Review of HumidityAerosol Therapy

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Review of Humidity-Aerosol Therapy

• RsCr 224
• Respiratory Care Theory 2

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Definitions of Esssential Terms

• Absolute Humidity - amount of water vapor
  actually present in the air (expressed in
  mg/liter). Sometimes called water vapor content.
• Maximum Absolute Humidity - amount of water vapor
  that the air can hold. Sometimes called water
  vapor capacity.
• varies directly with temperature
• Relative Humidity - the mathematical comparison
  of the above two. Content divided by capacity

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Essential Information for Doing Calculations of
Relative Humidity

• The Maximum Absolute Humidity at body temperature
  is 44 mg/liter
• This is sometimes called Body Humidity
• Any Relative Humidity less than Body Humidity is
  called the Humidity Deficit

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ANSI Guidelines

• 10 mg/L for Normal patient
• 30 mg/L for intubated patients

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Indications for Humidifying and Warming of Gases

• To humidify dry inspired gases
• To overcome the humidity deficit when the upper
  airway is bypassed (trached patients or those
  with endotracheal tubes)
• Less common indications
• treatment of hypothermia
• treatment of bronchospasm caused by cold air

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Equipment Used to Humidify Gases

• Bubble Diffusion Humidifiers

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Factors Affecting Performance of Bubble
Humidifiers

• Time of contact between gas the water
• Surface area available for evaporation to occur
• Temperature of the gas

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How Flow Lowers Water Temp
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Typical Wick Type Humidifier
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Fisher-Paykel Wick Humidifier
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Puritan-Bennett Cascade 1
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Puritan-Bennett Cascade 2
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Hudson-RCI Conchatherm
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Characteristics of Heated Humidifiers

• Water can be heated to maintain high humidity
  output
• Temperature can be sensed downstream from the
  unit so that water temperature can be adjusted to
  maintain correct gas temperature (like thermostat
  at home)
• Heated wires can be employed to prevent
  condensation in tubing from gas cooling

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Why Wick Type Humdifiers Are Popular

• Produce high vapor output even at very high gas
  flows (gt100 l/m)
• Do not produce any water particles
• Low risk of producing nosocomial infections
• Have ability to utilize heated wire circuits
• Have continuous-feed water systems

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Hazards Problems Associated with Heated
Humidifiers

• Overheating leading to patient airway burns
• Inadvertent overfilling of humidifier by
  therapist
• Increased airway resistance created by pooling of
  condensate in circuit
• Burns to caregivers from inadvertently touching
  heated metal surfaces

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Artificial Noses

• Types of Heat Moisture Exchangers
• Simple condensors
• Hygroscopic Condenser Humidifiers (HCF)
• Hydrophobic Condenser Humidifiers
• Act by recycling exhaled heat moisture
• Ideal unit should be able to produce at least
  30 mg/l - Most produce 20 - 30 mg/l

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Problems With HMEs

• Increase in airflow resistance (particularly when
  mucus enters unit)
• Drying thickening of secretions can become a
  problem
• Must be removed when administering in-line
  medication aerosol treatments
• Lose efficiency in patients with high minute
  volumes (gt10 l/m)

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Why HMEs Have Become Popular?

• Significant cost savings can be realized compared
  to a standard ventilator circuit using a heated
  humidifier
• Less therapist time needed to drain condensed
  water from circuit
• Greater simplicity
• However, in some cases heated-wire circuits may
  be actually cheaper than the HME

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Bland Aerosol Therapy

• Indications for
• Tx of laryngotracheobronchitis (croup)
• Tx of sub-glottic edema
• Post-extubation edema
• Post-operative management of upper airway
• Presence of bypassed upper airway
• Need for sputum induction

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Contraindications to Bland Aerosol Therapy

• Bronchospasm (evidence of current disease)
• Asthma or Chronic Bronchitis patients who c/o
  SOB
• History of airway hyperresponiveness
• Those with a hx of asthma or other obstructive
  lung disease

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Hazards and Complications of Bland Aerosol

• Wheezing associated with bronchospasm
• Infection
• