Egan's Chapter 39: Humidity & Bland Aerosol

Room temperature: 72 degrees

Mouth Temperature: 72 degrees

What is the relative humidity of the mouth and nose?

50% RN

As it goes through the 3 chambers RH goes up to about 90%

* Most humidity occurs in the nasal muscous

Hypopharynx --> ISB is 5% of the humidity

What is the role of the nose?

Nose heats and humidifies gas on inspiration and cools and reclaims water from gas that is exhaled

BTPS conditions

Body temperature at 37º C; barometric pressure; saturated with water vapor [100% relative humidity at 37º C]

Normally about 5 cm below carina is isothermic saturation boundary (ISB)

Heat and moisture exchange is the primary role of the...

upper airway, mainly the nose

Relative humidity

- Amount of water vapor in the air, expressed as a % of amount needed for saturation at the same temperature

- Expressed as percentage and is obtained with hygrometer

RH equation

Relative humidity = absolute humidity capacity (content/capacity) × 100

Absolute humidity

Amount of water in given volume of gas; its measurement is expressed in mg/L

Body Humidity

- Capacity of water at body temperature is 44 mg/L

- Body humidity = absolute humidity/ 44 mg/L × 100

Humidity deficit

Inspired air that is not fully saturated at body temperature

Humidity deficit = 44 mg/L - absolute humidity

What physical principles govern humidifier fxn?

temperature, surface area, time of contact, thermal mass

How does temperature govern humidifier fxn?

the higher the temp of gas, the more water it can hold

How does surface area govern humidifier fxn?

1. affects rate of evaportion

2. The greater the area of contact between water and gas, the more opportunity there is for evaporation to occur

3. Passover humidifiers pass gas over a large surface area of water

How are bubble-diffusion and the physical principles of governing humidifier relate?

It involves surface area

- Bubble-diffusion directs a stream of gas underwater, where it is broken up into small bubbles

How does time of contact effect the governing of humidifier fxn?

evaporation will increase as contact time increases

- For bubble humidifiers, contact time depends on the depth of the water column

- In passover and wick-type humidifiers, the flow rate of gas through the humidifier is inversely related to contact time

How does thermal mass effect the governing of humidifier fxn?

the greater the amount of water in humidifier, the greater the thermal mass and capacity to hold and transfer heat to therapeutic gas

Indications for Humidification Therapy: Primary

1. Humidifying dry medical gases

2. Overcoming humidity deficit created when upper airway is bypassed

Indications for Humidification Therapy: Secondary

Treating bronchospasm caused by cold air

Cool dry air can also cause an asthma exacerbation

Define and differentiate hydrophobic and hygroscopic

o Hydrophobic

1. "water hating"

2. Little or no tendency to absorb water

3. Typically have a nonpolar surface that replaces water

4. Water vapor passes through the pores in the membranes but liquid waterand pathogens cannot

o Hygroscopic

1. Water absorbing

2. Materials absorb moisture from the air

Define inspissated

A thickened and dried, owing to dehydration, occurs when the airway is exposedto relatively cold dry air, ciliary motility is reduced, airways become moreirritable, and mucus production increases.

Describe the isothermic saturation boundary

o 37 C, 100% relative humidity

o Normally approximately 5 cm below the carina

At body temperature, gas has a saturated capacity of about 44 mg of water vapor per liter. If a gas has an absolute humidity of 22 mg/L, what is the relative humidity?

Formula:

Solution:

Answer:

Formula: RH = content/capcity * 100%

Solution:(22/44) 100 = 0.5 100 = 50%

Answer: 50%

What is an active HME?

An active HME adds humidity/heat to the inspired gas, this is done by chemicalor electrical means.

List the four variables that affect the quality of performance of a humidifier.

o Temperature

o Surface area

o Time of contact

o Thermal masses

List two indications for humidification.

o Bypass of upper airway

o Humidifying dry medical gases

Explain inspiration and exhalation as they relate to how gas is heated and humidified under normal conditions

In: The contact between the inspired air and the mucosa is increased as thegas travels through the turbinate --> inspired gas enters the nose --> warmsup and absorbs water vapor from the moist mucosal lining --> cooling themucosal surface.

Ex: Heat from expired gas is transferred back to the trachea and mucosathrough convection.

List 4 indications for bland aerosol administration

o Presence of upper airway edema

o Presence of a bypassed upper airway

o Subglottic edema

o Laryngotracheal bronchitis

Identify the two primary clinical problems associated with tents and body enclosures (like a hood)

o CO2 buildup

o Heat retention

A respiratory therapist hears a loud whistling sound as she enters the room of a patient receiving oxygen via nasal cannula at 6 L/min. In reference to the humidifier, what is the most likely cause of the problem?

A. The top of the humidifier is cross threaded

B. There is a kink in the oxygen supply tubing

C. The humidifier has ran out of water

D. The flow rate is set at less than the ordered amount

B. There is a kink in the oxygen supply tubing

An ultrasonic nebulizer is ordered for sputum induction. Which of the following solutions should be placed in the medication cup to accomplish this goal?

A. 0.9% NaCl solution

B. 3% NaCl solution

C. Sterile distilled water

D. 0.45% NaCl solution

B. 3% NaCl solution

A large volume nebulizer is set at an FiO2 of 0.40 and a flow rate of 10 L/min to deliver humidified oxygen to a patient with a tracheostomy. The nebulizer is producing very little mist. Which of the following could be done to improve the aerosol output?

