HUMIDITY AND AEROSOL

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CHAPTER 2 HUMIDITY AND AEROSOL

PRETEST QUESTIONS

Answer the pretest questions before studying the chapter. This will help you determine your strong and weak areas in the material covered.

1. Secretions tend to become thicker if the inspired air has which of the following characteristics?

A. A relative humidity of 100% at body temperature
B. 32 mg H2O per liter of gas
C. A water vapor pressure of 47 mm Hg
D. 48 mg H2O per liter of gas

2. A patient receiving 38 mg H2O per liter of gas from a nebulizer has a humidity deficit of which of the following?

A. 6 mg/L
B. 9 mg/L
C. 12 mg/L
D. 18 mg/L

3. After connecting a nasal cannula to the humidifier outlet, you kink the tubing and hear a whistling noise coming from the humidifier. Which of the following most likely has caused this?

A. The humidifier jar is cracked.
B. The capillary tube in the humidifier is disconnected.
C. The humidifier has no leaks.
D. The top of the humidifier is not screwed on tightly.

4. You notice that the patient’s secretions have become thicker and more difficult to suction since replacing the ventilator humidifier with a heat moisture exchanger. The respiratory therapist should recommend which of the following?

A. Increase inspiratory flow.
B. Increase the temperature to the heat moisture exchanger.
C. Replace with a new heat moisture exchanger.
D. Replace the heat moisture exchanger with a conventional heated humidifier.

5. Which of the following are indications for bland aerosol therapy?

1. A cough must be induced for sputum collection.
2. Mobilization of secretions must be improved.
3. Postextubation inflammation of the upper airway must be treated.
A. 1 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2, and 3

6. You notice that very little mist is being produced by a nebulizer attached to an aerosol mask. Which of the following could be responsible for this?

1. The liter flow is too high.
2. The nebulizer jet is clogged with soap residue.
3. The filter on the capillary tube is obstructed.
A. 1 only
B. 2 only
C. 1 and 3 only
D. 2 and 3 only

See answers and rationales at the back of the text.

REVIEW

I. HUMIDITY THERAPY

Note: Questions regarding humidity therapy appear on the CRT exam only.

CRT Exam Content Matrix: IIA3, IIIB8, IIIF2, IIIF2g2

A. Humidity is the quantity of moisture in air or gas that is caused by the addition of water in a gaseous state, or vapor. Also called molecular water or invisible moisture.

image The objective of humidity therapy is to make up for water loss that occurs when dry gas is delivered or when the upper airway is bypassed.

B. Clinical Uses of Humidity
1. To humidify dry therapeutic gases
2. To provide 100% body humidity of the inspired gas for patients with ET tubes or tracheostomy tubes
C. Normal Airway Humidification
1. The nose warms, humidifies, and filters inspired air.
2. The pharynx, trachea, and bronchial tree also warm, humidify, and filter inspired air.
3. By the time inspired air reaches the oropharynx, it has been warmed to approximately 34° C and is 80% to 90% saturated with H2O.
4. By the time the inspired air reaches the carina, it has been warmed to body temperature (37° C) and is 100% saturated.
5. When the inspired air is fully saturated (100%) at 37° C, it holds 44 mg H2O per liter of gas and exerts a water vapor pressure of 47 mm Hg.
D. Absolute and Relative Humidity
1. Absolute humidity is the amount of water in a given volume of gas; its measurement is expressed in milligrams per liter.
2. Relative humidity is a ratio between the amount of water in a given volume of gas and the maximum amount it is capable of holding at that temperature (capacity). Its measurement is expressed as a percentage and is obtained with a hygrometer.
3.

image

EXAMPLE:

The amount of moisture in a given volume of gas at 31° C is 24 mg H2O per liter of gas. Calculate the relative humidity. (Note: At 31°C, air can hold 32.01 mg H2O per liter.)

image

EXAMPLE:

A gas at 22°C has a relative humidity of 54%. Calculate the absolute humidity. (Note: At 22°C, air can hold 19.42 mg H2O per liter.)

image

image

E. Body Humidity
1. Body humidity is the relative humidity at body temperature and is expressed as a percentage.
2.

image

image The capacity of water at body temperature is 44 mg/L.

EXAMPLE:

If the gas that the patient is inspiring contains 21 mg of H2O per liter of gas, what is the body humidity?

image

3. A 48% body humidity indicates that the inspired air is holding only 48% of the water it takes to fully saturate the gas in the airway at body temperature. The body’s humidification system adds the other 52% by the time the air reaches the carina.
F. Humidity Deficit
1. Inspired air that is not fully saturated at body temperature creates a humidity deficit. This deficit is corrected by the body’s own humidification system.
2. Humidity deficit may be expressed in milligrams per liter or as a percentage.
3.

image

or when expressed as a percent:

image

EXAMPLE:

A patient using T-tube flow-by is inspiring air from an Ohio nebulizer that contains 18 mg H2O per liter of air. What is this patient’s humidity deficit?

image

As a percentage:

image

4. This is why it is important to deliver humidified gas at body temperature to a patient with an artificial airway that bypasses the patient’s upper airway.
5. If adequate humidity is not provided, the patient’s airway can dry out, which can lead to thickening of secretions and result in increased airway resistance.
6. Gas being delivered to a patient with an ET tube or tracheostomy tube that contains less than 44 mg H2O per liter of gas or a water vapor pressure of less than 47 mm Hg tends to dry secretions, making them thicker and more difficult to mobilize.
G. Efficiency of HumidifiersDepends on three important factors:
1. Duration of contact between the gas and water (longer duration results in increased humidity)
a. The higher the flow rate used, the less time of contact between the gas and water and therefore the lower the humidity output.
b. The lower the water level in the jar, the less time of contact between the gas and water and therefore the lower the humidity output.
2. Surface area of gas and water contact (greater surface area results in increased humidity)
3. Temperature of the gas and water (higher temperature results in increased humidity)
H. Types of Humidifiers
1. Pass-over humidifier (nonheated humidifier)

image

FIGURE 2-1

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