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* From the Department of Interventional Pulmonology (Dr. Wahidi), Division of Pulmonary and Critical Care Medicine, Duke University Medical Center, Durham, NC; the Department of Pulmonary and Critical Care Medicine (Dr. Herth), Thoraxklinik Heidelberg, Heidelberg, Germany; and the Department of Interventional Pulmonology (Dr. Ernst), Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA.
Correspondence to: Armin Ernst, MD, FCCP, Chief, Interventional Pulmonology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Ave, Boston, MA 02215; e-mail: aernst{at}bidmc.harvard.edu
Abstract
Interventional pulmonology (IP) provides comprehensive care to patients with structural airway disorders and pleural diseases. A growing armamentarium of diagnostic and therapeutic tools has expanded the interventional pulmonologist’s ability to care for pulmonary patients with complex abnormalities, often in concert and close collaboration with physicians in other specialties, such as thoracic surgery. Innovative technologies promise to have an impact on diseases and clinical entities not traditionally treated by invasive pulmonary interventions, such as asthma, COPD, and the solitary pulmonary nodule. Training, credentialing, reimbursement, and scientific validation remain key necessities for the continued growth of IP, and require a concerted effort by chest physicians and their professional organizations.
Key Words: airways • bronchoscopy • interventional pulmonology • pleural disease • procedures
Interventional pulmonology (IP) is an evolving field within pulmonary medicine that focuses on providing consultative and procedural services to patients with malignant and nonmalignant airway disorders and pleural diseases. The emergence of this discipline was fueled by the surge in technology geared toward lung health, and by the need to maintain procedural competency and expertise in an ever-expanding specialty of pulmonary and critical care medicine.
IP encompasses the following three main areas in pulmonary medicine: malignant and nonmalignant airway disorders; pleural diseases; and artificial airways. Additional activities may be included depending on the practice environment of the individual physician. The requisite skills range from simple thoracic ultrasound (US) to complex diagnostic endobronchial US (EBUS) and resection of large airway tumors (Table 1 ). With many innovations looming on the horizon, IP is extending to other lung diseases with therapies such as endoscopic lung volume reduction for emphysema and bronchial thermoplasty for asthma. In this review, we will summarize the current state of IP, emerging technologies, and future directions.
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Therapeutic Bronchoscopy
Therapeutic bronchoscopy was the nidus for the growth of the IP field. The introduction of laser technology into the tracheobronchial tree and the advent of airway stents in the early 1990s sparked an interest among pulmonologists to gain more experience in the diagnosis and management of airway disorders, and caused a resurgence of rigid bronchoscopy (RB).
The main indication for therapeutic bronchoscopy is the presence of airway disorders resulting in central airway obstruction (CAO) [ie, trachea, mainstem bronchi, and bronchus intermedius] where the relief of blockage will have the greatest symptomatic benefits.1 The etiologies of CAO include malignant airway disorders (eg, primary bronchogenic carcinoma and metastatic malignancy to the bronchi) and nonmalignant airway disorders (eg, sarcoidosis, amyloidosis, relapsing polychondritis, infectious complications of tuberculosis, histoplasmosis or coccidioidomycosis, complications of lung transplantation, and sequelae from the introduction of artificial airways). The airway compromise may remain asymptomatic until a critical airway diameter (ie, 5 to 8 mm) is reached or a new event (eg, infection, bleeding, or mucus plugging) exacerbates the underlying stenosis. The most common symptoms include dyspnea and cough; hemoptysis may be prominent in patients with malignancies, while infectious symptoms surface when postobstructive pneumonia develops. The diagnosis of CAO depends on a thorough history and physical examination (with findings such as ipsilateral wheezing, stridor, or localized crackles), imaging studies (eg, chest radiograph and chest CT scan), and diagnostic bronchoscopy.2
Advances in bronchoscopic tools and techniques have provided interventional pulmonologists with a wide array of therapeutic options that can be used individually or in combination to match the needs of all patients. RB has seen a resurgence in the last 2 decades3 (Fig 1 ). After being the only tool to access the airway for almost an entire century, RB faded with the introduction of flexible bronchoscopy in the late 1960s. The renewed interest stemmed from the recognition of the advantages of RB, such as the ability to ventilate the patient while intervening in the airways, the capability of using large-suction catheters to aspirate blood or debris, and the utility of the barrel of the rigid bronchoscope in "coring out" tumor tissue and dilating stenoses.
