© 2004 American Thoracic Society
Airway Obstruction and StentingMore Complex than We Thought?Beth Israel Deaconess Medical Center Boston, Massachusetts Stenting the airways has now been an integral part of the medical armamentarium for more than a decade (1). Although the incidence and prevalence of symptomatic central airway obstruction remains unknown, the epidemiology of lung cancer suggests that an increasing number of patients will suffer from this condition. An estimated 20 to 30% of patients with lung cancer will experience complications associated with airway obstruction, such as dyspnea, pneumonia, and atelectasis (2). Especially for malignancy-related, symptomatic airway obstruction, placing an airway prosthesis has been considered to be one of the first line palliative interventions (3). The results of airway stenting, although generally positive, are varied. Follow-up after stenting is often inadequate, and several different clinical endpoints may be used to evaluate success. Measurements of pulmonary function after stenting have revealed variable outcomes (4, 5). We need, however, to optimize these outcomes because unrelieved airway obstruction can lead to intolerable symptoms, severely reducing quality of life, and, potentially, life expectancy. In the medical community, the discussion of stenting has centered on stent technology and which type of stent to use, rather than around the physiology of stented airways and how knowledge of that physiology can be used to improve results. In this issue of the Journal (pp. 1096–1102), Miyazawa and coworkers (6) report their results for 64 patients with cancer who received airway stents after unsuccessful balloon dilation. Only patients with extrinsic compression secondary to advanced malignancy were included, to avoid confounding by the interventions necessary to treat intrinsic obstruction. Patients were divided into four groups by the location of obstruction: tracheal, carinal, bronchial, or extensive (multiple-site) compression. Pulmonary function tests and computed tomography (CT) were performed before airway intervention and follow-up endoscopy. Patients underwent therapeutic bronchoscopy with an open ventilating scope; before stent placement, patients underwent endobronchial ultrasound, to evaluate the airway walls, as well as ultrathin bronchoscopy, to evaluate airway patency distal to the obstruction. Various stents were placed at the visualized flow-limiting segments after dilation. Follow-up included monthly endoscopy until death to identify stent complications and to assess airway patency. The authors found distinctive flow–volume loop patterns for each of the four obstruction locations. Almost all patients reported substantial improvement in dyspnea after stenting, and most flow–volume loops returned to normal. Interestingly, all 10 patients with extensive stenosis showed persisting choke points and showed only moderate improvement in dyspnea and spirometry measures. Repeat endoscopy was performed with the help of endobronchial ultrasound and ultrathin bronchoscopy. Endoscopy revealed that the choke points had migrated distally from the stented segments, and endobronchial ultrasound established that their presence was associated with the destruction of cartilage. Additional stenting at the choke points markedly improved dyspnea and pulmonary function; these results then equaled those of the other groups. Median survival ranged between 3 and 6 months, with patients in the extensive stenosis group having the shortest survival. No patient died of airway obstruction, and only minor stent complications were reported. On the basis of these results, the authors now evaluate all their patients with CT, endobronchial ultrasound and ultrathin bronchoscopy before stenting, and they assess choke points to guide the placement of stabilizing stents. This study raises several important issues. Airways are complex structures, and their continued patency depends on many factors, including the integrity of the airway walls. Additional imaging techniques, such as endobronchial ultrasound, have been believed for some time to contribute to the success of therapeutic endobronchial procedures (7). This is the first well controlled study to establish this success. Stenting, performed in skilled hands, was uniformly successful in preventing death from asphyxiation and in relieving dyspnea, results that constitute important improvements in this setting. There were no therapeutic failures if physiologic and imaging information was included in decision-making. Palliative outcomes in this experienced treatment center were excellent. The authors are to be commended for their meticulous data collection and extensive testing. It would be desirable if they could elaborate on certain aspects of their research. For example, the endobronchial imaging of patients who did not require additional stenting for choke-point migration is not described. It would be reassuring to know that the airway walls were intact in these patients. With that knowledge, we could act confidently on endobronchial ultrasound findings that indicated destruction of the supporting cartilage during the first endoscopy. Because the authors have extensive experience in this field, they are in a unique position to develop an algorithm to determine which tests are truly required. Multiple CT scans and different endoscopic studies may not be necessary. For example, modern, multiple-head CT scanning might replace the need for ultrathin endoscopy (8, 9). In this study, a single-head CT scan was used. It is desirable to minimize testing and to achieve maximum benefit when treating end-of-life problems so that quality of life can be maximized and expenses minimized. Costs are especially important here, considering that the group with the shortest survival benefited the most from the more extensive interventions. Overall, this study contributes substantially to our knowledge about airway obstruction and recanalization. Airway obstruction is a complex and dynamic problem. This complexity is not surprising, given the intricate airway wall structure and physiology, even in normal circumstances. To think of airway obstruction as simply a mechanical process, subject to a "quick fix" by stenting, may just not be enough to improve patient care or to advance our understanding of airway obstruction. FOOTNOTES Conflict of Interest Statement: A.E. has received research and educational grants from Olympus America and Boston Scientific. REFERENCES
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