Aerosol drug therapy is a type of treatment that uses a special device to deliver medication directly to the lungs in the form of a fine mist. This type of therapy is also sometimes called inhalation therapy and can be used to treat a wide range of respiratory diseases.

In this article, we will discuss how aerosols are used to treat respiratory conditions, how the therapy works, and what the possible side effects are. We included helpful practice questions for your benefit as well.

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What is Aerosol Drug Therapy?

An aerosol is a suspension of fine particles dispersed in air or gas. They are generated by nebulizers and inhalers, which break up liquid or powder medications into particles small enough that can be inhaled into the lungs.

This is known as aerosol drug therapy, which can be used to treat a variety of respiratory conditions, including:

  • Asthma
  • Chronic obstructive pulmonary disease (COPD)
  • Bronchitis
  • Cystic fibrosis

The primary goal of aerosol drug therapy is to deliver a dose of a specific drug to the lungs in order to achieve a therapeutic effect. The effectiveness of aerosol therapy depends on several factors, including aerosol output, particle size, deposition, and delivery. 

Aerosol Drug Delivery Systems

A specialized device is required to generate aerosols in order for this type of therapy to occur. There are three primary types of aerosol delivery systems, including the following:

  1. Metered Dose Inhaler (MDI)
  2. Dry Powder Inhaler (DPI)
  3. Nebulizers

There are pros, cons, advantages, and disadvantages of each type. The technique for drug delivery is also different for each device.

Metered Dose Inhaler

A metered-dose inhaler (MDI) is a type of inhaler that uses a pressurized canister to deliver a specific amount of medication in aerosol form. The patient can activate the device while inhaling to receive a dose of the drug. 

One of the primary advantages of this type of inhaler is that they’re portable and easy to use. They’re also consistent in the amount of medication that is delivered with each inhalation.

Metered Dose Inhaler (MDI)
MDIs are the preferred aerosol delivery method for the maintenance delivery of bronchodilators and steroids in spontaneously breathing patients.

However, they are highly technique-dependent. This means that you must instruct the patient on how to properly use the device. Otherwise, they may not receive the full dose of the desired medication.

To reduce oropharyngeal deposition and the need for hand-breath coordination, spacers and valved-holding chambers can be used.

They’re accessory devices that attach to the inhaler and hold the medication in a chamber with one-way valves. This makes it easier for the patient to inhale the medication and reduces waste.

Dry Powder Inhaler

A dry powder inhaler (DPI) is a breath-actuated device that delivers aerosols in the form of fine powder particles that can reach the lungs by inhalation.

Dry powder inhalers are advantageous because they do not require a propellant for use. In addition, the patient does not need hand-breath coordination in order to receive a drug dose from this type of device.

Dry Powder Inhaler (DPI)

One of the primary disadvantages of dry powder inhalers is that their operation depends on turbulent flow and the patient’s inspiratory flow rate.

In other words, the patient must be able to perform a deep and fast inhalation in order to receive a drug dose from this device.


A nebulizer is a device that uses compressed air or ultrasonic waves to break up liquid into aerosol particles that can be inhaled into the lungs. It requires the use of a face mask or mouthpiece in order for drug delivery to occur.

Nebulizers are the preferred drug delivery method for patients who are unable to use an inhaler or for those who require high doses of medication.

Small Volume Nebulizer (SVN)

Types of nebulizers:

  1. Jet nebulizers
  2. Ultrasonic nebulizers
  3. Vibrating Mesh nebulizers

Each type has its own advantages and disadvantages. Jet nebulizers are the most common type. This includes small-volume nebulizers (SVN) and large-volume nebulizers (LVN), which are commonly used in the acute care setting.

Ultrasonic nebulizers (USN) use a piezoelectric crystal to generate aerosol particles by converting electrical signals into high-frequency vibrations. USNs have the ability to generate a higher aerosol output than jet nebulizers.

Vibrating mesh nebulizers (VMN) use a mesh with tiny holes that vibrate at a high frequency to produce aerosol particles. VMNs have the advantage of being able to generate a consistent particle size and have a higher respirable fraction than jet nebulizers.

