surface bleeding, smaller areas of granulation tissue and papillary tumors [15].
Photodynamic therapy: for those patients with intraductal tumors for which laser treatment is ineffective. Tumor tissues are injected with a photosensitizing substance and after a suitable period of time, these tissues are then subjected to non-thermal tissue necrosis with 630 nm laser irradiation. Because of the ability to infiltrate to a depth of 5-10 mm, photodynamic therapy is also suitable for patients with complete blockage of the lumen, where subsequent removal of necrotic material and clearance of secretions with fiberoptic bronchoscopy is necessary. A side effect of photodynamic therapy is that the treatment may cause photosensitization of the skin for up to 6 weeks [16-17].
Cryotherapy: in contrast to thermal treatments such as laser, cryotherapy relies on repeated freezing/heating cycles leading to tissue necrosis. Cryotherapy can be performed through fiberoptic bronchoscopy. Cryotherapy is much more time-consuming than laser treatment because of the repeated treatment and the need to repeatedly remove necrotic tissue [18-19].
Cryotherapy can be used in patients with complete tracheal occlusion, but it is not recommended for critically ill or emergency patients because of the delay in its therapeutic effect. For any patient whose intervention requires endotracheal intervention, a longer period of stability is necessary, and internal irradiation or stent placement can achieve this effect.
Extratracheal radiotherapy or endotracheal irradiation: Endotracheal irradiation is an easy to perform and effective treatment for patients with airway obstruction and has excellent post-treatment effects. Extratracheal irradiation may produce undesired radiation effects on normal tissues in the chest cavity, thus affecting gas exchange. Endotracheal irradiation does not have these disadvantages and can be used in patients with airway obstruction who have already undergone extratracheal irradiation [20].
After endotracheal interventions such as laser treatment in patients with airway obstruction, the internal irradiation guide tube can be placed through the tracheoscope to the site to be treated, and after reconfirming that the placement is correct, the radioactive material can be placed through the guide tube. Side effects of internal irradiation are rare (tracheobronchitis), but severe bleeding and fistula formation have been reported. The decision to place a stent after internal irradiation can be based on the patency of the airway [21-22].
Tracheal stenting: stenting can be considered after the airway obstruction has been opened by interventional treatment. Tracheal stenting is a good interventional option for extratracheal compression, persistent bronchopleural fistula or bronchoesophageal fistula. The first tracheal and bronchial stents were used in 1990, after which a large number of stents with various advantages and disadvantages have been used in clinical practice [23-27].
Silicone stents are not considered expensive and are usually placed via rigid bronchoscopy. Most metallic stents can be placed through a fiberoptic bronchoscope, but they are expensive, thus partially offsetting the benefits of such stents that can be performed without the operating room and under general anesthesia. There are several new stents made of composite materials, but their advantages and disadvantages are being further evaluated [28-32].
Tracheal stents are durable, but often require regular follow-up. Patients need to carry a card with the type and model of stent placed for follow-up. Stent placement is not a contraindication to tracheal intubation, but if the stent is placed in the main trachea, tracheal intubation is best performed under tracheoscopic guidance.
The initial follow-up after stent placement must be done carefully in order to avoid changes in position. Not only is it important to observe stent position during early follow-up, but selective management of reocclusion and granulation growth is also important. According to US regulations, the first follow-up after stent placement should be performed 6-8 weeks after the procedure, during which the position of the metal stent can be moved. This is followed by an endoscopic follow-up at 3-6 months and of course a review at any time if there is a problem with the stent.
Surgical resection: The indications for airway obstruction requiring surgical intervention are: severe, benign, and relatively short distance obstruction. Patient selection is more stringent, as the complications and mortality of surgery are often unacceptable to patients with localized obstruction.
Surgical treatment of patients with airway obstruction should be performed in experienced hospitals by experienced surgeons. The surgical procedure is often a sleeve resection and end-to-end anastomosis. Complications of surgery include restenosis of the anastomosis and the possible need for multiple interventional dilations, reoperations and permanent tracheal intubation. The incidence of these complications was 9% in a single-center report of 900 cases. In this report, risk factors for these complications included diabetes mellitus, history of tracheobronchial surgery, strictures longer than 4 cm and resection of the pharyngotrachea [33-36].
In the future, with the development of bioengineering techniques, bio-peritoneal membranes that can cover the surface of end-of-year tissues may emerge, and tracheal grafts, which are currently difficult to achieve due to less vascularity, may also be possible with the development of muscle flap reconstruction techniques [37-46].
In conclusion, central airway obstruction can be the result of compression within or outside the airway and can cause different symptoms ranging from shortness of breath to respiratory failure. In patients with ventilatory failure, swift establishment of ventilation to ensure oxygenation is of paramount importance.
The choice of the next airway intervention depends on the nature of the lesion, the characteristics of the intervention, and the estimation of the maintenance time. Usually, the best airway intervention is a combination of several methods that can be completed within the time allowed by the disease.
Follow-up is essential for interventions. Follow-up allows observation of the occurrence of complications and the effectiveness of the intervention. A comprehensive interventional approach is best done at an experienced center by an experienced multidisciplinary airway intervention specialist.
Balloon dilation/
Laser therapy
Electrocoagulation
APC