These considerations have prompted others to investigate simpler techniques of aerosol delivery in acute asthma. Recently, it has been suggested that p- agonist delivered by metered dose inhaler with a spacer device is simpler and as effective as В N in this setting. However, some acutely ill patients are unable to use these devices properly while others are psychologically not prepared to accept a form of therapy that they perceive as already having failed at home. Continuous nebulization may achieve the goal of simplifying treatment while introducing a new mode of bronchodilator delivery in patients with acute airway obstruction.
There are several potential disadvantages of CN. Intermittent large doses of brochodilator may theoretically be superior to continuous low doses if tachyphy-laxis has occurred as a result of frequent prior use of medication. However tachyphylaxis to inhaled albuterol appears to be an issue of statistical but not clinical significance. Moreover, it was recently shown that long-term prior treatment with inhaled p-agonists decreases the duration, but not the peak response, to short-term administration of the same agents. Thus, increasing the frequency of aerosol administration or employing CN might be important in providing per-sistent bronchodilation in acutely ill asthmatic patients who previously have been receiving long-term p- agonist therapy by inhalation.
There are several technical limitations to the CN technique. One must be assured that the delivery system used has been carefully calibrated and is capable of supplying a constant dose of aerosol solution. We used a large volume jet nebulizer to administer continuous p-agonist therapy. This was selected as we did not want to repeatedly top off the volume in the nebulizer and wanted a model whose output would not change as the fluid within it gradually decreased. The disadvantages of this system included the wastage and hence expense of unused albuterol solution remaining in the reservoir when the treatment period was over. In addition, a large volume of fluid was nebulized, thus potentially reducing patient tolerance to this system. A modification of the systems described by Ba et al and Moler et al whereby the volume of fluid in a smaller nebulizer is maintained by means of a constant infusion pump may be preferable. Finally, CN of fluid and bronchodilator may cause facial irritation and promote maceration of skin underneath contact points of the mask. While this was not a problem for the brief time period of the present study, it remains to be seen whether this technique will be tolerated for prolonged intervals.
In summary, this feasibility study determined that continuously nebulized albuterol could be easily and effectively used as initial therapy in patients with acute exacerbations of asthma seen in the emergency department. The degree of bronchodilation achieved after 2 hours was similar to that obtained with standard intermittent (hourly) nebulizer therapy. Since CN of p-agonist has now been found to be safe and effective in the immediate treatment of airway obstruction, future studies should be done to determine whether there is any advantage to this technique with more prolonged therapy.