Hazards of Aerosol Drug Therapy

Most of the hazards that occur when delivering aerosol drugs involve an adverse reaction to the medication that is being administered to the patient. However, some other hazards include:

  • Infection
  • Airway reactivity
  • Pulmonary effects of the drug
  • Systemic effects of the drug
  • Eye irritation
  • Secondhand exposure

Infection can be avoided by using sterile equipment and techniques when administering aerosol drugs. Airway reactivity can be avoided by monitoring the patient closely during therapy.

Adverse pulmonary and systemic effects of a drug can be minimized by using the proper dose and delivery method.

Eye irritation can be avoided by using eye shields or by avoiding direct contact with the eyes. Secondhand exposure can be minimized by using ventilation systems and by avoiding close contact with others while administering aerosol drugs.

Aerosol Drug Therapy Practice Questions:

1. What does the aerosol particle size depend on?
It depends on the substance being nebulized, the method used to generate the aerosol, and the environmental conditions surrounding the particle.

2. How are medical aerosols generated in the clinical setting?
They are generated with devices that physically disperse matter into small particles and suspend them in gas.

3. How does a large volume ultrasonic nebulizer work?
It incorporates air blowers to carry mist to the patient for the delivery of bland aerosol therapy or sputum induction.

4. How do ultrasonic nebulizers work?
They use a piezoelectric crystal to convert electrical energy into high-frequency vibrations to produce aerosols. The aerosol output is directly affected by the amplitude setting.

5. How do you prime an MDI?
To prime an MDI, you should shake the device and release one or more sprays into the room air if the device is new or hasn’t been used in a while.

6. How is aerosol output measured?
By collecting aerosol that leaves a nebulizer and on a special filter

7. How are DPIs categorized?
They are categorized by the design of their dose containers.

8. How often do you assess a patient on continuous nebulization?
Assess them every 30 minutes for the first 2 hours, then hourly after that for adverse drug responses

9. What affects MDI performance and drug delivery?
Low temperatures can decrease the output of a CFC MDI, and if debris build up on the nozzle or actuator orifice, it reduces the emitted dose.

10. What are three examples of aerosol devices?
Atomizers, nebulizers, and inhalers

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11. What factor is most crucial in developing an effective program of aerosol drug self-administration in an adult patient requiring maintenance bronchodilator therapy?
Good patient education

12. What are the beneficial characteristics of using an MDI?
They are portable, compact, and easy to use.

13. What are heterodispersed aerosols?
Aerosols with particles of different sizes

14. What are the key mechanisms of aerosol deposition?
Inertial impaction, gravimetric sedimentation, and Brownian diffusion

15. What are the medication delivery issues for infants and children?
They have smaller airway diameters, faster breathing rates, lower minute volumes, and their nose breathing filters out large particles.

16. What are monodispersed aerosols?
Aerosols with particles of the same sizes

17. What are small volume ultrasonic nebulizers used for?
They are used for the delivery of aerosolized medications (i.e., bronchodilators, antibiotics, and anti-inflammatory agents).

18. What are the hazards of aerosol drug therapy?
Infection, airway reactivity, pulmonary and systemic effects of bland aerosols, drug concentration changes during nebulization, and eye irritation

19. What is therapeutic aerosol deposition influenced by?
Inspiratory flow rate, flow pattern, respiratory rate, inhaled volume, I:E ratio, and breath-holding

20. What are two methods used to measure medical aerosol particle distribution?
(1) Cascade impaction and (2) Laser diffraction

21. What contributes to the aging of aerosols?
The composition of the aerosol, initial size of the particles, time in suspension, and ambient condition

22. What does gravimetric analysis measure?
Aerosol weight

23. What happens to the temperature of a solution placed in an ultrasonic nebulizer?
The temperature of the solution increases.

24. What is a dry powder inhaler (DPI)?
It is a breath-actuated dosing system by which a patient creates an aerosol by drawing air through a dose of finely milled drug powder. The dispersion of powder into respirable particles depends on the creation of turbulent flow in the inhaler.

