Egan’s Chapter 35 Practice Questions:


Question Answer
Formula for Relative humidity %RH= content/capacity times 100
Where is the isothermic saturation boundary ( ISB) Normally 5cm 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
What happens above the ISB temp and relative humidity decrease during insp. And increase during exhalation
What happens below the ISB Temp. And relative humidity remain constant
When does the ISB shift dismally (farther down) When someone breaths dry cold air, airway is bypassed, minute ventilation is higher than normal
What is absolute humidity The weight of the moisture. The amount of water in given volume of gas. Expressed in mg/l
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 temp.
What is the capacity of water at body temp 44mg/lq
What is the formula for body humidity Absolute humidity/ 44mg/l times 100
What is a humidity deficit Inspired air that is not fully saturated at body temp anything lower than 44mg/l
What is the formula for humidity deficit 44mg/l-absolute humidity
What are the indications for humidification and warming of inspired gas Dry gases that are at a flow greater than 4./min, following incubation of a patient, managing hypothermia, treating bronchospasm caused by cold air.
What is a humidifier device that adds molecular water to gas, occurring by the evaporation of water from a surface
What are the factors that effect a humidifiers function Temp, the higher the temp 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
Types of humidifiers Bubble, Passover, wick, HME,cascade
How much dead space does an HME add 30-90 ml
Types of heating elements that require an electrical source Hot plate, wraparound, yolk or collar element, immersion type, heated wire- vent. circuit
What amount humidity is used for incubated patients At lease 30 mg/l
Problems with condensation Poses risk to patient and caregiver, waste water, occluded gas flow through circuit, be aspirated can be prevented with water traps. Placed at low points so its away from patient
What piece of equipment is used to measure the humidity hygrometer
What is bland aerosol Consists of liquid particles suspended in a gas, sterile water and sterile saline can be used.
How much can a unheated large volume nebulizer put out 26-35 mg h2o/l
How much can a heated large volume nebulizer put out 35-55 mg h2o/l
What is a ultrasonic nebulizer Electrically powered device that uses piezoelectric crystal to generate aerosol. Crystal transducer converts radio waves into high freq. Mechanical vibrations that produce aerosol
What does the amplitude do to the ultrasonic nebulizer Directly affects volume of aerosol output. Cannot change the frequency but you can increase the amplitude.
Types of aerosol masks Aerosol mask, trach collar, t-peice, face tent and mist hoods and tents for small children and infants
What kind of solution is used in sputum induction 3- 10% hypersonic saline solution
Question Answer
What is the primary role of the upper airway? Heat-moisture exchange
What is the most effective humidifier/heater on the body? Nose
What puts stress on the lower airway in order to provide heat and moisture? Artificial airway
Administration of dry medical gases at flows greater than 4 L/min. are necessary. True/False True
Following intubation of a patient, it is indicated that the patient needs humidification and warming of inspired gases. True/False True
What is a device that adds molecular water to gas? Humidifier
Humidifiers work by… Evaporating water from a surface.
The higher the temperature of the gas in the humidifier… The more water it can hold.
When temperature is increase, potential humidity is also increased. True/False True
Evaporation does not increase as contact time increases. True/False False (decrease the temperature of gas, the longer it takes to pass through water)
What type of humidifier breaks an underwater gas stream into small bubbles? Bubble humidifier
Are bubble humidifiers normally heated? No
The goal of a bubble humidifier is to… Raise the water vapor content of the gas to ambient levels.
