Humidity and Bland Aerosol Therapy Illustration

Humidity and Bland Aerosol Therapy: An Overview (2024)

by | Updated: Jun 12, 2024

Humidity and bland aerosol therapy are critical elements in respiratory care, particularly in managing conditions that impair the respiratory system.

Humidity, the presence of water vapor in the air, plays an essential role in maintaining the mucociliary function, thus facilitating natural lung clearance mechanisms.

Bland aerosol therapy, on the other hand, involves the delivery of sterile water or saline aerosols to the respiratory tract, often for the purpose of hydrating airway secretions and facilitating their removal.

Despite their evident utility, an in-depth understanding of their physiological impact and appropriate applications is essential for effective treatment outcomes.

This article provides an overview of humidity and bland aerosol therapy, their clinical applications, and helpful practice questions on these essential topics.

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What is Humidification Therapy?

Humidification therapy is a medical treatment commonly used in respiratory care to add moisture to the air that a patient inhales. It involves the addition of water vapor to gases that are delivered to the patient, usually via a respiratory device such as a ventilator, CPAP machine, or directly through a nasal cannula or face mask.

The primary goal of humidification therapy is to maintain the natural humidity level of the respiratory tract, thereby facilitating normal lung functions like gas exchange, mucociliary clearance, and the prevention of dryness that can lead to irritation or infection.

The human respiratory tract is naturally designed to condition inhaled air to a certain level of humidity before it reaches the delicate alveoli in the lungs.

When this natural humidifying function is compromised—due to illness, intubation, or breathing artificially dry air—various respiratory issues can arise.

For instance, dry airways are less effective at trapping and removing particulates, pathogens, and secretions. This can lead to an increased risk of infection, inflammation, and even lung damage over time.

Humidification therapy is frequently employed in a variety of settings, from intensive care units where patients may be intubated and unable to humidify air naturally to home care settings for individuals with conditions like obstructive sleep apnea.

Type of Humidification

Humidification therapy can be administered in various ways depending on the clinical context, the type of respiratory equipment being used, and the specific needs of the patient.

Here are some common types of humidification therapy:

  • Bubble Humidifiers: Primarily used with low-flow oxygen systems, air passes through a bottle of sterile water, creating bubbles and humidifying the oxygen.
  • Heat and Moisture Exchangers (HMEs): Also known as “artificial noses,” HMEs are placed between the patient and the ventilator. They capture heat and moisture from the patient’s exhaled air and use it to humidify the inhaled air.
  • Heated Humidifiers: These devices heat water to create water vapor, which is then added to the gas flow from the ventilator or other respiratory equipment. These are commonly used in ICU settings for intubated or tracheostomized patients.
  • Passover Humidifiers: In these systems, air passes over a cold water reservoir, picking up water vapor through the process. They are often used in home settings with CPAP or BiPAP machines for sleep apnea.
  • Nebulizers: Although more commonly associated with drug delivery, nebulizers can also be used for bland aerosol therapy by nebulizing sterile water or saline into fine particles that can be inhaled.
  • High-Flow Nasal Cannula (HFNC): This delivers warmed and humidified air at high flow rates (up to 60 L/min) through a nasal cannula. It is used in both pediatric and adult patients for various conditions, including respiratory failure and postoperative support.
  • Integrated Humidification: Some modern respiratory equipment comes with built-in humidification systems that automatically adjust based on sensor readings from the patient’s airway.

Each type of humidification therapy has its own set of benefits, limitations, and ideal use-cases.

For instance, HMEs are generally not suitable for patients with thick, copious secretions, while heated humidifiers offer more precise control over humidity levels but require more vigilant monitoring to prevent complications like hyperhydration or burns.

Therefore, choosing the appropriate type of humidification therapy requires a comprehensive understanding of the patient’s respiratory condition, the setting, and the available equipment.

Humidity and Bland Aerosol Therapy Vector Illustration

What is Bland Aerosol Therapy?

Bland aerosol therapy is a respiratory treatment that involves the delivery of sterile water or saline aerosols directly into a patient’s airway. Unlike medicated aerosols, which deliver drugs, bland aerosols only provide moisture. This therapy aims to humidify the respiratory tract and to loosen or dilute viscous secretions, facilitating their removal and aiding in the overall process of airway clearance.

It is commonly used in situations where natural humidification and mucociliary clearance mechanisms are compromised, such as in cases of atelectasis (lung collapse), bronchitis, or after surgery involving airway manipulation.

The aerosol particles in bland aerosol therapy are typically generated using a jet nebulizer, ultrasonic nebulizer, or other aerosol-generating devices. These particles are then inhaled through a mask, tracheostomy tube, or other interface.

The size of the aerosol particles and the composition of the solution can be adjusted based on specific clinical indications.