25. What is an aerosol emitted dose?
The mass (amount) of the drug leaving the mouthpiece as an aerosol

26. What is aerosol output?
The mass (amount) of fluid or drug contained in an aerosol

27. What is aerosol output rate?
The mass (amount) of aerosol generated per unit of time

28. What is aerosol aging?
The process by which aerosol suspension changes over time

29. What is a metered-dose inhaler (MDI)?
A pressurized canister containing a prescribed drug in a volatile propellant combined with surfactant and a dispersing agent

30. What is an aerosol?
A suspension of solid or liquid particles in air or gas

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31. What is a positive response indicated from continuous nebulization?
An increase in peak flow greater than 10% with a goal of at least 50%

32. What is a disadvantage of an MDI?
80% of the aerosol hits the back of the throat, depositing the medication in the oropharynx

33. What is an ultrasonic nebulizer capable of?
They produce higher aerosols outputs and densities than conventional jet nebulizers.

34. What is Brownian diffusion?
The primary deposition mechanism for very small particles that can travel deep within the lungs

35. What is gravimetric sedimentation?
When aerosol particles settle out of suspension and are deposited due to the pull of gravity

36. What is inertial impaction?
When aerosols in motion collide with and are deposited onto a surface

37. What is the blow-by technique?
A delivery technique where the aerosol is directed from the nebulizer to the patient’s nose and mouth from a distance of several inches from the face

38. What is the fundamental principle of aerosol deposition?
Only a fraction of the emitted aerosol will be inhaled, and only a fraction of what is inhaled will make it to the lungs

39. What is the most commonly prescribed method of aerosol therapy?

40. What is the primary hazard of aerosol drug therapy?
An adverse reaction to the medication

41. What is the relationship between GSD and the range of particle sizes?
The greater the GSD, the wider the range of particle sizes and; therefore, a more dispersed aerosol

42. What is the difference between a spacer and a holding chamber?
A spacer is valve-less and just adds distance from the point of discharge to the mouth. A holding chamber has valves for holding the medication.

43. Where should the aerosol generator be placed with IPPV?
It should be placed in the circuit close to the patient’s airway.

44. Why would you prime an MDI?
To mix the drug and propellant and to ensure that an adequate dose is provided.

45. Why would you use continuous nebulization?
For the treatment of refractory bronchospasm

46. What are the two most common laboratory methods used to measure medical aerosol particle size distribution?
Cascade impaction and laser diffraction

47. What are the three categories of DPIs?
(1) Unit-dose, (2) Multiple unit-dose, and (3) Multiple-dose drug reservoir

48. What is aerosol output?
The mass of aerosol generated per unit of time

49. What are the different types of aerosols?
Pollen, spores, dust, smoke, fog, and mist

50. Aerosol particles can change size as a result of what?
Evaporation or hygroscopic water absorption

51. What is aerosol aging?
The process by which an aerosol suspension changes over time

52. What is the aim of medical aerosol therapy?
To deliver a therapeutic dose of the selected agent to the desired site of action

53. What is the SPAG?
The SPAG was manufactured specifically for the administration of ribavirin (Virazole) to infants with a respiratory syncytial virus (RSV) infection. It incorporates a drying chamber with its own flow control to produce stable aerosols.

54. What is the baffle?
A surface on which large particles impact and fall out of suspension, whereas smaller particles remain in suspension, reducing the size of particles remaining in the aerosol

55. Before the initial use and after storage, what should happen to every MDI device?
Each MDI should be primed by shaking and actuating the device to the atmosphere one to four times. Without the priming, the initial dose actuated from a new pMDI canister contains less active substances.

