For which of the following patients might you recommend bland aerosol therapy administration?

Key Terms

Aerosol

Condensation

Inspissated

Humidifier

Water trap

The primary function of the upper respiratory tract is to heat and humidify the air we breathe. Clinical signs and symptoms of inadequate airway humidification may be noticed during routine patient assessment or reported by a patient as dryness of the nose or cough (Box 13-1). With numerous devices available, the respiratory therapist (RT) must be knowledgeable about how these devices work to be able to administer therapy to patients in the most appropriate and effective ways.

Determination of the most appropriate way to condition a patient’s inspired medical gas requires patient assessment and evaluation of the goal of the therapy. An algorithm to assist in selecting the appropriate humidification delivery device is provided in Figure 13-1. This chapter will cover pertinent information relating to the equipment and clinical applications of humidification and bland aerosol therapy. Use of small-volume nebulizers for medication delivery will be covered in Chapter 19.

With the nose being the main participant in the process of filtering, heating, and humidifying inspired air, the additional flow of supplemental oxygen may impede its effectiveness. Humidification of oxygen is indicated for flow rates over 4 L/min. However, if the patient is complaining or displaying signs or symptoms of inadequate humidification, any amount of flow should be humidified. Bubble humidifiers should be used with oxygen flow rates under 10 L/min. The following is the step-by-step process for using a bubble humidifier.

Frequently, in the presence of infection, airway adjunct use, or exacerbation of a respiratory pathology, patients will require bland aerosol therapy. Their secretions may become inspissated, or thickened, because of dehydration. The most common device used to deliver this therapy is a large-volume nebulizer. Images of large volume nebulizers are provided in Figure 13-2.

A heater may also be included in the system, if required. When heating inspired gas, a water trap system should be incorporated to trap condensation, the change of state from gas to liquid, also called “rain-out.” Figure 13-3 illustrates a water trap system. Water in the circuit may alter the FiO2 being delivered, is an aspiration risk to the patient, and poses an infection risk to both the patient and the caregiver.

The following is the step-by-step process for using a large-volume nebulizer.

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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?
80%

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