Bland aerosol therapy is often administered in conjunction with other respiratory treatments like bronchodilators or mucolytics.

However, it’s crucial for healthcare providers to use this therapy judiciously, as improper application can lead to complications such as hyperhydration, mucosal irritation, or increased risk of infection.

Types of Bland Aerosol Therapy

Bland aerosol therapy involves the delivery of sterile water or saline aerosols to the respiratory tract, usually with the aim of hydrating airway secretions and facilitating their removal.

Here are some common types of bland aerosol therapy based on delivery mechanisms and clinical indications:

  • Large Volume Nebulizer: Often used for sputum induction or hydration of thick mucus, this device can disperse large amounts of aerosol into a chamber where the patient inhales it via a mask or mouthpiece.
  • Small Volume Nebulizer: Typically handheld, these are generally used for short-term therapies, such as prior to a respiratory procedure or for acute relief.
  • Aerosol Masks: These are facial masks specifically designed to work with nebulizers to deliver aerosol therapy effectively.
  • Tracheostomy Collars: Designed for patients with a tracheostomy, these collars can be used with a nebulizer to deliver aerosols directly to the trachea.
  • Venturi Masks: Though generally used to deliver a mixture of oxygen and room air, some Venturi masks have ports for adding aerosols.
  • Face Tent: This is a loose-fitting facial mask that provides a chamber for aerosol accumulation, often used for patients who find masks claustrophobic.
  • Swivel Adapter Method: Sterile water or saline is instilled directly into the tracheostomy or endotracheal tube via a swivel adapter. This is followed by manual or mechanical ventilation to disperse the fluid as an aerosol.

Summary: Bland aerosol therapy is a specialized form of humidification therapy targeted at enhancing airway clearance and improving respiratory function. It is widely used in both acute and chronic care settings, but it requires careful administration and monitoring to maximize benefits and minimize potential risks.

Humidity and Bland Aerosol Therapy Practice Questions

1. What are the types of humidifiers?
Bubble humidifier, passover humidifier, heat and moisture exchanger (HME), and room humidifier

2. What does humidity therapy involve?
It involves adding water vapor and sometimes heat to an inspired gas.

3. Heat and moisture exchange is a primary function of what?
It is a primary function of the upper respiratory tract, mainly the nose.

4. Which is more effective at providing heat and moisture, the mouth or nose?
The nose is more effective.

5. What is ISB?
It stands for isothermic saturation boundary and is the point that is normally 5 cm below the carina.

6. What happens above the ISB?
The temperature and humidity decrease during inhalation and increase during exhalation

7. What happens below the ISB?
The temperature and relative humidity remain constant (BTPS).

8. What is BTPS?
It stands for: body, temperature at the pressure to which the patient is exposed and 100% saturated with water vapor.

9. What is the primary goal of humidification?
To maintain normal physiologic conditions in the lower airways

10. What are the indications for humidification therapy?
Humidifying dry medical gases, flows greater than 4 L/min, overcoming a humidity deficit created when the upper airway is bypassed, managing hypothermia, and treating bronchospasm caused by cold air

11. What are the clinical signs and symptoms of inadequate airway humidification?
Atelectasis, dry or nonproductive cough, increased airway resistance, increased incidence of infection, increased work of breathing, patient complaint of substernal pain and airway dryness, and thick dehydrated secretions

12. What is absolute humidity?
The actual amount of moisture contained in a gas

13. What is relative humidity?
The amount of water vapor a sample could maximally hold at a given temperature

14. What is body humidity?
The amount of water vapor in a gas sample compared to the capacity for water vapor at body temperature.

15. What is the expected body humidity value at normal body temperature?
44 mg/L

16. What best describes a humidity deficit?
The amount of water vapor needed to achieve full saturation at body temperature

17. What is bland aerosol therapy used for?
It is used to treat upper airway inflammation from croup, epiglottitis, and post-extubation edema.

18. How does a heater improve the effectiveness of a humidifier?
Heat improves the water output of humidifiers.

19. When should heat be delivered with a large-volume nebulizer?
It should be used if secretions are thick and hard to remove or if the patient’s upper airway is bypassed.

20. What are the four variables that affect the performance of a humidifier?
Temperature, surface area, time of contact, and thermal mass

21. What are the low-flow humidifiers?
Bubble and jet humidifiers

22. What is a hazard of using a bubble humidifier?
At a high flow rate, it can produce aerosols which can transmit pathogenic bacteria from the humidifier reservoir to the patient.

23. When should a bubble humidifier be used?
When a patient is on a nasal cannula or simple mask with a flow greater than 4 L/min or if the patient complains of a dry nose.