What type of humidifier directs gas over a water surface? Passover (blow-by)
What type of humidifier is normally used for mechanical ventilation? Reservoir
What type of humidifier does not have bubbles or aerosol and has a tube coming out the top end? Wick
What type of humidifier allows vapor to pass, but not water? Membrane (hydrophobic membrane)
What kind of patients use a Passover humidifier? Patients on home CPAP units/neonatal nursery
Passover humidifiers have a high efficiency and high exposure time. True/False False (low efficiency/low exposure time)
What type of humidifier deals with Bernouli’s principle? Jet
What is Bernouli’s principle? When gas in a tube exerts lateral wall pressure due to the gas velocity
What type of humidifier uses a filter? Heat-moisture exchangers (HME)
What type of humidifier is known as the “artificial nose?” HME
HMEs do not add heat or water to the system. True/False True
What does an HME do? Captures exhaled heat and moisture which is then applied to the subsequent inhalation (holds patient’s own heat & water)
How often is an HME changed? Every 24 hours
In bubble and passover humidifiers, heat improves… The water output (absolute humidity)
Heating systems are usually used for what type of patients? Patients with bypassed upper airways and those on mechanical ventilation
What is a risk that patients are exposed to when inhaling heated gases? Airway burns
Heated humidifiers can evaporate more than… 1 L/day
To avoid constant refilling, large water reservoirs and gravity feed systems exist. True/False True
How much humidity is recommended for intubated patients? 30 mg/L
Inhaled gas is supposed to be maintained at… 35-37 degrees C
Condensation does not pose any risks to patient/caregivers. True/False False (it does)
Condensation can waste lots of water. True/False True
Condensation can block gas flow through the circuit. True/False True
What risk due to condensation can the patient experience? Inhalation of condensation
What can be used to minimize the risk of inhalation of condensation? Water traps or heated circuits
What does VAP stand for? Ventilator acquired pneumonia
What can cause a bacterial colonization in the circuit? Built-up condensation
Minimizing condensation can help to reduce OR achieve the risk of bacterial colonization? Reduce
What consists of liquid particles suspended in a gas (oxygen or air)? Bland aerosol
What are the most common devices used for bland aerosol therapy? Large-volume jet nebulizers
How are large-volume jet nebulizers powered? What are they connected to? Pneumatically powered; directly to a flowmeter
How does a large-volume jet nebulizer work? Liquid particles are generated by passing gas at high velocity through a small jet orifice.
What is the optimal size for particles passing through the large-volume jet nebulizer? 2-5 micrometers
0.25 – 1.0 micro meters: minimal settling in the lungs 1.0 – 2.0 micro meters: enter alveoli 2.0 – 5.0 micro meters: deposit/settle to alveoli 5.0 + micro meters: too big to enter airway True/False True
Unheated large-volume jet nebulizers can produce… 26 to 35 mg/H2O/L
Heated large-volume jet nebulizers can produce… 35 to 55 mg/H2O/L
What device is electronically powered and uses a piezoelectric crystal to generate aerosol? Ultrasonic nebulizer
The crystal transducer converts ______________________ into high-frequency mechanical vibrations that produce the aerosol. radio waves
Particle size is inversely proportional to… Signal frequency (frequency sound waves: 1.35-1.65)
Name four types of airway appliances used with large-bore tubing. Aerosol mask Face tent T-tube Tracheostomy mask
Mist tents and hoods are normally used to deliver aerosol therapy to what type of patients? Infants and children
Name one problem that RTs have with mist tents. Heat and CO2 buildup
What do high flows in mist tents help to do? “Wash out” CO2 and reduce heat buildup
Name six problems with bland aerosol therapy. Cross-contamination and infection Environmental safety Inadequate mist production Over-hydration Bronchospasm Noise