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Dilatation of airway stenoses can be achieved with controlled insertion of the barrel of the rigid bronchoscope, the sequential introduction of serially enlarging semi-rigid (Jackson) dilators, or balloon dilatation.45 The latter is considered the preferred method given its perceived gentle dilatation and minimal trauma to the airways.
Tissue removal is a main objective in the relief of airway obstruction. The abnormal tissue can be caused by tumor growth, inflammatory process, or necrotic debris.
Mechanical debridement is accomplished by coring out the tissue with the barrel of the rigid bronchoscope or by grasping large pieces with rigid forceps. A new instrument is the so-called therapeutic flexible bronchoscope, which has a large working channel (3.2 mm) and can accommodate large flexible forceps, making it feasible to remove medium-sized endobronchial tissue growths during flexible bronchoscopy procedures in selected patients. During RB, a variety of flexible bronchoscopes are routinely used to access angulated or distal airways and to facilitate the debridement process in these locations.
Tumor destruction can also be accomplished with a variety of endobronchial tools including heat therapy (eg, laser therapy, electrocautery, argon plasma coagulation), photodynamic therapy, cryotherapy, or radiotherapy (brachytherapy)6789101112131415 [Table 2 62636465666768697071727374].
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With the availability of effective local therapy for the airway, the paradigm of primary treatment in patients with malignant airway obstruction is shifting from external beam radiation to therapeutic bronchoscopy. External beam radiation was the treatment of choice for patients with CAO, but its effects were often delayed and unreliable. The success rate for reestablishing the aeration of atelectatic lung portions has ranged from 21 to 23%.1819 If IP capabilities are available, first-line endoscopic interventions should now be strongly considered due to more immediate results and a favorable safety profile. Radiation therapy can then often be performed in a stable patient with an improved performance status to consolidate the effect of endoscopic therapy.
The body of evidence supporting the effectiveness of therapeutic bronchoscopy, while growing, is still limited. The data have come predominantly from retrospective studies with very few comparative or randomized clinical trials. The data for ablative therapy is summarized in Table 1. Similar to ablative therapy, airway stenting achieves symptomatic relief in the majority of patients (metal stents, 82 to 97%17202122; silicone stents, 85 to 95%1623).
The impact on survival has been more difficult to elucidate due to the uncontrolled nature and small size of most studies. Clearly, more research is needed to address questions pertaining to the comparison of the effects of various therapeutic modalities, the role of combined therapy, and maximizing benefit while reducing risk.
Diagnostic Bronchoscopy
The following two US Food and Drug Administration-approved innovations in diagnostic bronchoscopy are available to the interventional pulmonologist: autofluorescence bronchoscopy (AFB) and EBUS. Both modalities provide the following information that is beyond the vision of conventional white-light bronchoscopy: premalignant or early malignant mucosal transformation with AFB; and structural characteristics of the airway wall and adjacent tissue with EBUS. It is arguable that both technologies can be performed by noninterventional pulmonologists, but the steep learning curve and the high cost of equipment make a dedicated practice of IP the ideal venue.
The autofluorescence bronchoscope emits a specific wavelength of light, collects the tissue-reflected light, and projects it onto a screen, with green color representing a normal autofluorescence and red-brown color signaling reduced autofluorescence. The latter is seen in premalignant or early malignant lesions due to the increased thickness of the epithelium or tumor neovascularization24 (Fig 5 ). The targets of AFB are squamous cell neoplasms arising in the central airways. Numerous studies252627 have shown the superiority of AFB over white-light bronchoscopy in the detection of cancerous lesions; however, an impact on survival has not been elucidated, and, therefore, AFB is not yet recommended as a screening tool for lung cancer. Additionally, endobronchial carcinoma in situ seems overall to be an uncommon event (especially in countries with a rising prevalence of peripheral adenocarcinoma). Most identified abnormalities are of a metaplastic or dysplastic nature, and the value of intervention is unproven in these circumstances.2829
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EBUS utilizes a miniature probe with radial scanning capabilities that, after being coupled with the airway wall by a water-filled balloon, can visualize the layers of the bronchial mucosa, and reliably differentiates neighboring tumor masses, lymph nodes, and vascular structures. Information on the surrounding mucosa aids in distinguishing adjacent tumor invasion from mere external compression, as well as determining the depth of an endobronchial neoplastic growth, which ultimately influences the utility of surgical resection or endobronchial treatment in an early-stage cancerous lesion.3031 Many interventional pulmonologists now consider an EBUS examination a necessary step in the evaluation of suspected carcinoma in situ lesions to assess the likelihood of endoscopic treatment success.