56. What is a breath-actuated nebulizer?
An aerosol device that is responsive to the patient’s inspiratory effort and reduces or eliminates aerosol generation during exhalation; they can generate aerosol only during inspiration, which eliminates the waste of aerosol during exhalation and increases the delivered dose

57. What is a breath-actuated pressurized metered-dose inhaler?
A variation of a pMDI that incorporates a trigger that is activated during inhalation, which reduces the need for the patient or caregiver to coordinate the actuation with inhalation

58. What is a breath-enhanced nebulizer?
A nebulizer that entrains room air in direct relationship to the inspiratory flow of the patient; they generate aerosols continuously using a system of vents and one-way valves to minimize aerosol waste

59. Breath holding after inhalation of an aerosol does what?
It increases the residence time for the particles in the lungs and enhances distribution and sedimentation.

60. When assessing a patient’s response to bronchodilator therapy, you notice a decrease in wheezing accompanied by an overall decrease in breath sounds. What’s most likely the cause of this?
Increasing airway obstruction

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61. What are cascade impactors?
They are designed to collect aerosols of different size ranges on a series of stages or plates.

62. The CDC recommends that nebulizers should be what?
They should be cleaned, disinfected, rinsed with sterile water, and air-dried between uses.

63. What are chlorofluorocarbons (CFCs)?
They are gaseous chemical compounds that were originally used to power metered-dose inhalers but have been phased out of use.

64. How often should you clean holding chambers and spacers?
They should be cleaned monthly or as recommended by the manufacturer.

65. Which part of the lung is preferred for deposition of beta-adrenergic bronchodilators?
The lower airways

66. Cold air and high-density aerosols can cause what?
Reactive bronchospasm and increased airway resistance

67. What are the concerns of patients using disposable nebulizers at home?
There may be degradation of the performance over multiple uses.

68. What is continuous drug delivery?
When nebulization occurs over an extended period of time

69. How does an atomizer differ from an SVN?
Atomizers do not have baffles

70. What is the inspiratory flow requirement when using a DPI?
60 L/minute

71. DPIs should not be used for what?
They should not be used for the management of acute bronchospasm.

72. When should an MDI be activated for a ventilator patient?
You should coordinate the actuation of the MDI with the beginning of the ventilator inspiration.

73. Drugs for nebulization that escape from the nebulizer into the atmosphere, or are exhaled by the patient, can be inhaled by who?
They can be inhaled by the caregiver or anyone in the vicinity of the treatment.

74. When used in conjunction with high-frequency oscillatory ventilation, the administration of albuterol sulfate by a vibrating mesh nebulizer placed between the ventilator circuit and the patient airway has been reported to do what?
It has been reported to deliver greater than 10% of the dose to both infants and adults.

75. When using a 50-psi flowmeter to drive an SVN, you would normally set the flow at what?
6-8 L/min

76. Exhalation into the device before inspiration can result in what?
It can result in a loss of drug delivery to the lungs.

77. Eye irritation is caused by what?
It is caused by aerosol therapy that is administered via a face mask, which leaks from the mask during delivery.

78. Poor patient response to bronchodilator therapy often occurs because of what?
An inadequate amount of the drug reaches the airway

79. What is a potential problem with continuous bronchodilator therapy?
An increased drug concentration can be adversely given

80. What is priming?
A technique that involves shaking the device and releasing one or more sprays into the air when a pMDI is new or has not been used in a while

81. What is a propellant?
The component of an MDI that propels or provides thrust

82. A reservoir on the expiratory limb of the nebulizer does what?
It conserves drug aerosols

83. What residual drug volume?
It is the dead volume of medication that remains in the SVN after the device stops generating aerosol and “runs dry.”

84. What is the respirable mass?
The proportion of an aerosolized drug to reach the lower respiratory tract

85. What is the risk for caregivers and bystanders when administering aerosol drug therapy?
They are at risk of hazards from exposure to secondhand aerosol drugs.

86. What is sedimentation?
It occurs when aerosol particles settle out of suspension and are deposited due to gravity.

87. What is the most commonly used device for medical aerosol therapy?
Small-volume nebulizer (SVN)

88. Small-volume ultrasonic nebulizer can be used to administer what?
Bronchodilators, anti-inflammatory agents, and antibiotics

89. What is a spacer?
A simple valve-less extension device that adds distance between the MDI outlet and the patient’s mouth; this distance allows the aerosol plume to expand and the propellants to evaporate before the medication reaches the oropharynx

90. What are spacers and valved holding chambers designed to do?
They are designed to reduce both oropharyngeal deposition and the need for hand-breath coordination.

