New Treatment for Refractory Asthma
New Treatment for Refractory Asthma
Asthma is a chronic inflammatory condition of the airways characterized by episodic symptoms of breathlessness, cough, and wheezing, which can wax and wane over time. Approximately 8.2% of the general population is affected.
Severe refractory asthma
The definition of asthma as severe and refractory is necessary to meet at least one of the following major criteria:
- Takes oral corticosteroids continuously or nearly continuously (> 50% of year)
- Takes high-dose inhaled corticosteroids.
In addition, the patient must meet at least two of the following minor criteria:
- Takes a controller medication such as a long-acting beta-agonist, theophylline, or a leukotriene antagonist every day;
- Takes a short-acting beta agonist every day or nearly every day;
- Has persistent airway obstruction, ie, a forced expiratory volume in 1 second (FEV1) less than 80% of predicted, or a peak expiratory flow that has a diurnal variability greater than 20%
- Has one or more urgent care visits for asthma per year
- Needs three or more oral corticosteroid “bursts” per year
- Has prompt deterioration when the dose of oral or inhaled corticosteroid is reduced by 25% or less
- Has had a near-fatal asthma event in the past.
Thermoplasty is a method that involves the delivery of radiofrequency energy to the airway wall which ablates the smooth muscle layer resulting in lessening the bronchoconstriction and improves asthma symptoms.
BRONCHIAL THERMOPLASTY PROTOCOLS
Patients are assessed before and on the day of the procedure to make sure their disease is stable (ie, their postbronchodilator FEV1 is within 15% of baseline values, and they have no evidence of asthma exacerbation or active infection), similar to the protocol used in the AIR2 trial, before proceeding with the treatment.
Patients are given 50 mg of prednisone 3 days before and again on the day of the procedure. Nebulized albuterol (2.5–5.0 mg) is given before the patients undergo screening spirometry and again before the procedure. If the preprocedure FEV1 is lower than 15% below baseline, we postpone the procedure to another day.
The procedure is performed with the patient under moderate conscious sedation, typically using fentanyl (Sublimaze), midazolam (Versed), and topical lidocaine in a monitored environment. The bronchoscope is inserted via either the mouth or nose, and supplemental oxygen is provided.
Thermoplasty is performed with the Alair system (Asthmatx, Inc., Sunnyvale, CA), which delivers a specific amount of radiofrequency (thermal) energy through a dedicated catheter. The catheter is deployed through a 2.0-mm channel of a flexible bronchoscope, starting in distal airways as small as 3 mm in diameter and working proximally to sequentially treat all airways to the mainstem lobar bronchi. The sites treated are meticulously recorded on a bronchial airway map to ensure that treatment sites are not skipped or overlapped (Video above)
An array of four electrodes is manually expanded to make contact with the airway walls; each electrode has 5 mm of exposed wire. As the energy is delivered, the control unit measures electrical resistance converted to thermal energy and turns off the current when an appropriate dosage is given. This thermal energy is what is responsible for altering the airway smooth muscle.
A full course of treatment requires three separate bronchoscopy sessions, each separated by 2 to 3 weeks. The left lower lobe and the right lower lobe are treated in separate procedures, and then both upper lobes are treated in a third procedure to minimize any respiratory symptoms. Each procedure usually requires 50 to 75 activations of the device and takes up to 60 minutes.
After each procedure the patient should be observed for 3 to 4 hours, and spirometry should be repeated to make sure the FEV1 (percent predicted) is within 20% of the baseline value. An additional 50-mg dose of prednisone is prescribed for the day after the procedure.
The FDA aproves the method in 2010.
One question that needs to be studied is whether thermoplasty will help other forms of bronchospastic lung disease, such as chronic obstructive pulmonary disease.