One of the greatest benefits of EBUS is the real-time guidance of transbronchial needle aspiration of mediastinal lymph nodes. A new dedicated EBUS bronchoscope is now available and is equipped with a built-in US probe that is capable of curvilinear scanning, which produces a sectorial image of the surrounding lymph nodes and allows real-time sampling (Fig 6 ). A number of prospective studies323334 have documented the high sensitivity (85 to 95.7%), high specificity (100%), and high accuracy (89 to 97%) of EBUS-transbronchial needle aspiration in the diagnosis of enlarged mediastinal lymph nodes. A randomized clinical trial35 showed a higher yield for EBUS-guided lymph node sampling vs that for standard aspiration in all locations except the subcarinal region (84% vs 58%, respectively).
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In this arena, advanced diagnostic endoscopy may reshape the current algorithm in lung cancer staging; it is reasonable to predict that combined endobronchial and esophageal US endoscopy may replace mediastinoscopy as a primary staging procedure in many patients. Trials that will further outline the role of endoscopy are currently being planned.
Pleural Interventions
Pleural diseases represent a common problem encountered by pulmonologists in their daily practice. However, surveys37 have shown that fewer than two thirds of pulmonary physicians perform pleural procedures as simple as chest tube insertion. This has led to a practice pattern in which pleural procedures are directed toward interventional radiologists and thoracic surgeons.
As pulmonology is uniquely suited to take care of patients with pleural disorders, IP took an interest in pleural disease and sought to empower physicians in the field to handle pleural pathologies in a comprehensive manner, starting from an evaluation with US-guided thoracentesis or tube thoracostomy and ending with definitive management using pleurodesis via medical pleuroscopy. Mastering thoracic US is an important skill for interventional pulmonologists. US is used as a complimentary tool to further assess pleural abnormalities (eg, volume and loculation of pleural effusions, pleural masses, and pleural thickening), to mark the best insertion sites for needles and catheters, and to confirm tube placement or assess complications following pleural procedures. Although data are conflicting and randomized controlled trials are lacking, several studies3839 have shown a decreased rate of complications when thoracentesis is guided by US.
Besides the placement of large-bore chest tubes, the interventional pulmonologist possesses skills in the placement of small-bore pleural catheters (dubbed as pigtail catheters) and long-term indwelling pleural catheters. The former is a less-invasive method of draining the pleural cavity with a smaller tube (8F to 14F), resulting in minimal pain, an invisible scar, and effective fluid drainage. Talc pleurodesis has been accomplished using these tubes with a success rate comparable to those of larger chest tubes; however, their use in patients with empyema or hemothorax may not result in optimal drainage due to tube clogging.40
Tunneled pleural catheters are used on an outpatient basis for the intermittent drainage of malignant pleural fluid. They are as effective as chemical pleurodesis in relieving patients’ dyspnea and can lead to spontaneous, albeit often delayed, pleurodesis in up to 46% of patients.41
Medical pleuroscopy is an evaluation of the pleural space that is performed by the interventional pulmonologist as an alternative to closed pleural biopsy and video-assisted thoracic surgery.42 The procedure is performed with a conventional rigid or a semi-rigid pleuroscope (similar in design to a bronchoscope). The evaluation proceeds with the insertion of the pleuroscope into the pleural space through one or two incisions with the patient under moderate sedation. This tool enables the operator to inspect the pleural layers, drain pleural fluid, perform targeted biopsies of the parietal pleura, and insufflate talc for chemical pleurodesis (Fig 7 ). Medical pleuroscopy has proven to be safe and effective, and far superior to closed pleural biopsy in establishing a diagnosis of a pleural pathology.43 Video-assisted thoracic surgery, performed by thoracic surgeons in the operating room under general anesthesia with double-lumen intubation and collapse of the targeted lung, remains the "gold standard" for the evaluation and management of a complex pleural space and for the sampling of lung tissue.
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The indications for PT are identical to those for ST and consist of the establishment of airway access for long-term mechanical ventilation, the need for a conduit for pulmonary toilet, and the relief of upper airway obstruction. PT employs the modified Seldinger technique by introducing sequential dilators through the skin into the trachea to create a tract for the tracheostomy tube. Many operators use bronchoscopy for real-time guidance to ensure the correct placement of the wire and dilators.
