Methods of Aerosol Delivery 

Aerosols are produced in respiratory therapy by utilizing devices known as nebulizers. There are a variety of nebulizers in use today, but the most common is one in which the Bernoulli principle is used through a Venturi apparatus.

 

As discussed earlier, the Bernoulli principle states that when gas flows through a tube, it exerts a lateral wall pressure within that tube due to its velocity. As the gas reaches a smaller diameter in the tube, the velocity is increased, which decreases lateral wall pressure. This decrease in diameter within the tube is at a structure called a jet. Just distal to the jet is a capillary tube that is immersed in a body of fluid. The decreased pressure is transmitted to the capillary tube and fluid is drawn up it. When the fluid reaches the jet, it is then atomized.

 

The absolute humidity that will be delivered from these devices can be increased by the use of a heater. A baffle is distal to this atomization process in the stream of gas/fluid flow. Nebulization takes place here as the liquid is impelled against the baffle. This baffle causes the larger particles to coalesce and collect in the reservoir. The smaller particles will be delivered to the patient in aerosol form. If the baffle is not used, the device is known as an atomizer. When the baffle is used, it is then called a nebulizer. In addition to the physically placed baffle, any 90° angle to gas flow can be considered a baffle. Large bore corrugated tubing should be used with baffles. This will enable the aerosol particles to be delivered to the patient.

 

There are several ways to deliver aerosol therapy, and the modalities available today include:

1.                  Aerosol mask

2.                  Face tent

3.                  Mouthpiece

4.                  Aerosol tent (mist tent)

5.                  In conjunction with IPPB

 

Physician orders for aerosol therapy should contain identification of:

1.                  Type of aerosol

2.                  Source gas (FIO₂)

3.                  Fluid composition (NaCl, water, etc.)

4.                  Delivery modality 

5.                  Duration of therapy

6.                  Frequency of therapy

7.                  Temperature of the aerosol

 

When a prescribed aerosol therapy has been completed, be sure to chart your actions and observations, making sure to include the following information:

·        time of administration

·        duration of therapy

·        type or composition of the aerosol (NaCl)

·        pulse

·        respiratory rate and pattern

·        breath sounds

·        characteristics of sputum

·        if sputum was or was not produced

·        the ease of breathing

·        any benefits observed

·        and any other relevant observations.

 

The reasons for administering aerosol therapies include:

1.      For bronchial hygiene

a)      Hydrate dried secretions

b)      Promote cough

c)      Restore mucous blanket

2.      Humidify inspired gas

3.      Deliver prescribed medications

4.      Induce sputum lab culture 

 

Aerosol delivery is accomplished in a variety of ways:

·        metered-dose inhaler (MDI)

·        nasal spray pump

·        dry powder inhaler (DPI)

·        jet nebulizer

·        small volume nebulizer (SVN)

·        large volume nebulizer

·        small-particle aerosol generator (SPAG)

·        mainstream nebulizers

·        ultrasonic nebulizer (USN)

·        intermittent positive pressure breathing (IPPB) devices

 

Spray pumps are the most common devices used for nasal aerosol administration of: antiallergics, sympathomimetics, antimuscarinics, and anti-inflammatory drugs. The spray pump generates low internal pressure, and produces large particles that are well-targeted for nasal deposition.

 

Metered dose inhalers (MDIs) consist of a pressurized cartridge and a mouthpiece assembly. The cartridge, which contains from 150-300 doses of medication, delivers a pre-measured amount of the drug through the mouthpiece when the MDI is inverted and depressed.

 

One controversial problem with MDIs involves their use of chlorofluorocarbons (CFCs) which have been identified by scientists as culprits in causing the growing hole in the earth’s ozone layer, contributing to global warming and increased ultraviolet radiation. While the manufacture and importation of other sources of CFCs, like refrigerants, have been banned in the U.S. since 1996, the FDA exempted CFCs used in “medically essential” products like MDIs. Alternatives (such as hydrofluorocarbons—HFAs) to CFCs for use in MDIs have been discovered, and the FDA has already formulated plans for facilitating a transition from CFCs to alternatives like HFAs.

 

However, the FDA has stipulated that CFC-medications will not be phased out until:

·        acceptable treatment alternatives exist for a particular MDI or other drug product so that the patient can find a product that meets his or her medical,

·        the alternatives are marketed for at least one year and are acceptable by patients, and

·        the supply of alternative products is sufficient to ensure that there will be no shortages of the drug.

