At the time of writing, there have been no randomized controlled trials assessing the insertion methods, or clinical effectiveness, of metallic airway stents. The literature therefore comprises case series, expert reviews and consensus statements from groups of leading practitioners. Aspects of the practice of metallic airway stenting vary widely between practitioners and centers, and the lack of an established evidence base means that any advice offered about stent choice, patient selection, or deployment techniques will necessarily strike some readers as different or even wrong. I have tried, wherever possible, both to reflect the breadth of published practice but at the same time to keep discussion of different options appropriate and practical.

For the sake of brevity, I shall use terms such as “malignant central airway obstruction” to mean obstruction of the central airways caused by malignant disease, and “benign aerodigestive fistula” to mean one caused by benign disease. This shorthand is not intended to imply that such a fistula, for example, is benign in its effect upon the patient.

The principal indications for metallic stent insertion are malignant central airway obstruction and management of malignant aerodigestive fistulae. Metallic stents are also used by some practitioners for the management of airway anastomotic complications following lung transplantation.

A successful and appropriate metallic stent insertion depends upon the stent being the right treatment both for the lesion and for the patient. The bronchoscopist should consider the following questions (adapted from Lee, Kupeli and Mehta 2010):

Table 28.1 addresses the relative suitability of metallic airway stents in different situations. An example of an ideal patient for metallic stenting would be of good performance status but suffering from breathlessness on exertion, with inoperable non-small cell lung cancer that has relapsed after treatment (say) with chemotherapy and radiotherapy. The patient would have a short, 80% stenosis of the midportion of the left main bronchus, just passable with a 5-mm flexible bronchoscope, and patent distal airways. Such a patient would have symptoms likely to benefit from stenting and a paucity of effective alternative treatments. She would be fit for the procedure and have a favorable lesion with no complicating factors, such as a lobar take-off within the treatment segment. No book can describe precisely what treatment choice to make in any possible situation, but in general decisions regarding stent insertion are influenced by the balance of favorable vs. adverse elements concerning the lesion and the patient, and the presence or absence of effective, alternative treatment options. The patient’s life expectancy should neither be too short (futility, lack of meaningful palliation) nor too long (risk of fracture). Above all, stenting is a palliative procedure, and so the bronchoscopist should never have to persuade the patient to have a stent inserted. This last consideration is particularly important because some patients report few symptoms, even in the presence of apparently severe airway lesions. The temptation for the bronchoscopist is to intervene, especially if the airway lesion appears readily treatable. Caution is advised in such circumstances, however, because no risk is greater than the one that did not need to be taken.

The work-up for metallic stenting necessarily depends upon the patient’s condition. In emergent near-complete tracheal obstruction, intubation and immediate rigid bronchoscopy by the most experienced available practitioner without any pre-procedure work-up may be entirely appropriate. Almost always, however, in addition to a history and physical examination and standard pre-bronchoscopy tests, it is appropriate to request airway CT scanning, spirometry, a flow-volume loop, and an assessment of breathlessness, such as the MRC or Borg dyspnea scores. Some operators favor a prior flexible bronchoscopy to assess the lesion anatomy. Once these tests have been completed, it will often be possible to arrive at a complete specification for the desired stent. Airway CT scanning, particularly if carried out on a high-speed multidetector scanner, can be used to create multiplanar reformat and virtual bronchoscopy images. These enable the diameter of the stenosed segment and, if present, the adjacent normal airway to be estimated. Where the target bronchus has no segment of normal caliber throughout its length, estimates of its usual caliber can be obtained by measuring the corresponding contralateral airway. Images displayed on lung window settings provide a more accurate impression of the likely endobronchial appearances. Dynamic CT images, obtained during expiration, can further define regions where dynamic airway collapse occurs, sometimes as a consequence of the destruction of airway cartilage by underlying tumor. Standard flexible bronchoscopy provides visual assessment of the severity and length of airway stenoses, the patency of any adjacent lobar take-off (particularly the right upper lobe), and the presence or absence of endobronchial tumor. In addition, the relationship of the stenosed segment to distal or proximal airway branches can be precisely assessed. In lower-volume centers, performing a flexible bronchoscopy prior to stenting permits a stent of the required size to be ordered for the procedure, thereby minimizing the requirement to keep an extensive stock of stent sizes. For many straightforward cases, CT scanning, lung function, and clinical assessment will be sufficient to enable satisfactory treatment planning, with an on-table flexible bronchoscopy providing additional information and enabling final stent selection and sizing. This approach has the benefit of simplicity and economy but relies upon the availability of a full range of stent sizes and types, since the final selection is made during the procedure.

Miyazawa and colleagues assessed the impact of a more sophisticated pre-procedure assessment in patients with lung cancer requiring airway stenting. Dynamic airway CT scanning, flow-volume loops, endobronchial ultrasound (EBUS) and ultrathin flexible bronchoscopy were performed before and after stenting in 64 patients. These techniques were combined to allow the identification of specific choke points (wave-speed flow-limiting segments) within the airways. The CT scans were performed at end-expiration, with 3D airway reformats. Characteristic flow-volume loop appearances could be identified for lesions in three locations: the trachea, around the main carina, and confined to the main bronchi, with more complex stenoses exhibiting a combination of appearances. EBUS was used to assess the integrity of underlying airway cartilage. In some patients, this was found to have been destroyed by extrinsic tumor over a length of airway wall greater than that affected by the stenosis itself. EBUS allowed the authors to select longer stents in this situation, to prevent dynamic airway collapse of the damaged airway. Ultrathin bronchoscopy was employed to identify choke points directly. In this study, a combination of silicone and metallic stenting was employed. Using these pre-procedure assessments, patients with tracheal (n  =  20), carinal (n  =  16), and bronchial lesions (n  =  18) were satisfactorily treated with a single stent procedure alone, with significant improvements in lung function parameters and WHO dyspnea grade. In patients with complex stenoses affecting more than one region of the tracheobronchial tree, however, migration of the choke point after an initial stent procedure was observed. In this group of patients, even though significant improvements in lung function and dyspnea scores were observed after a single procedure, there was a further incremental and statistically significant improvement in each of these parameters after a second stent procedure, in which stent deployment was targeted at the migrated choke points identified by the detailed assessment described. The results of this study are worth emphasizing, because many bronchoscopists might have congratulated themselves after achieving the more modest patient benefits demonstrated after the first stent procedure in these complex lesions. This study provides evidence in favor of the proposition that all such patients should be treated in centers with access to a full range of advanced bronchoscopic techniques and that there is a lot more to successful stenting than knowing how to deploy the stent.