1. List all devices considered a humidifier?
2. What does Humidity therapy involve?
3. Heat and Moisture exchange is a primary function of what?
4. Why is the mouth less effective at heat and moisture than the nose?
5. What is ISB?
6. What happens above the ISB?
7. What happens below the ISB?
8. What factors can shift the ISB deeper into the lungs/airways?
9. What is the primary goal of humidification?
10. What are the indications for humidification therapy?
11. What are the clinical signs/symptoms of inadequate airway humidification?
12. What is absolute humidity?
13. What is relative humidity?
14. What is body humidity?
15. What is the expected body humidity value at normal body temperature?
16. What are heaters used for in humidity therapy?
17. What is cool humidification/bland aerosol used for?
18. How does a heater improve the effectiveness of a humidifier?
19. Study box 35-4 for heater guidelines
20. What are the four variables that affect the performance of a humidifier?

21. How does a bubble humidifier work?
22. What are the hazards of using a bubble humidifier?
23. When should a bubble humidifier be used?
24. What problems could be wrong with a bubble humidifier if no sound is heard when pinching the tubing?
25. What is wrong if the bubble humidifier whistles by itself?
26. What is wrong when no bubbling occurs with a bubble humidifier?
27. What are the factors that influence the output of a bubble humidifier?
28. What is the purpose of a pop off valve in a bubble humidifier?
29. What is the expected water vapor output of bubble humidifier?
30. What liter flows should be used with a bubble humidifier?
31. How does a wick Passover humidifier work?
32. How does a Membrane Passover humidifier work?
33. What are the advantages of the wick and membrane Passover humidifiers?
34. When are Wick or Membrane Passover humidifiers used?
35. How does an HME work?
36. What are hazards of an HME?
37. When should HME be used?
38. What is the correct placement of an HME?
39. What are the three types of HMEs?
40. What are the needed characteristics of an HME?
41. What are the contraindications of an HME?
42. How can you tell if the HME is working properly?
43. When should HME be changed to a large volume nebulizer with a heater?
44. How do Jet Nebulizers work?
45. When are jet nebulizers used ?
46. What are the hazards of the aerosol created and using jet nebulizers?
47. What is the purpose of a room humidifier?
48. How does a room humidifier work?
49. What is a hazard of a room humidifier? Read sheet paragraph bout room humidifiers
50. How does condensation occur?
51. What factors influence condensation?
52. how do you minimize condensation?
53. What are the hazards of condensation?
54. How is condensation disposed?
55. How do you ensure heated circuits are working?
56. What are servo heaters?
57. study page 834
58. study 839
59. When is an ultrasonic nebulizer used?
60. What are the hazards of ultrasonic nebulizer?
61. When should a cool mist be delivered with large volume nebulizers?
62. When should heat be delivered with large volume nebulizers?
63. Study box 35-5 page 837
64. What are the symptoms of humidity deficit?
65. What is the formula for relative humidity?
66. What is the formula for body humidity?
67. What is the formula for humidity deficit?
68. What is the formula for Absolute humidity?




1. 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. Adding water vapor and sometimes heat to inspired gas

3. the upper respiratory tract, mainly the nose

4. 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. It stands for isothermic saturation boundary this is the point normally 5 cm below the carina temperature is 37 degrees C and 100% relative humidity

6. Above isothermic saturation boundary the temperature and humidity decrease during inspiration and increase during exhalation

7. Below the isothermic saturation boundary the temperature and relative humidity remain constant (BTPS)

8. 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. To maintain normal physiologic conditions in the lower airways

10. 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. 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. the actual amount of moisture contained in a gas

13. the amount of water vapor a sample could maximally hold at a given temperature

14. the amount of water vapor in a gas sample compared to the capacity for water vapor at body temperature

15. 44 mg/l

16. To prevent or treat various abnormal conditions such as hypothermia or alleviating bronchospasms

17. Upper airway inflammation from croup, epiglottitis, and postextubation edema

18. Heat improves the water output of humidifiers

19. Study box 35-4 for heater guidelines

20. Temperature, surface area, time of contact, and thermal mass

21. 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 less the flow less humidity

22. At a high flow rate it can produce aerosols which can transmit pathogenic bacteria from the humidifier reservoir to the patient

23. 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. 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. The O2 flow may be too high or the tubing may be kinked/obstructed

26. Capillary tube could be obstructed, loose connections, O2 flow may not be turned on, or inadequate pressure in the line

27. Temperature, Relative humidity , and absolute humidity

28. To warn of flow path obstruction and to prevent bursting of the humidifier bottle, it releases pressures greater than 2psi

29. 80%

30. Flows 10 l/min and less

31. It uses an absorbent material to increase the surface area for dry air to interface with heated water

32. 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. 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 patient is on a ventilator/bypassed airways or when need more heat to break secretions

35. 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. 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 upper airways are bypassed and mechanical ventilation

38. 10cm away from endotracheal tube and proximal to the ventilator circuit

39. Simple (high thermal conductivity) Condenser humidifier, Hygroscopic (low thermal conductivity) Condenser humidifier, and Hydrophobic (water repellent element) Condenser humidifier

40. Stable and provides heat and moisture to the patient.

41. 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. If the patient is receiving proper heat and moisture.

43. When secretions can’t be broken up

44. 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 there is presence of upper airway edema, Laryngotracheobronchitis, subglottic edema, postextubation edema, postoperative management of the upper airway, presence of a bypassed upper airway, or need for sputum specimens or mobilization of secretions

46. of the aerosol it is the droplets which 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 bc 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. To help with sinusitis and drainage

48. it creates an aerosol that exits the device and evaporates in the ambient air increasing the humidity of the room

49. it is a potential source of nosocomial infections (read sheet paragraph bout room humidifiers)

50. 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. temperature difference across the system, ambient temperature, gas flow, set airway temp, and length, diameter, and thermal mass of breathing circuit

52. 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. 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. it is treated as infectious waste and therefore drained into an infectious waste container

55. Adjust the temperature differential to the point that a few drops of condensation form near the patient connection or wye

56. 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. study page 834

58. study 839

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

60. bronchospasm – stop and deliver bronchodilator, fluid overloads – limit treatment time or try something else, mucus plugging and occlusion of airway – encourage cough suction if need to

61. post extubation stridor, inflammation of the airway/tracheal burns, croup, inflammation of Epiglottis

62. if secretions are thick and hard to remove or the patient’s upper airway is bypassed