Nebulizers aerosols output from

There appear to be many contradictions in the literature concerning the efficacy of nebulizer therapy. It has been suggested that although an MDI delivers a much smaller dose than a nebulizer, the same effect is observed clinically. This may be explained in terms of the time taken to administer a dose using a nebulizer. The generally smaller-particle-size output from nebulizers in comparison with that of MDIs and the delivery as solution rather than as suspension explains the time required to deliver the dose by this method. The particle size advantage of nebulizers leads to their use when patients are admitted to hospitals with severe airways obstructions. Once their condition has stabilized, the patients are placed on MDI aerosol therapy, which is more convenient. 

Figure 17 Schematic describing experiments measuring aerosol output from Fisoneb ultrasonic nebulizer. (From Ref. 10.)...

During nebulization from airjet nebulizers, cooling of the reservoir solution occurs which, together with vapor loss, results in concentration of the dmg solution. This in turn produces an aerosol output in which the drag concentration increases with time. Concentration of the dmg solution in the reservoir can lead to drug recrystallization with subsequent blockage within the device or variation in aerosol particle size. 

Figure 21 Influence of ventilator choice on aerosol output expressed as inhaled mass (%) versus time for four ventilators utilizing the Misty-Neb nebulizer. (Baxter Healthcare Corp., Valencia CA from Ref. 32.)...

Figure 3 Circulaire nebulizer system. A traditional constant output jet nebulizer produces aerosol continuously by compressed air (compressor not shown). During patient inhalation, aerosol is drawn from the system by patient inspiration. During patient breath hold and exhalation (through one-way valve adjacent to mouthpiece) decompressed jet nebulized air containing aerosol fills an infiatable plastic bag for inhalation during subsequent breaths.

During development of the European standard, an interlaboratory trial was organized involving six laboratories within Europe to follow a defined protocol to assess aerosol output and size from two fundamentally different nebulizer systems. Results demonstrated that the methods were repeatable within +/- 10% of mean return for both aerosol output and aerosol size (unpublished data). Results of preliminary research investigating the correlation between in vivo response and in vitro estimate of aerosol output and size show a promising correlation (33), though further work is needed in this area. 

Many reviews on the relevant technical aspects for drug nebulization are available (e.g. [43 5]. The greatest disadvantages of nebulizers are their poor deposition efficiency (see Section 3.11) and low output rate (e.g. [46]). Several developments have been reported to improve their efficacy, like the use of open vents or breath-assisted open vents [47] and adapted aerosol delivery [48]. A renewed interest in nebulizer therapy may also come from the generation of special aerosols, such as hposomes [49]. 

The delivery efficiency, or the nebulizer output, can be expressed in many different ways, as widely documented in the literature. Sometimes it is represented as the volume output, or solution mass output. However, it is more practical to use the drug mass emitted from the nebulizer at or near the mouthpiece to estimate the nebulizer output, because the amount of aerosolized drug mass at this point in the system is the best measure of how much drug the patient has available to inhale. 

Figure 1 Sketch illustrating principles of the standing cloud technique. Aerosol particles produced hy the nebulizer are captured by the output filter, direct analysis of drug or a marker of the drug such as a radiolabel provides a quantitative estimate of nebulizer function. (Modified from Ref. 7.)...

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