91. Is the mouthpiece better than the mask for delivering aerosol drugs?
As long as the patient is mouth breathing, there is little difference in clinical response between therapy given by mouthpiece and therapy given by mask.

92. What are the three categories of nebulizers?
(1) Pneumatic jet nebulizers, (2) Ultrasonic nebulizers, and (3) Vibrating mesh nebulizers

93. What is the recommended timing interval when using an inhaler?
Manufacturers recommended waiting 30-60 seconds between actuations.

94. In order to avoid an oral yeast infection, the patient should do what after inhaling a corticosteroid drug?
Rinse their mouth

95. What problems are associated with using a SPAG to deliver ribavirin?
(1) Caregiver exposure, and (2) Drug precipitation can jam the breathing valves or occlude the ventilator circuit

96. A typical SVN is powered by what?
It is powered by a high-pressure stream of gas that is directed through a restricted orifice.

97. What is a unit-dose DPI?
A type of DPI that dispenses individual doses of the drug from punctured gelatin capsules

98. Ultrasonic nebulizers use a piezoelectric crystal to do what?
To generate aerosol

99. What is volume mean diameter (VMD)?
The median diameter of an aerosol particle measured in units of volume

100. Baffling systems decrease what?
They decrease both the MMAD (size) and GSD (range of sizes) of the generated aerosol.

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101. When ribavirin and pentamidine are administered, where should the treatment be provided?
They must be administered in a private room that is equipped for negative pressure ventilation with adequate air exchange.

102. Without a dose counter, there is no viable method to determine what?
To determine how much drug is remaining in the MDI

103. What are some advantages of using an MDI?
They are inexpensive, light, compact, and resistant to moisture. They also provide a quick delivery and consistent doses. They are available with most anti-asthmatic drugs.

104. What are some disadvantages of using an MDI?
Some patients have difficulty with the coordination of activation and inspiration, and it can be time-consuming to teach. There is also the cold-freon effect, which is the inability to continue to breathe when the propellant is released into the mouth.

105. What patients cannot use a DPI?
Children under the age of 5 and patients unable to generate a sufficient inspiratory flow.

106. What are some of the advantages of using a spacer?
There is no need for hand-breath coordination, it increases drug deposition in the lungs, it reduces drug deposition in the mouth, it can be used in children with a face mask, and it decreases the incidence of oral thrush

107. What are the characteristics of a jet nebulizer?
It cools during operation, provides a small aerosol particle size, and is less expensive than the alternatives.

108. How effective is the “blow-by” technique in infants?
It is not very effective

109. How should drug dosages be adjusted when they’re being administered via SVN to patients receiving mechanical ventilation?
Administer 2 to 5 times the normal dose

110. What is the optimal flow rate when using an SVN?
6 to 8 L/min

111. What are the characteristics of ultrasound nebulizers?
They heat up during operation, produce larger aerosol particles, are more expensive, and create less noise that the alternatives.

112. What aerosol output is an ultrasonic nebulizer capable of delivering?
0.2 to 1.0 mL/min

113. What are the hazards of aerosol therapy?
Bronchospasm, over-hydration, overheating of inspired gases, delivery of contaminated aerosol, and tubing condensation draining into the airway

114. Why is particle size important in aerosol therapy?
The ability of aerosols to travel through the air, enter the airways, and deposit in the lung is largely based on particle size.

115. What devices generate therapeutic aerosols?
Atomizers and nebulizers

116. The mass of aerosol particles produced by a nebulizer in a given unit of time best describes which quality of an aerosol?

