Humidity and Bland Aerosol Therapy refers to using mist as a treatment method for patients with a respiratory condition. It occurs in the form of water vapor and bland aerosols.

This study guide contains practice questions that cover the ins and outs of this topic. It was specifically created for Respiratory Therapy Students but other medical professionals may find it helpful as well. So if you’re ready, let’s get started.

What is Humidity Therapy?

Humidity therapy is the process of adding water vapor to an inspired gas in order to treat respiratory diseases. It’s commonly used as a method of loosening up thick mucus and secretions.

Humidity therapy can be given with or without added heat.

Humidity and Bland Aerosol Therapy (Water Vapor)

What is Bland Aerosol Therapy?

Bland Aerosol Therapy is the process of delivering liquid particles that are suspended in an inspired gas to the patient. Types of bland aerosols include:

  • Sterile water
  • Hypotonic saline
  • Isotonic saline
  • Hypertonic saline

Bland Aerosol Therapy can be given with or without oxygen therapy.

Humidity and Bland Aerosol Therapy Practice Questions:

1. What are the devices that are considered to be a humidifier?
Bubble humidifier can be prefilled or a refillable one, Passover humidifier there are three types a simple, wick, and membrane, Heat and Moisture Exchanger HME/artificial nose, and a Room Humidifier.

2. What does Humidity therapy involve?
Adding water vapor and sometimes heat to inspired gas.

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

4. Why is the mouth less effective at heat and moisture than the nose?
Because of the low ratio of gas volume to moist and warm surface area and the less vascular epithelium lining in oropharynx and hypopharynx.

5. What is ISB?
It stands for isothermic saturation boundary and is the point normally 5 cm below the carina. The temperature is 37 degrees C and it has 100% relative humidity.

6. What happens above the ISB?
Above isothermic saturation boundary, the temperature and humidity decrease during inspiration and increase during exhalation.

7. What happens below the ISB?
Below the isothermic saturation boundary, the temperature and relative humidity remain constant (BTPS).

8. What factors can shift the ISB deeper into the lungs/airways?
When a person breathes through their mouth, when they breathe cold dry air, when the upper airway is bypassed/artificial tracheal airway, or when minute ventilation is higher than normal the ISB is shifted DISTALLY.

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 humidity deficit
created when upper airway is bypassed, managing hypothermia, and treating bronchospasm caused by cold air.

11. What are the clinical signs/symptoms of inadequate airway humidification?
Atelectasis, Dry 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 are heaters used for in humidity therapy?
To prevent or treat various abnormal conditions such as hypothermia or alleviating bronchospasms.

17. What is cool humidification/bland aerosol 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 large volume nebulizers?
If secretions are thick and hard to remove or 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.

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21. How does a bubble humidifier work?
It breaks/diffuses and underwater gas stream into small bubbles, gas is directed below water level bubbles back up evaporation occurs providing humidity. The higher the flow the more humidity; the lower the flow, the lower the humidity.

22. What are the hazards 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 and flow is greater than 4 l/min or patient complains of a dry nose or irritation in the hospitals the prefilled ones are most common the refillable ones are used in home care settings for patients with oxygen concentrators.

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

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

26. What is wrong when no bubbling occurs with a bubble humidifier?
The capillary tube could be obstructed, loose connections, O2 flow may not be turned on, or 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 a pop-off valve in a bubble humidifier?
To warn of flow path obstruction and to prevent bursting of the humidifier bottle, it releases pressures greater than 2 psi.

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

30. What liter flows should be used with a bubble humidifier?
Flows of 10 L/min or less.

31. How does a wick Passover humidifier work?
It uses an absorbent material to increase the surface area for dry air to interface with heated water.

32. How does a Membrane Passover humidifier work?
It separates the water from the gas stream by means of a hydrophobic membrane causing water vapor molecules to easily pass through the membrane but blocking the liquid water/pathogens.

33. What are the advantages of the wick and membrane Passover humidifiers?
They can maintain saturation at high flow rates, they add little or no flow resistance to spontaneous breathing circuits, they do not generate any aerosols posing minimal risks for spreading infections.

34. When are Wick or Membrane Passover humidifiers used?
When a patient is on a ventilator/bypassed airways, or when need more heat to break secretions.

35. How does an HME work?
It is an artificial nose so it captures exhaled heat and moisture and uses it to heat and humidify the next inspiration it does not actively add heat or water to the system like the nose.

36. What are the hazards of an HME?
Flow resistance increases after several hours of use for some patients this may be a risk because it causes an increased work of breathing, They add 30 to 90 ml of mechanical dead space causing hypoventilation, underhydration and mucous impaction, ineffective low-pressure alarm during disconnection, mucous plugging causing hypoventilation/gas trapping, hypothermia, or mucous plugging causing increased resistive work of breathing.

37. When should an HME be used?
When upper airways are bypassed with mechanical ventilation.

38. What is the correct placement of an HME?
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 are the needed characteristics of an HME?
Stable and provides heat and moisture to the patient.