I. Check the water level in the nebulizer

II. Increase the flow rate to the nebulizer

III. Drain condensate from the supply tubing

IV. Turn off the nebulizer's heating system

I & III

While performing a ventilator check, the RT observes a large amount of thin, whit mucus in the tubing connected to the HME. Which of the following actions should be taken at this time?

A. Place the patient on a heated humidification system

B. Rinse out the HME with sterile water

C. Replace the HME

D. Suction the mucus from the tubing

C. Replace the HME

Device that adds invisible molecular water to gas:

Humidifier

Generates and disperses particles into the gas stream

Nebulizer

The most important factor affecting humidifier output:

Temperature

At body temperature, gas has a saturated capacity of about 44 mg of water vapor per liter. If a gas has an absolute humidity of 22 mg/L, what is the humidity deficit?

A. 3 mg/L

B. 11 mg/L

C. 33 mg/L

D. 22 mg/L

D. 22 mg/L

Bubble humidifiers are added to what type of oxygen delivery system?

A. low flow systems, such as a nasal cannula

B. simple masks

C. high flow systems, such as venturi mask

D. aerosol nebulizers

A. low flow systems, such as a nasal cannula

What safety device is incorporated into the design of a bubble humidifier?

A. A caverning spicule

B. A pop-off valve

C. A molecular "seat belt"

D. A dog whistle

B. A pop-off valve

Active humidifier:

actively adding heat or water or both to the device-patient interface

Typically include: Bubble humidifiers (does not heat), passover humidifiers (does heat), nebulizers of bland aerosols, and vaporizers

Passive humidifier:

recycling exhaled heat and humidity from the patient

Passive humidifiers refer to typical heat and moisture exchangers (HMEs)

Active Humidifier: Bubble humidifier

- Usually used unheated with oxygen delivery systems to raise water vapor content of gas to ambient levels

•Low flow

- Can produce aerosols at high flow rates

•Poses risk of infections

- Unheated bubble humidifiers can provide absolute humidity levels between approximately 15 mg/L and 20 mg/L

Active Humidifier: Passover

Directs gas over water surface

*Simple reservoir type (heating element)

1.Flow of gas goes across and is pushes towards patient

2.Is used after 48 hours and heat and moisture system is removed

Passover: advantages over bubble humidifier

•Maintains saturation at high flow rates

•Add little or no flow resistance to spontaneous breathing circuits

•Do not generate any aerosols that can spread infection

Passive humidifiers: Heat-moisture exchangers (HMEs)

- Often passive humidifier that has been described as "artificial nose"

- Captures exhaled heat and moisture and returns up to 70% of the heat and humidity to the patient during the next inspiration

- HMEs add 5-90 ml of dead space

Type of HME: Simple condense humidifiers

•Contain a condenser element with high thermal conductivity, usually consisting of metallic gauze, corrugated metal, or parallel metal tubes

Type of HME: Hygroscopic condenser humidifiers

•Use materials that (1) incorporate a condensing element of low thermal conductivity (e.g., paper, wool, or foam) and (2) impregnating this material with a hygroscopic salt

Type of HME: Hydrophobic condenser humidifiers

•Use a water-repellent element with a large surface area and low thermal conductivity

Setting Humidification Levels: At least _______ of humidity is recommended for intubated patients.

30 mg/L

Setting Humidification Levels: some experts recommend heating inhaled gas to maintain airway temperatures near ____ to ____.

35 C to 37 C

The current AARC Clinical Practice Guideline recommends _____ degrees C within _____ degrees C, with a minimum of ____ of water vapor.

33 C within 2 C with a minimum of 30 mg/L of water vapor

Problem Solving and Troubleshooting: Condensation

1. Poses risks to patient and caregivers

2. Can waste a lot of water

3. Can occlude gas flow through circuit

4. Can be aspirated

5. Loses temperature as humidity moves from point A --> point B

Bland aerosol consists of __________ suspended in _____________.

liquid particles suspended in gas (oxygen or air)

Bland Aerosol therapy: liquids that may be used

1.Sterile water

2. Sterile saline

•Hypotonic

•Isotonic

•Hypertonic (3%-7%)

-->Cystic fibrosis à loses salinity in lungs

-->This saline helps restore salinity in lungs

-->Helps cough up mucus à use for culture & sensitivity test

Bland Aerosol Therapy: Indications

1. Presence of upper airway edema—cool, bland aerosol

•EX: trachea

2. Laryngotracheobronchitis

3. Subglottic edema

4. Postextubation edema

5. Postoperative management of the upper airway

•Subglottic or upper airway edema

6. Presence of a bypassed upper airway

7. Need for sputum specimens or mobilization of secretions (check blood and urine)

•Give hypertonic saline to help cough and obtain a sputum culture

bland aerosol therapy contraindications

- Bronchoconstriction

- History of airway hyperresponsiveness

- Twitchy airways

Bland Aerosol Therapy: Hazards and Complications

- Wheezing or bronchospasm

- Infection

- Overhydration

- Patient discomfort

- Caregiver exposure to airborne contagions produced during coughing or sputum induction

- Edema of the airway wall

Proper conditioning of inspired gas:

- Regularly measuring patients' inspired FiO2 levels

- Providing ventilatory care and monitoring selected pressures, volumes, and flows

- Using hygrometer-thermometer system

what happens if humidity is too high

heating and cramps- electrolyte imbalance

heat stroke 

what is syncope

rapid increase or decrease in BP or HR

what is inspissated

thickened, dehydrated secretions