117. What is a common method to measure aerosol particle size?
Cascade impaction

118. What is used to identify the particle diameter, which corresponds to the most typical settling behavior of an aerosol?
Mean mass aerodynamic diameter (MMAD)

119. What is the primary mechanism for the deposition of large particles in the respiratory tract?
Inertial impaction

120. What will increase aerosol deposition by inertial impaction?
Variable or irregular passages and turbulent gas flow

121. Where do most aerosol particles in the 5-10 μm range deposit?
Upper airways

122. Where do most aerosol particles in the 1-5 μm range deposit?
Central airways

123. What term describes the primary mechanism for the deposition of small particles?
Brownian diffusion

124. Where do most aerosol particles that are less than 3 μm deposit?

125. How can you monitor a patient for the possibility of reactive bronchospasm during aerosol drug therapy?
Measure pre and post peak flow and the %forced expiratory volume in 1 second; auscultate for adventitious breath sounds; observe the patient’s response; and communicate with the patient during therapy

126. What is the preferred method of delivering a bronchodilator to spontaneously breathing patients who are intubated and receiving mechanical ventilation?
Metered-dose inhaler (MDI)

127. When fired inside the mouth, what percentage of the drug dose delivered by an MDI deposits in the oropharynx?
About 80%

128. Before inspiration and actuation of an MDI, the patient should exhale to which of the following?
Functional residual capacity

129. To ensure delivery of proper drug dosage with an MDI, which of the following must be done first?
The canister should be warmed to hand or body temperature, and the canister should be vigorously shaken.

130. What type of patients are most likely to have difficulty using an MDI inhaler?
Those who are in acute distress, infants and young children, and elderly patients

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131. What is a potential limitation of flow-triggered MDI devices?
The high flows necessary for actuation

132. Which type of patient would you recommend against using a flow-triggered MDI as the sole bronchodilator delivery system?
A patient that is likely to develop acute severe bronchospasm

133. The key difference between an MDI holding chamber and a spacer is that the holding chamber incorporates what?
A one-way inspiratory valve

134. What device would you select to deliver an aerosolized bronchodilator to a young child?
MDI with a holding chamber and mask

135. The proper use of a dry powder inhaler requires that the patient is able to do what?
Generate inspiratory flows of 60 L/min or higher

136. What device depends on the patient’s inspiratory effort to dispense a dose?
Dry powder inhaler (DPI)

137. For what patient groups is the DPI for bronchodilator administration NOT recommended?
Infants and children under 5 and patients with an acute episode of bronchospasm

138. Exhalation into which device can result in a loss of drug delivery?
Dry powder inhaler (DPI)

139. SVN output drops after lowering the patient’s bed while giving a treatment, but there is 3 mL of solution still left in the reservoir. How can you correct this problem?
Reposition the patient so that the SVN is more upright

140. What should you do to minimize a patient’s infection risk between drug treatments with an SVN?
Rinse the SVN with sterile water and air dry

141. The physician has ordered ribavirin (virazole) to be administered by aerosol to an infant with bronchiolitis. Which device would you use for delivery?
Small particle aerosol generator (SPAG)

142. What problems are associated with the delivery of virazole using a SPAG?
Caregiver exposure and drug precipitation in the ventilator circuit

143. For maintenance administration of bronchodilators to adult patients with adequate inspiratory flows, which aerosol devices would you recommend?
DPI and MDI with a holding chamber

144. What aerosol drug delivery systems would you not recommend for a toddler or small child?

145. What is the best way to confirm that a patient can properly self-manage a newly prescribed form of aerosol drug therapy?
Have the patient provide a return demonstration


What is Aerosol Output?

Aerosol output is a term that refers to the total mass or weight of the particles that are produced by an aerosol generator for dispersion. In general, the aerosol output will vary greatly depending on the drug delivery system that is used.

It is measured by collecting an aerosol particle on a filter once it is dispersed and analyzing the weight or quantity.

If you measure the weight, this is referred to as the gravimetric analysis, which is typically less reliable because of the weight changes that occur due to evaporation. Analyzing the quantity is a more reliable way of measuring aerosol output.

What is Aerosol Deposition?

Aerosol deposition is the process by which aerosol particles are removed from the air and settle onto surfaces. This can occur through several different mechanisms, including gravity, inertial impaction, and diffusion.