41. What are the contraindications of an HME?
Patients with thick, copious, or bloody secretions; patients with an expired tidal volume less than 70% of the delivered tidal volume; patients whose body temperature is less than 32 degrees C; patients with high spontaneous minute volumes greater than 10 l/min; and patients receiving in-line aerosol drug treatments.

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. How do Jet Nebulizers work?
They use a capillary tube to draw water and a jet to create a baffle in which water is shattered into liquid particles often larger particles will fall out smaller ones are carried to the patient.

45. When are jet nebulizers used?
When there is a presence of upper airway edema, Laryngotracheobronchitis, subglottic edema, post-extubation edema, postoperative management of the upper airway, presence of a bypassed upper airway, or need for sputum specimens or mobilization of secretions.

46. What are the hazards of the aerosol created and using jet nebulizers?
The droplets could spread infection, hazards include wheezing/bronchospasm, bronchoconstriction, overhydration, discomfort, caregiver exposure to airborne contagions produced during coughing or sputum induction, edema of the airway wall, edema because of decreased compliance and gas exchange with increased airway resistance, sputum induction with hypertonic saline can cause bronchoconstriction in patients with some pulmonary diseases.

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. What factors influence condensation?
Temperature difference across the system, ambient temperature, gas flow, set airway temp, and length, diameter, and thermal mass of breathing circuit.

52. How do you minimize condensation?
Position circuits to drain condensate away from the patient, check the circuit often, drain the excess condensate from heated humidifier breathing circuits on a regular basis, place water traps at low points in the circuit, use nebulizers placing them in a superior position, keep the circuit at a constant temperature by insulation, increasing the thermal mass, or using wire heating elements in the circuit.

53. What are the hazards of condensation?
Condensation can disrupt/occlude gas flow through the circuit altering the FiO2 or ventilation function/both, it can work its way to the patient and be aspirated.

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

55. How do you ensure heated circuits are working?
Adjust the temperature differential to the point that a few drops of condensation from near the patient connection or wye.

56. What are servo heaters?
It monitors temperature at or near the patient’s airway using a thermistor probe the controller adjusts heater power to achieve the desired airway temperature.

57. When is an ultrasonic nebulizer used?
It is used for sputum inductions when patients are unable to hack it up after trying breathing treatments of saline with large volume nebulizer.

58. When should a cool mist be delivered with large volume nebulizers?
Post-extubation stridor, inflammation of the airway/tracheal burns, croup, inflammation of Epiglottis.

59. What is the formula for relative humidity?
%RH = content/capacity x 100

60. Where is the isothermic saturation boundary (ISB)?
It is normally 5 cm below the carina. This can move up and down depending on how hard the nose has to work. The more work the nose does, the ISB moves down. The less work the nose does, the ISB moves up.

61. What happens above the ISB?
The temperature and relative humidity decrease during inspiration, and increase during exhalation.

62. What happens below the ISB?
Temperature and relative humidity remain constant.

63. When does the ISB shift dismally?
When someone breathes dry cold air, airway is bypassed, or when the minute ventilation is higher than normal.

64. What is absolute humidity?
The weight of the moisture. The amount of water in given volume of gas. It is expressed in mg/L.

65. What is relative humidity?
The ratio between the amount of water in given volume of gas and maximum amount it is capable of holding at that temperature.

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

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

68. What is a humidity deficit?
Inspired air that is not fully saturated at body temperature. Anything lower than 44mg/L.

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

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

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

72. 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 humidifier, the greater the thermal mass.

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

74. How much deadspace does an HME add?
It adds 30 – 90 mL of deadspace.

75. 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.

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

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

78. What is bland aerosol?
It consists of liquid particles suspended in a gas; sterile water and sterile saline can be used.

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

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

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

82. 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.

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

84. What kind of solution is used in sputum induction?
A 3- 10% hypersonic saline solution is used.

85. What is the primary role of the upper airway?
Heat-moisture exchange.

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

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

88. The administration of dry medical gases at flows greater than what are necessary?
Flows greater than 4 L/min. are necessary.

89. Following the intubation of a patient, it is indicated that the patient needs?
They will need humidification and warming of inspired gases.

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

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

92. When the temperature is increased, the potential humidity is?
It is also increased.

93. What type of humidifier breaks an underwater gas stream into small bubbles?
A bubble humidifier.

94. Are bubble humidifiers normally heated?
No, no they are not.

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

96. What type of humidifier directs gas over a water surface?
A passover (blow-by) humidifier.

97. What type of humidifier is normally used for mechanical ventilation?
A reservoir humidifier.

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

99. What type of humidifier allows vapor to pass, but not water?
Membrane (hydrophobic membrane)

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

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

102. What type of humidifier deals with Bernouli’s principle?
Jet humidifiers.

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

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

105. What type of humidifier is known as the “artificial nose?”
The HME.

106. What does an HME do?
They capture exhaled heat and moisture which is then applied to the subsequent inhalation (they hold the patient’s own heat and water).

107. How often is an HME changed?
Every 24 hours.

108. In bubble and passover humidifiers, heat improves what?
The water output (absolute humidity).

109. Heating systems are usually used for what type of patients?
Patients with bypassed upper airways and those on mechanical ventilation.