24. What problems could be wrong with a bubble humidifier if no sound is heard when pinching the tubing?
The inlet could be clogged, the reservoir could be cracked or loose, the gasket could be worn or missing, or the connection could be broken.

25. What is wrong if a bubble humidifier whistles by itself?
The oxygen flow may be too high, or the tubing may be kinked or obstructed.

26. What is wrong when no bubbling occurs in a bubble humidifier?
The capillary tube could be obstructed, there could be a loose connection, the oxygen flow may not be turned on, or there is inadequate pressure in the line.

27. What are the factors that influence the output of a bubble humidifier?
Temperature, relative humidity, and absolute humidity

28. What is the purpose of the pop-off valve on a bubble humidifier?
To warn of an obstruction and to prevent the bursting of the humidifier bottle

29. What is the expected water vapor output of a bubble humidifier?

30. What liter flows should be used with a bubble humidifier?
Flows of at least 2 L/min but not more 6 L/min

31. What type of probe does a servo-controlled heating system use at or near the patient’s airway?
Thermistor probe

32. What are the three most common problems with humidification systems?
(1) Dealing with condensation, (2) Avoiding cross-contamination, and (3) Ensuring proper conditioning of the inspired gas

33. What are some factors that would influence the amount of condensation in a humidified system?
(1) Temperature difference across the system, (2) Ambient temperature, (3) Gas flow, (4) Set airway temperature, and (5) The length, diameter, and thermal mass of the breathing circuit

34. What does particle size depend on?
It depends on the substance that is being nebulized, the methods used to generate the aerosol and the environmental conditions.

35. How does an HME work?
It acts as an artificial nose and captures exhaled heat and moisture and uses it to heat and humidify the next inspiration.

36. What type of humidifier uses a filter?
Heat-moisture exchangers (HME)

37. When should an HME be used?
When the patient’s upper airway is bypassed during mechanical ventilation.

38. What is the correct placement of an HME?
It should be placed 10 cm away from the endotracheal tube and proximal to the ventilator circuit.

39. What are the three types of HMEs?
Simple (high thermal conductivity) condenser humidifier, hygroscopic (low thermal conductivity) condenser humidifier, and hydrophobic (water repellent element) condenser humidifier.

40. What type of humidifier is known as an “artificial nose?”
Heat-moisture exchangers (HME)

41. What are the contraindications for using an HME?
Thick, copious, or bloody secretions; expired tidal volume less than 70% of the delivered tidal volume; body temperature less than 32 degrees C; high spontaneous minute volume greater than 10 L/min; and in patients who are receiving an in-line aerosol drug treatment

42. How can you tell if the HME is working properly?
If the patient is receiving proper heat and moisture

43. When should HME be changed to a large-volume nebulizer with a heater?
When secretions can’t be broken up

44. Why is it a problem that large reservoir systems must be manually refilled?
This is problematic because when the system is opened for refilling, cross-contamination can occur.

45. What is Bernoulli’s principle?
When gas in a tube exerts lateral wall pressure due to the gas velocity

46. What type of humidifier deals with Bernoulli’s principle?
Jet humidifiers

47. What is the purpose of a room humidifier?
To help with sinusitis and drainage.

48. How does a room humidifier work?
It creates an aerosol that exits the device and evaporates in the ambient air, increasing the humidity of the room.

49. What is a hazard of a room humidifier?
It has the potential to spread infections.

50. How does condensation occur?
Saturated gas cools as it leaves the point of humidification and passes through the delivery tubing to the patient. As the gas cools, its water vapor capacity decreases, causing condensation.

51. How is condensation disposed of?
It is treated as infectious waste and drained into an infectious waste container.

52. What is the formula for relative humidity?
%RH = content/capacity x 10

53. What is the capacity of water at body temperature?
44 mg/L

54. What is the formula for body humidity?
Absolute humidity / 44 mg/L x 100

55. What is a humidity deficit?
Inspired air that is not fully saturated at body temperature

56. What is the formula for humidity deficit?
44 mg/L – absolute humidity

57. What are the indications for humidification and warming of an inspired gas?
Dry gases that are at a flow greater than 4 L/min; following intubation; managing hypothermia; and treating bronchospasm caused by cold air.

58. What is a humidifier?
A device that adds molecular water to a gas, occurring by the evaporation of water from a surface

59. What are the factors that affect a humidifier’s function?
Temperature; the higher the temperature of a gas, the more water it can hold; surface area, time of contact, thermal mass; the greater the amount of water in the humidifier, the greater the thermal mass

60. What are the types of humidifiers?
Bubble, Passover, wick, HME, and cascade

61. How much deadspace does an HME add?
30-90 mL

62. What are the types of heating elements that require an electrical source?
Hot plate, wraparound, yolk or collar element, immersion type, and a heated wire-ventilator circuit

63. What amount of humidity is used for intubated patients?
At least 30 mg/L

64. What piece of equipment is used to measure humidity?

65. How much can an unheated large-volume nebulizer put out?
26-35 mg H2O/L

66. How much can a heated large-volume nebulizer put out?
35-55 mg H2O/L

67. What is an ultrasonic nebulizer?
An electrically powered device that uses a piezoelectric crystal to generate aerosol. The crystal transducer converts radio waves into high-frequency mechanical vibrations that produce aerosols.