The rate of complications with PT is low and is comparable to that with ST, as shown by multiple randomized controlled trials.45 Postoperative complications, particularly bleeding and infection, have been shown to be lower with PT, likely due to the reduced tissue trauma and the snug fit of the tracheostomy tube in the cutaneous-tracheal tract. Other advantages of PT over ST are cost reduction (related to the avoidance of operating room costs) and the elimination of the higher risk that may be involved in the transport of critically ill patients to the operating room.46
The interventional pulmonologist is ideally suited to perform PT due to their ability to handle late postoperative complications such as tracheal stenosis, tracheomalacia, and tracheoesophageal fistula. Surgical resection is the main treatment for a limited tracheal lesion, but for patients with complex long lesions or poor medical conditions, bronchoscopic interventions, such as balloon dilatation, laser incisions, or placement of silicone or Montgomery T-tube stents, can provide patients with symptomatic relief and a superior quality of life.4748 Other artificial airway procedures offered by IP include the placement of transtracheal oxygen catheter in patients with chronic pulmonary diseases requiring high concentrations of oxygen and the insertion of a minitracheostomy in patients with neuromuscular diseases who are in need of easy access to the airways to facilitate the suctioning of respiratory secretions.49
New Developments and Concepts in Evaluation
New innovations are continually fueling the growth of IP; while some are adopted from other fields and are tailored to pulmonary applications, others represent new pioneering concepts.
Therapeutic Developments
The microdebrider, a surgical tool routinely used by otolaryngologists and orthopedic surgeons, may also have a therapeutic role in the central airways. It is a powered instrument with a rotating blade inside a hollow metal tube that is connected to suction. When it comes in contact with tissue, it is capable of cutting and disposing of it in an efficient manner. In a study of 23 patients with benign and malignant tracheal conditions, the microdebrider was able to rapidly clear all obstructing lesions and keep a blood-free field with no procedure-related complications.50
Radiofrequency ablation is a thermal therapy that is traditionally applied percutaneously to treat primary or secondary malignancies of the lung. An interest in using this modality bronchoscopically has surfaced in the following three areas: its potential for use as an adjunct therapy in the removal of metallic stents by means of thermal destruction of granulation tissue51; its role in ablative treatment for pulmonary nodules and masses; and its possible therapeutic role in asthma.
The latter application has caught the attention of many physicians, given the broad health implications in a common disease like asthma in which a fraction of patients exhibit poor control with medical management alone. The hypothesis centers around the significant contribution of airway smooth muscles to the airway narrowing that is seen during asthma exacerbations and the prospect of decreasing airway hyperresponsiveness by reducing the smooth muscle mass with controlled low-energy radiofrequency ablation in the airways (Alair Bronchial Thermoplasty; Asthmatx; Mountain View, CA). Two preliminary studies5253 have demonstrated the safety and effectiveness of this treatment in patients with mild-to-moderate asthma with significant reduction in airway responsiveness to methacholine challenge, and improvement in peak flows and number of symptom-free days. A randomized controlled trial is currently underway.
Another promising application of therapeutic bronchoscopy in a common disease is bronchoscopic lung volume reduction in patients with emphysema. The National Emphysema Treatment Trial54 has shed some light on the benefits of surgical lung volume reduction while exposing the high mortality in patients with severely reduced pulmonary function. By the placement of one-way valves in the upper lobe bronchi of patients with upper lobe-predominant emphysema, upper lobe collapse can potentially be achieved, replicating the benefits of surgical lung volume reduction in a less invasive manner5556 (Fig 8 ). A large randomized study using one-way valves (the Endobronchial Valve for Emphysema Palliation Trial) has been completed, and efficacy as well as safety results should be available within 1 to 2 years. Multiple other approaches to endoscopic lung volume reduction for heterogeneous emphysema are under investigation. For patients with homogeneous emphysema, endoscopic extraanatomic airway bypass procedures are being evaluated.
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Narrow band imaging is a new bronchoscopic system equipped with filters that illuminates the target tissue at narrower red/green/blue bands of the light spectrum with delineation of the details of the microvascular network59 (Fig 11 ). Characterization of the vascular pattern of the bronchial epithelial surface promises to advance the understanding of angiogenesis in the early phases of carcinogenesis of lung tissue and the diagnosis of premalignant lesions.
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Training and Certification
IP is constantly growing and integrating new technologies. Acquiring the various skills and maintaining competence is a challenging undertaking. Current venues for training consist of dedicated 1-year IP fellowships, extended sabbaticals in IP centers, and 1- to 3-day condensed courses in selected procedures that are offered throughout the world.