 

Successful delivery of medications with an MDI depends on the patient’s ability to coordinate the actuation of the MDI at the beginning of inspiration. Patients need to be alert, cooperative, and capable of taking a coordinated, deep breath. Patients should be instructed to:

1.      Be sure to shake the MDI canister well before using.

2.      Hold the MDI a few centimeters from the open mouth. 

3.      Holding the mouthpiece pointed downwards, actuate the MDI at the beginning of a slow, deep inspiration, with a 4-10 second breath hold. Late actuation, or at the end of the inspiration, or stopping inhaling when the cold blast of propellant hits the back of the throat will cause the medication to have only a negligible effect.

4.      Exhale through pursed-lips, breathing at a normal rate for a few moments before repeating the previous steps.

5.      Patients should also be instructed to rinse their mouths after taking the medication.

 

On June 9, 2004, the FDA put on display a Federal Register notice seeking public comment on a proposal for withdrawing “essential-use” status for albuterol metered-dose inhalers (MDIs) using chlorofluorocarbon (CFC) propellants. This notice is being issued because two alternatives, non-CFC-based, albuterol MDIs are now available. If the essential-use designation is removed, albuterol MDIs containing an ozone-depleting substance (ODS) could not be marketed after an appropriate transition period.

FDA has tentatively concluded that the two non-CFC based albuterol products will be satisfactory alternatives to the albuterol MDIs containing ODS. In today’s notice FDA is, among other things, soliciting comments on a number of issues including the effective date of the rule and the transition period.

CFCs have been commonly used as propellants for various pressurized products including MDI treatments for asthma and chronic obstructive pulmonary disease (COPD), which includes emphysema and chronic bronchitis. Since 1978, the use of CFC-emitting aerosol products in the United States has been generally banned because of increasing evidence that CFCs contribute to the depletion of the earth’s protective ozone layer.

 

As a result of an international agreement established through the Montreal Protocol on Substances that Deplete the Ozone Layer and the U.S. Clean Air Act, CFC production and importation have also been banned for all commercial purposes in the United States since January 1996. The only exceptions to these bans are products that are considered medically essential with no suitable alternatives. Albuterol CFC-containing MDIs for asthma and COPD have been considered exceptions from the ban. However, under the Montreal Protocol and the Clean Air Act we are expected to phase out these products when suitable alternatives are available.

 

Although there are compelling reasons to phase out the use of these products, as a public health agency FDA must also weigh the potential public health impacts of such an action.

 

Under FDA regulations, to remove an essential-use designation, FDA must find that:

• At least one non-CFC product with the same active drug is marketed with the same route of administration, for the same indication, and with approximately the same level of convenience of use as the CFC product containing that active ingredient; (for drug moieties with more than one available CFC product, such as albuterol, more than one non-ozone depleting alternative must be marketed).
• Supplies and production capacity for the non-CFC product(s) exist or will exist at levels sufficient to meet patient needs;
• Adequate U.S. post marketing use data are available for the non-CFC product(s); and
• Patients who are required to utilize the CFC product for medical reasons are adequately served by the alternative non-CFC product(s) and other available products.

The agency is providing a 60-day public comment period from date of publication on this matter. For additional information, go to: www.fda.gov.

 

In a “product news” item published in RT Magazine in August 2004, it was reported that, “FDA May Ban CFC-Based Albuterol MDIs
The US Food and Drug Administration (FDA) is considering lifting an environmental law exemption allowing the use of albuterol metered-dose inhalers (MDIs) using chlorofluorocarbon (CFC) propellants. Under the international Montreal Protocol on Substances That Deplete the Ozone Layer agreement and the US Clean Air Act, CFC production and importation have been banned for all commercial purposes in the United States since January 1996. CFC inhalers have been exempt because they are considered medically essential with no suitable alternatives.

 

Now, however, the FDA says that two non-CFC-based, albuterol MDIs are available. So, in June, the administration published a notice in the Federal Register seeking public comment on a proposal for withdrawing “essential-use” status for the inhalers. If the essential-use designation is removed, albuterol MDIs containing an ozone-depleting substance could not be marketed after “an appropriate transition period,” according to the FDA.

 

The American Association for Respiratory Care (AARC) supports this phaseout. Testifying before an FDA Pulmonary-Allergy Drugs Advisory Committee on behalf of the AARC in early June, Joseph Rau, PhD, RRT, FAARC, shared key concerns about the process that he says are shared by respiratory therapists nationwide. These include ensuring an uninterrupted supply of medications during the transition, keeping the transition as cost-neutral as possible for patients, and ensuring that patients fully understand how to use the replacement inhalers.

 

Rau said the AARC is calling for a complete ban on CFC MDI albuterol by December 31, 2005, the date when the last producer of pharmaceutical grade CFCs is scheduled to cease production. “