Chapter 35 Humidity and Bland Aerosol Therapy

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Chapter 35 Humidity and Bland Aerosol Therapy

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Objectives

• Describe how airway heat and moisture exchange
  normally occur.
• State the effect that dry gases have on the
  respiratory tract.
• State when to humidify and warm inspired gas.
• Describe how various types of humidifiers work.
• Describe how to enhance humidifier performance.

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Objectives (cont.)

• State how to select and safely use humidifier
  heating and feed systems.
• Identify the indications, contraindications, and
  hazards that pertain to humidification during
  mechanical ventilation.
• Describe how to monitor patients receiving
  humidity therapy.
• Describe how to identify and resolve common
  problems with humidification systems.

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Objectives (cont.)

• State when to apply bland aerosol therapy.
• Describe how large-volume aerosol generators
  work.
• Identify the delivery systems used for bland
  aerosol therapy.
• Describe how to identify and resolve common
  problems with aerosol delivery systems.

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Objectives (cont.)

• Describe how to perform sputum induction.
• State how to select the appropriate therapy to
  condition a patients inspired gas.

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Humidity Therapy

• Physiologic control of heat-moisture exchange
• Heat-moisture exchange is the primary role of the
  upper airway.
• The nose is an effective humidifier/heater.
• The mouth is less effective.
• An artificial airway puts stress on the lower
  airway to provide heat and moisture.

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Humidity Therapy (cont.)

• Indications for humidification and warming of
  inspired gases
• Administration of dry medical gases at flows
  greater than 4 L/min.
• Following intubation of the patient
• Managing hypothermia
• Treating bronchospasm caused by cold air

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Humidity Therapy (cont.)

• Equipment
• A humidifier is a device that adds molecular
  water to gas.
• This occurs by evaporation of water from a
  surface.

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Humidity Therapy (cont.)

• Physical principles governing humidifier function
• Temperature the higher the temperature of the
  gas, the more water it can hold.
• Surface area affects the rate of evaporation.
• Contact time evaporation increases as contact
  time increases.

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Humidity Therapy (cont.)

• Types of humidifiers
• Bubble humidifiers
• Breaks an underwater gas stream into small
  bubbles
• Usually unheated
• Goal is to raise the water vapor content of the
  gas to ambient levels.

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Humidity Therapy (cont.)
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Humidity Therapy (cont.)

• Types of humidifiers (cont.)
• Passover
• Directs gas over a water surface
• Reservoir type
• Wick type
• Membrane type

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Humidity Therapy (cont.)

• Types of humidifiers (cont.)
• Heat-moisture exchangers
• Most often a passive humidifier that has been
  described as an artificial nose
• Does not add heat or water to the system
• Captures exhaled heat and moisture, which is then
  applied to the subsequent inhalation

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Humidity Therapy (cont.)

• Heating systems
• Heat improves the water output of bubble and
  passover humidifiers.
• Used primarily for patients with bypassed upper
  airways and for those receiving mechanical
  ventilation
• Heating the inhaled gas can expose the patient to
  certain risks (e.g., airway burns).

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Humidity Therapy (cont.)

• Reservoir and feed systems
• Heated humidifiers can evaporate more than 1
  L/day.
• To avoid constant refilling, the devices use
• Large water reservoir and/or
• Gravity feed system

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Humidity Therapy (cont.)

• Setting humidification levels
• At least 30 mg/L of humidity is recommended for
  intubated patients.
• Humidifiers should provide optimal levels of
  humidity in the inspired gas.
• Some experts recommend heating the inhaled gas to
  maintain airway temperatures near 35 to 37
  degrees C.

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Problem Solving and Troubleshooting

• Condensation
• Poses risks to patient and caregivers
• Can waste a lot of water
• Can occlude gas flow through the circuit
• Can be aspirated
• Problem can be minimized with use of water traps
  and heated circuits.

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Problem Solving and Troubleshooting (cont.)

• Cross-contamination
• Water in the circuit can be a source of bacterial
  colonization.
• Minimizing condensation is helpful to reduce risk
  of colonization.
• Frequently changing circuit is not needed to
  reduce chance of nosocomial infection.

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Bland Aerosol Therapy

• Bland aerosol consists of liquid particles
  suspended in a gas (oxygen or air).
• A variety of liquids may be used
• Sterile water
• Sterile saline
• hypotonic
• isotonic
• hypertonic

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Equipment for Bland Aerosol Therapy

• Large-volume jet nebulizers
• The most common device used for bland aerosol
  therapy
• Pneumatically powered and connected directly to a
  flowmeter
• Liquid particles are generated by passing gas at
  high velocity through a small jet orifice.

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Equipment for Bland Aerosol Therapy (cont.)

• Large-volume jet nebulizers (cont.)
• The low pressure at the jet draws fluid from the
  reservoir up the siphon tube
• The water is then shattered into liquid
  particles.
• The smaller particles leave the nebulizer through
  the outlet port in the gas stream.

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Equipment for Bland Aerosol Therapy (cont.)

• Large-volume jet nebulizers (cont.)
• Unheated large-volume nebulizers can produce 26
  to 35 mg H2O/L.
• Heated nebulizers can produce 35 to 55 mg H2O/L.

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Equipment for Bland Aerosol Therapy (cont.)
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Equipment for Bland Aerosol Therapy (cont.)

• Ultrasonic nebulizers
• An electrically powered device that uses a
  piezoelectric crystal to generate aerosol
• The crystal transducer converts radio waves into
  high-frequency mechanical vibrations that produce
  the aerosol.
• Particle size is inversely proportional to signal
  frequency.

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Equipment for Bland Aerosol Therapy (cont.)
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Equipment for Bland Aerosol Therapy (cont.)

• Airway appliances
• Aerosol mask
• Face tent
• T-tube
• Tracheostomy mask
• All used with large-bore tubing

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Equipment for Bland Aerosol Therapy (cont.)
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Equipment for Bland Aerosol Therapy (cont.)

• Enclosures (mist tents and hoods)
• Used to deliver aerosol therapy to infants and
  children
• Can lead to heat and CO2 buildup in tents.
• High flows through the tent help wash out CO2
  and reduce heat buildup.

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Equipment for Bland Aerosol Therapy (cont.)

• Problem solving and troubleshooting
• Problems with bland aerosol therapy are
• Cross-contamination and infection
• Environmental safety
• Inadequate mist production
• Overhydration
• Bronchospasm
• Noise

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Selecting the Appropriate Therapy