There is an intense debate over whether a dedicated additional year of training is required or advanced skills can be obtained during the traditional 3-year fellowship training in pulmonary and critical care medicine. The argument is strongest for dedicated fellowship training. To master a procedural skill, the operator should not only perform a sufficient number of procedures but also should evaluate a large number of patients with a variety of medical conditions and learn, in the process, how to judiciously select optimal candidates for a specific procedure, when to seek alternative therapies, and how to deal with complications. Of equal importance, an operator should have access to all available tools and technologies so the best treatment can be offered to the patient, not just whatever is on hand locally. Therefore, it is clear that optimal training can only be acquired through dedicated extended learning periods in centers of excellence that provide state-of-the-art care to a high volume of patients.
Challenges and Future Directions
IP has quickly gained recognition and drawn interest from young trainees, industry, and hospital administrators. The allure is in the "instant gratification" associated with immediate procedural success, the introduction and use of new technologies and treatments, and the sense of empowerment felt with the ability to perform a series of therapeutic interventions by a single physician to the benefit of the patient. However, the reality does not mirror the perceived image, and there are numerous problems facing IP.
First, as a young field, IP is confronted by skepticism and may experience territorial battles with other disciplines. This may create a less than collaborative environment during the preliminary phase of establishing an IP practice.
Second, an exclusive practice of IP is currently not financially viable outside the realm of high-volume multidisciplinary airway centers in academic centers due to the low professional reimbursement. The current payment schema does not take into consideration the effort and risk put into such complex procedures as RB and the removal of large airway tumors. While the professional reimbursement for coronary artery stent placement is > $900, the payment for an airway stent insertion is in the range of $230 to $280 (https://catalog.ama-assn.org/Catalog/cpt/cpt_search.jsp).
Third, the present lack of regulation in the validation of training and the verification of competency is problematic. Although individual pulmonologists may be able to do any combination of IP procedures, ideally, the designation of "interventional pulmonologist" is reserved for a pulmonologist who has obtained formal training and has gained experience that spans the entire spectrum of IP skills.
To move forward, the IP community has to address these concerns in a cohesive and open-minded manner. The territorial battles are easily remedied by highlighting the multidisciplinary nature of IP and its positive impact on other specialties.
The financial concerns need to be addressed through representatives from professional pulmonary societies. The accreditation of IP training programs by the Accreditation Council for Graduate Medical Education and the establishment of an IP board examination or added certification are key steps to ensure the proper acquisition of IP skills and the protection of patients.
But, most importantly, IP has the responsibility of practicing evidence-based medicine. It is incumbent on interventional pulmonologists to conduct clinical trials to prove the benefits of their interventions and to study their limitations. Research efforts should address not only improvements in quality of life but also the detection of early disease and the prolongation of survival.
Summary
IP focuses on the diagnosis and treatment of malignant and nonmalignant airway and pleural disorders. A variety of new scopes, debulking modalities, and technological innovations have energized the field, and have extended its reach beyond the traditional limits of pulmonary medicine. The future growth of IP will depend on overcoming key issues impeding its progress through the regulation of training and credentialing, petitioning for fair financial reimbursement, and the conduct of rigorous scientific research.
Footnotes
Abbreviations: AFB = autofluorescence bronchoscopy; CAO = central airway obstruction; EBUS = endobronchial ultrasound; IP = interventional pulmonology; OCT = optical coherence tomography; PT = percutaneous dilatational tracheostomy; RB = rigid bronchoscopy; ST = surgical tracheostomy; US = ultrasound
Dr. Wahidi or his employer has received unrestricted grants for CME activities or research from Pentax, Denver Biomedical, and Olympus. He serves as a principal investigator on studies for endoscopic lung volume reduction and asthma treatment. Dr. Ernst or his employer has received unrestricted education grants for CME or research activities from Alveolus, Boston Scientific, Bryan, Cook, Denver Biomedical, Olympus, Storz, and Superdimension. He has served or serves as a principal investigator for studies on autofluorescense, endobronchial ultrasound, endoscopic lung volume reduction, and asthma treatment. Dr. Herth or his employer has received unrestricted education grants for CME or research activities from Alveolus, Boston Scientific, Bryan, Cook, Olympus, Storz, Wolf, and Superdimension. He has served or serves as a principal investigator for studies on autofluorescence, endobronchial ultrasound, and endoscopic lung volume reduction.
Received for publication April 11, 2006. Accepted for publication September 23, 2006.
References
This article has been cited by other articles:
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  A. J. Reddy, J. A. Govert, T. A. Sporn, and M. M. Wahidi Broncholith Removal Using Cryotherapy During Flexible Bronchoscopy: A Case Report Chest, November 1, 2007; 132(5): 1661 - 1663. [Abstract] [Full Text] [PDF]
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