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New applications for interventional bronchoscopy
Until recently, interventional bronchoscopy was limited to foreign body removal, debulking endobronchial tumours, or insertion of stents for the palliation of lung cancer. Most of these procedures are performed with a rigid bronchoscope under general anaesthesia by thoracic surgeons. As a result, only a few respiratory physicians developed an interest in interventional bronchoscopy. The small range of interventions has meant that, up to now, interventional bronchoscopy has been less glamorous than, for example, interventional cardiology.
Will this situation change? Firstly, there is an increased interest in transbronchial fine needle aspiration (TBNA) for staging lung cancer and in endobronchial ultrasound guided TBNA.1 The latter technique samples suspicious lymph nodes as small as 5 mm and has the potential for replacing mediastinoscopy. Secondly, tumours can be debulked with electrocautery, photodynamic therapy or lasers, and stents can be inserted under local anaesthesia with flexible bronchoscopes.
Recent research has driven an expansion of interventional bronchoscopy for some of the more common non-malignant respiratory diseases. Bronchial thermoplasty for the treatment of asthma is close to receiving FDA approval. This procedure, performed under local anaesthesia, involves the obliteration of smooth muscle in airways larger than 3 mm by applying radiofrequency energy. An endobronchial probe is passed through the working channel of the bronchoscope and applied to the airway wall. A controlled amount of energy is delivered which heats and destroys the muscle. Smooth muscle ablation causes a reduction in bronchial hyperreactivity and early studies suggest an improvement in asthma control. Pilot human trials have shown that the method is safe and can decrease airway hyperreactivity in patients with moderate asthma.2,3 Studies on patients with more severe or steroid dependent asthma are currently underway.
A number of procedures are being developed to improve breathlessness in severe emphysema. These aim to achieve volume reduction by bronchoscopy rather than surgery. The basic idea is to induce collapse of the worst affected lobe or segments by blocking the relevant airways with one-way valves. A number of such valves are available and have been designed to block inspiration while allowing drainage of expired air and secretions. This results in controlled deflation of the target segment or lobe. The valves are inserted directly through the working channel of the fibrescope or over a guide wire using the Seldinger technique. More than 100 patients have been treated in this way and the safety record to date is encouraging.4–6 The valves remain in place and have only seldom been implicated in cough or distal infection. Worthwhile improvements in lung function and quality of life have been reported in up to a third of patients and failure is probably due to collateral ventilation from surrounding lung units. This is not surprising since only patients with very severe emphysema have so far been treated and more work needs to be done to define the most suitable patients. A pivotal randomised trial is now underway.
While bronchoscopic valve placement has been proposed for patchy (heterogeneous) emphysema, an alternative intervention has been suggested for diffuse (homogeneous) emphysema. This involves the creation of extra-anatomical airways to bypass the flow limiting segment airways in expiration. A needle catheter is used to make fenestrations connecting emphysematous lung to nearby cartilaginous airways, and these holes are held open by “spiracles” (similar to small vascular stents). Pilot studies have shown that these fenestrations can be created safely and have a beneficial effect on lung function.7,8 There is, however, a tendency for the fenestrations to become blocked by granulation tissue.
Bronchoscopic instillation of delivery systems for slow release of drugs may open up new perspectives in the localised treatment of lung conditions. Some polymers have thermotropic properties and so behave as liquids at room temperature but form gels at body temperature. These can be injected into a part of the lung where they are cleared slowly and act as a drug efflux reservoir. These polymers also have a number of influences on cells ranging from effects on drug efflux channels to energy depletion in mitochondria. One such effect is to improve the sensitivity of drug resistant cells to chemotherapy. The natural development of this technology would be to directly instil specific drug eluting gels into the lung via a bronchoscope. For example, a polymer and chemotherapy drug combination could be injected into the target segment of the lung where it forms a gel and gradually elutes the chemotherapeutic drug and also improves the sensitivity of the cells to the treatment. The development of this technology is speculative at present but may have widespread applications in respiratory medicine—ranging from chemotherapy for lung cancer through to gene therapy for cystic fibrosis and regenerative treatments in emphysema.9
These interventions stimulate the future of interventional bronchoscopy. Some may fail to become a clinical reality, but this is likely to be a fertile area of research in years to come. It is clear that interventional bronchoscopy is evolving and will have an impact on a greater number of patients with respiratory diseases in the future.
The authors thank Dr Atul Mehta (Cleveland Clinic) for his review and comments.
New applications for interventional bronchoscopy