Nebulizers

A variety of nebulizers are used, usually in hospital settings. The two major types of nebulizers are the jet and ultrasonic devices shown in Figs. 4 and 5, respectively. Jet nebulizers operate on the principle that by passing air at high speed over the end of a capillary tube, liquid may be drawn up the tube from a reservoir in which it is immersed (Venturi or Bernoulli effect) [114]. When the liquid reaches the end of the capillary, it is drawn into the airstream and forms droplets that disperse to become an aerosol. An ultrasonic generator uses a piezoelectric transducer to induce waves in a reservoir of solution [115]. Interference of these waves at the reservoir surface leads to the production of droplets in the atmosphere above the reservoir. An airstream is passed through this atmosphere to transport the droplets as an aerosol. Both of these methods successfully produce droplets in the size range for inhalation [116-119]. The success of these devices can be measured by their use in the treatment and diagnosis of respiratory disease. Because of the size of the droplets,

Baffle

Baffle

Figure 4 Schematic of jet nebulizer. (With permission of Drug Topics.)

approximately 1-2 mm, the mass carried is small, and, therefore, the dose is administered over an extended period, which on average is 10-15min. The droplets produced are small enough to penetrate to the lung periphery. Early nebulizer therapy involved the generation of mists of water or saline for inhalation [120-124]. By radiolabeling the droplets with a gamma-emitting radioisotope and by having patients inhale the aerosol, the lungs can be imaged by gamma scintigraphy [125,126]. This method enables areas of poor ventilation, symptomatic of a disease state, to be identified. Standardized provocation tests for allergy studies also use this method of delivery [127,128]. Nebulizers are commonly used with solutions of bronchodilators, such as albuterol and terbutaline, for patients who cannot use metered-dose inhalers (MDIs) or who are suffering from severe asthma that requires hospitalization [129-132].

Transducer

Figure 5 Schematic of ultrasonic nebulizer. (With permission of Drug Topics.

Transducer

Figure 5 Schematic of ultrasonic nebulizer. (With permission of Drug Topics.

Additionally, sodium cromoglycate [90,133], corticosteroids [91], and pentamidine [134] have been administered by nebulizer. These devices are more effective generators of small particles than both MDIs and dry powder generators [8]. This results in a greater proportion of the dose reaching the lower airways, although each solution droplet contains less drug than each particle generated from an MDI or dry powder generator. As an example of the adult dose administered by nebulizer therapy, 1.25-5 mg albuterol sulfate is administered in 2-5 mL or more of 0.9% sodium chloride every 46 hr. Often, nebulizers are operated continuously, and the patient is asked to take intermittent breaths from each dose. Between breaths, the aerosol may be vented into the room. This approach leads to inconsistent and unpredictable dose administration to the patient. Some variation in total output, particle size, and overall efficiency exists among different generators [116,119,135-139].

Figure 6 shows a photograph of three jet nebulizers. Numerous jet nebulizers are being marketed, and, indeed, some concern has been expressed about the "nebulizer epidemic" [140,141]. The first two nebulizers shown were selected because they are both used to deliver pentamidine to patients suffering from Pneumocystis carinii pneumonia, a secondary infection in AIDS. Of note, ultrasonic nebulizers have also been used for this purpose. Treatment of this particular disease is the most notable example of nebulizer therapy in recent years. Significantly, no other method of pentamidine aerosol generation is currently available.

Modifying two hospital jet nebulizers, a Bird Micronebulizer and an Acorn II, to allow a solution feed, at 0.1-0.6mL/min, showed that the respirable (% <5 mm) output characteristics of these devices varied between 70-87% and

Coping with Asthma

Coping with Asthma

If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.

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