What is aerosol therapy?
Aerosol therapy is a technique of administering medication directly into the airway and lungs. An aerosol is a suspension of liquid and/or solid particles, usually administered by a medical device like an inhaler. A medical device is used to convert the medication into fine aerosol particles which can be inhaled or propelled directly into the airway and lungs. Bronchodilators and corticosteroids are the most commonly administered inhalation medications.
What are the uses of aerosol therapy?
The primary use of aerosol therapy is treatment of respiratory disorders that include:
- Obstructive lung diseases such as:
- Pulmonary arterial hypertension
- Infectious pulmonary diseases
With the advent of macromolecular (molecules of high mass) medications, aerosol therapy is being investigated for use in many non-respiratory systemic diseases. Inhalation therapy can be a convenient alternative to injections for chronic conditions, and improve patient comfort.
Macromolecular medications, because of their biochemical properties, are unsuitable for oral intake and require parenteral administration (injections into skin, muscle or veins). Advancement in aerosol delivery systems has enabled better efficiency and accuracy in delivering medications directly to the lungs, where they are rapidly absorbed into the bloodstream.
Aerosol therapy is currently being studied for use in several non-respiratory conditions that include:
What are the benefits of an aerosol treatment?
The benefits of aerosol treatment include the following:
- Direct delivery to the treatment site
- Faster onset of action than oral medication
- Lower requirement of dosage than systemic administration
- Reduced systemic adverse effects
What are the modes of aerosol drug delivery?
Following are the modes of aerosol drug delivery:
Metered dose inhalers
A metered dose inhaler (MDI) is a handheld device that uses a pressurized metal canister with a metering valve to deliver precise doses of medication. The canister is encased in a plastic sleeve with a mouthpiece to use for inhalation. The canister is pressed down (actuation) to release a measured dose of medication.
The canister contains a combination of the following:
- The medication as a solution or suspension.
- A surfactant, which is a substance that reduces surface tension and helps disperse the solution into aerosol particles.
- A propellant that propels the particles forward.
- Can deliver multiple doses
- Low risk of bacterial contamination
- Need for actuation and inhalation to be precisely coordinated
- Deposition of the medication in the mouth and throat
- Possible flammability of the pressurized propellant
- Cannot be used by people with sensitivity or cardiotoxicity to propellants
Inhalation accessory devices
Inhalation accessory devices enhance the action of metered dose inhalers. These devices are attached to the mouthpiece of the metered dose inhalers to expand and slow down the propelled high-pressure spray into a fine mist. There are two types of inhalation accessory devices:
- Spacers: Spacers are devices that provide space for the aerosol spray to slow down and become a fine mist. Children can use spacers with a pediatric mask. There are two types of spacers:
- Open tube spacers: An open tube spacer is an extension that provides extra space to slow down the spray.
- Reverse-flow spacers: Reverse-flow spacers direct the flow of drug away from the spacer’s mouthpiece and sound an alert if the patient inhales too quickly.
- Valved holding chambers: Valved holding chambers have a one-way valve which keeps the mist of medication inside the spacer until the patient inhales through the valve. Most devices sound an alert if the patient inhales too quickly.
- Enhanced drug delivery
- Removes the need for coordination of inhalation with actuation
- Prevents exhalation of air into the device
- Reduced drug deposition in the mouth and throat
- Bulkier in size and volume
- Possible bacterial contamination; must be regularly cleaned
- Static electricity may reduce drug delivery to the lungs
Dry powder inhalers
Dry powder inhalers (DPI) are devices that contain medication in the form of minute particles inside a capsule or blister. The blister/capsule is punctured before inhaling the medication through the mouthpiece. Dry powder inhalers do not use any propellant and are actuated by the patient’s breathing.
Following are some of the types of dry powder inhalers:
- Diskus: A disk shaped device with a coiled strip of blisters punctured with a rotating wheel.
- Aerolizer: A plastic device with a button to puncture capsules.
- HandiHaler: A spherical plastic device with a button to puncture capsules.
- Twisthaler: A device with a twisting mechanism to deliver measured doses of dry powder medication.
- Flexhaler: A device that uses a twisting motion to puncture capsules.
- No propellant
- No need of spacers
- Actuated by breath, so no need of coordination
- Require good inhalation flow rate, so are not appropriate for patients with acute asthma attacks or children with reduced lung function
- Drug deposition in the throat
- Humidity may cause the powder to clump and prevent dispersal
Nebulizers are electrical devices that transform drug solutions into breathable aerosol particles, in a process known as nebulization. Tabletop nebulizers can be plugged into wall sockets, while portable models run on batteries.
Nebulizers are useful for administering inhalation medication to patients who are too ill or too young to use other inhaling devices. Nebulizers can be used with a mouthpiece or a mask.
There are three types of nebulizers:
- Pneumatic jet nebulizer: Uses compressed gas to nebulize the solution. A powered compressor sends pressurized air or oxygen through a tubing into a cup of liquid medication aerosolizing it.
- Ultrasonic nebulizer: A compact single unit that uses high-frequency vibrations to nebulize the medication. The aerosol particles may be slightly larger than those produced by jet nebulizers. Ultrasonic nebulizers are not efficient in nebulizing suspensions.
- Mesh nebulizer: Mesh nebulizers are portable battery-operated devices that use a very fine mesh to break up the solution into aerosol particles. Mesh nebulizers are the latest products and produce the finest aerosol particles, but are also the most expensive.
- Useful for patients who cannot use other types of inhalation devices
- Large doses of medicine can be administered
- Patient coordination is not required
- Higher cost
- Harder to carry around
- Takes longer to set up and administer medication
- Jet nebulizers need a compressed gas source.
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