68. What does the amplitude do to the ultrasonic nebulizer?
It directly affects the volume of aerosol output. You cannot change the frequency, but you can increase the amplitude.

69. What are the types of aerosol masks?
Aerosol mask, trach collar, t-piece, face tent, mist hoods, and tents for small children and infants

70. What is the most effective humidifier/heater on the body?
The nose

71. What puts stress on the lower airway in order to provide heat and moisture?
An artificial airway

72. What is indicated following the intubation of a patient?
Humidification and warming of inspired gases

73. What is a device that adds molecular water to gas?

74. The higher the temperature of the gas in the humidifier?
The more water it can hold

75. What type of humidifier breaks an underwater gas stream into small bubbles?
Bubble humidifier

76. Are bubble humidifiers heated?

77. What is the goal of a bubble humidifier?
To raise the water vapor content of a gas to ambient levels

78. What type of humidifier directs gas over a water surface?
Passover (blow-by) humidifier

79. What type of humidifier is normally used for mechanical ventilation?
Reservoir humidifier

80. What type of humidifier does not have bubbles or aerosol and has a tube coming out of the top end?
Wick humidifier

81. What type of humidifier allows vapor to pass but not water?
Membrane humidifier

82. What kind of patients use a passover humidifier?
Patients on home CPAP units or those in the neonatal nursery

83. Do passover humidifiers have high efficiency and high exposure time?
No, they have low efficiency and low exposure time.

84. How often should an HME be changed?
Every 24 hours

85. What does heat improve in bubble and passover humidifiers?
Heat improves the water output (absolute humidity).

86. Heating systems are usually used on what type of patients?
They are used on patients with bypassed upper airways and those who are receiving mechanical ventilation.

87. What risk are patients exposed to when inhaling heated gases?
Airway burns

88. How much humidity is recommended for intubated patients?
30 mg/L

89. Inhaled gas is supposed to be maintained at what temperature?
35-37 degrees C

90. What can be used to minimize the risk of inhaling condensation?
Water traps or heated circuits

91. What can cause bacterial colonization in the circuit?
The built-up of condensation

92. What are the most common devices used for bland aerosol therapy?
Large-volume jet nebulizers

93. How are large-volume jet nebulizers powered, and what are they connected to?
They are pneumatically powered and are connected directly to a flowmeter.

94. How does a large-volume jet nebulizer work?
Liquid particles are generated by passing gas at a high velocity through a small jet orifice

95. What is the optimal size for particles passing through a large-volume jet nebulizer?
2-5 micrometers

96. What device is electronically powered and uses a piezoelectric crystal to generate aerosol?
Ultrasonic nebulizer

97. Particle size is inversely proportional to what?
Signal frequency

98. Mist tents and hoods are normally used to deliver aerosol therapy to which type of patient?
Infants and children

99. What do high flows in mist tents help to do?
They help to “wash out” CO2 and reduce heat buildup.

100. What are six problems with bland aerosol therapy?
Cross-contamination and infection, environmental safety, inadequate mist production, over-hydration, bronchospasm, and noise

Final Thoughts

Understanding the roles of humidity and bland aerosol therapy in respiratory care is paramount for clinicians aiming to optimize patient outcomes.

While these therapies serve as powerful tools in airway management and clearance, their misapplication can lead to complications like hyperhydration, mucosal irritation, and even infection.

Therefore, it’s critical to weigh the benefits against potential risks and apply these treatments judiciously, often guided by specific clinical indications and contraindications.

As our grasp of respiratory physiology continues to grow, so will our ability to employ humidity and bland aerosol therapy more effectively, customizing care for each patient’s unique needs.

John Landry, BS, RRT

Written by:

John Landry, BS, RRT

John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.


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  • Mosby’s Respiratory Care Equipment. Mosby, 2017.
  • “Fundamentals of Aerosol Therapy in Critical Care.” PubMed Central (PMC), 23 Sept. 2020.
  • Kallstrom, Thomas. “AARC Clinical Practice Guideline. Bland Aerosol Administration–2003 Revision & Update.” PubMed, May 2003.
  • Graff, T. “Humidification: Indications and Hazards in Respiratory Therapy.” PubMed, 23 Sept. 1975.

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