110. What is a risk that patients are exposed to when inhaling heated gases?
Airway burns.

111. Heated humidifiers can evaporate more than how much?
More than 1 L/day.

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

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

114. What risk due to condensation can the patient experience?
Inhalation of condensation.

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

116. What can cause a bacterial colonization in the circuit?
Built-up condensation.

117. What consists of liquid particles suspended in a gas (oxygen or air)?
Bland aerosol.

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

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

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

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

122. Unheated large-volume jet nebulizers can produce how much?
26 – 35 mg/H2O/L

123. Heated large-volume jet nebulizers can produce how much?
35 – 55 mg/H2O/L

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

125. The crystal transducer converts radio waves into what?
Into high-frequency mechanical vibrations that produce the aerosol.

126. Particle size is inversely proportional to what?
Signal frequency (frequency sound waves: 1.35-1.65)

127. Name four types of airway appliances used with large-bore tubing.
Aerosol mask, Face tent, T-tube, and Tracheostomy mask.

128. Mist tents and hoods are normally used to deliver aerosol therapy to what type of patients?
Infants and children.

129. What is one problem that Respiratory Therapists have with mist tents?
Heat and CO2 buildup.

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

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131. What are six problems with bland aerosol therapy?
Cross-contamination and infection, Environmental safety, Inadequate mist production, Over-hydration, Bronchospasm, and Noise.

132. What is bland aerosol?
Liquid particles suspended in a gas.

133. What are the factors that affect aerosol drug therapy?
Aerosol output, Particle Size, Deposition, Aging, Breathing Pattern, and Physical characteristics of the airway.

134. Particle size depends on what?
It depends on the substance that is being nebulized, the methods used to generate the aerosol, and the environmental conditions.

135. What is the optimal particle size?
1 to 5 microns

136. What is deposition?
How the particle lands. The size determines how it deposits. It’s affected by inertia, sedimentation, and brownian movement.

137. What is inertia?
Particles collide and burst resulting in rainout and less medication to the site of action. Turbulent flow can cause this.

138. What is sedimentation?
The larger the particle, the more effect gravity will have on it. This can cause rainout.

139. What is the Brownian movement?
As you breathe in, airflow slows down. Particles slow down and hit each other causing rain out.

140. What is aging?
How long the particle is suspended before it gets to the target site.

141. Aging depends on what?
The composition of aerosol, initial size of particles, time in suspension, and ambient condition which it is exposed.

141. What is an optimal breathing pattern?
Slow laminar flow with gentle, deep breaths.

142. What is absolute Humidity?
It is the actual content or weight of water present in a given volume of gas.

143. What is relative humidity?
The ratio of how much water a gas sample is actually holding.

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

145. What is the Isothermic Saturation Boundary?
At or below carina, the point where inspired gases are fully saturated and warmed to body temperature.

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

147. What does humidity therapy involve?
Adding water vapor and sometimes heat to the inspired gas.

148. What are the goals of humidity?
To reduce airway swelling, the removal of thick secretions, and to prevent the airway response to cold air.

149. What are the low flow humidifiers?
Bubble, and Jet.

150. What are the high flow humidifiers?
Heated bubble, passover, wick, vapor phase, capillary force, membrane type, and HME.

151. What does the term Inspissated refer to?
Thickening of secretions due to dehydration.

152. With prolonged breathing of improperly conditioned gases through the tracheal airway, this can result in what condition?

153. What are humidifiers used for?
To add molecular water to gases.

154. Temperature is an important factor affecting humidity due to the fact that the greater the temperature of the gas, the more what?
The more H2O vapor it will hold.

155. In order for evaporation to occur, what are the ideal conditions that need to be present?
There needs to be a large surface area to enable evaporation to take place.

156. What are the three most common humidifiers used in Respiratory care?
(1) Bubble humidifiers, (2)Passover humidifiers, and (3)Heat and moisture exchangers.

157. In the Passover humidifier, what is the purpose of the Hydrophobic membrane?
The membrane-type separates the water from the gas stream.

158. What organization sets the standards for the HME’s?
International Organization for Standardization (ISO).

159. Heated humidifiers operating continuously in breathing circuits can evaporate how much per day?
More than 1L H2O per day.

160. Simple large reservoir systems are manually refilled with sterile or distilled water. Why would this be a problem?
Because the system must be opened for refilling where cross-contamination can occur.

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

162. To maintain airway temperatures by humidification the temperature has to range between what?
35 and 37 degrees Celsius.

163. 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.

164. 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.

165. What is the definition of a Nebulizer?
A device that produces an aerosol suspension of liquid particles in a gaseous medium using baffling to control particle size.

Final Thoughts

So there you have it. That wraps up our study guide on Humidity and Bland Aerosol Therapy. This is definitely a topic to be familiar with, especially for Respiratory Therapy Students.

Hopefully, you can use this study guide (and the practice questions that are included) to make the learning process much easier. Thank you so much for reading and as always, breathe easy my friend.

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