During aerosol therapy, a large portion of aerosol particles never make it to the lungs due to deposition in the back of the throat or in the larger airways.

This could be due to the aerosol particle size or the patient’s breathing pattern. As a practitioner, understanding how to control these variables is important for improving the overall delivery of aerosol therapy to your patients.

What is an Atomizer?

An atomizer is a device that is used to generate an aerosol. It typically consists of a cup or reservoir for the liquid medication, a power source, and a nozzle.

The most common type of atomizer is the piezoelectric crystal atomizer, which uses a piezoelectric crystal to generate vibrations that create an aerosol.

What is a Baffle on a Nebulizer?

A baffle is a device that is used to direct the airflow in a nebulizer. It is typically placed between the compressor and nozzle to help control the direction of the airflow.

They play a key role in the ability of a nebulizer to generate aerosol particles.

What is a Breath-Actuated Nebulizer?

A breath-actuated nebulizer is a type of nebulizer that produces aerosols during inspiration when negative pressure is generated by the patient. This is important because it prevents medication doses from being wasted.

When a patient takes a breath in, negative pressure is created, which activates the device so that medication is drawn into a reservoir and aerosols can be generated.

What is a Breath-Enhanced Nebulizer?

A breath-enhanced nebulizer is a type of nebulizer that generates continuous aerosols, which help increase the amount that is inhaled. They use a system of one-way valves and vents to limit the amount of medication that is wasted.

When a patient takes a breath in, there is an inspiratory vent that allows air to move into the nebulization chamber where aerosols are generated.

Then, as the patient exhales, the inspiratory vent closes so that the drug aerosols can only exist through a one-way valve that is located near the mouthpiece of the device.

What is Brownian Diffusion?

Brownian diffusion is the random motion of particles that are suspended in a fluid. This motion is caused by the collisions of the particles with the molecules of the fluid.

The spread of aerosol particles in air is due to Brownian diffusion. The size and shape of the particles will affect the rate of diffusion.

What is an Emitted Dose?

The emitted dose is the amount of drug that is emitted from an aerosol generator. It is typically expressed in milligrams or micrograms. Some aerosol delivery devices are able to generate higher doses than others.

What is a Propellant in an Inhaler?

A propellant is a gas that is used to expel medication from an inhaler device. The most common propellants are chlorofluorocarbons (CFCs), which have been phased out due to their negative impact on the environment.

Hydrofluoroalkanes (HFAs) are the most common type of propellant used in inhalers today. They are less harmful to the environment than CFCs but can still contribute to greenhouse gas emissions.

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Final Thoughts

Aerosol drug therapy has many variables that can affect the overall efficacy of the therapy. Respiratory therapists are responsible for understanding how these variables work in order to optimize the delivery of aerosol drugs to their patients.

We also have a similar guide on airway clearance therapy that I think you will find helpful. Thanks for reading and, as always, breathe easy, my friend.

Medical Disclaimer: This content is for educational and informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Please consult with a physician with any questions that you may have regarding a medical condition. Never disregard professional medical advice or delay seeking it because of something you read in this article. We strive for 100% accuracy, but errors may occur, and medications, protocols, and treatment methods may change over time.


The following are the sources that were used while doing research for this article:

  • Faarc, Kacmarek Robert PhD Rrt, et al. Egan’s Fundamentals of Respiratory Care. 12th ed., Mosby, 2020. [Link]
  • Faarc, Cairo J. PhD Rrt. Mosby’s Respiratory Care Equipment. 10th ed., Mosby, 2017. [Link]
  • Faarc, Gardenhire Douglas EdD Rrt-Nps. Rau’s Respiratory Care Pharmacology. 10th ed., Mosby, 2019. [Link]
  • “Aerosol Therapy for Obstructive Lung Diseases.” National Center for Biotechnology Information, U.S. National Library of Medicine, Nov. 2011,
  • “Fundamentals of Aerosol Therapy in Critical Care.” PubMed Central (PMC), 2016,

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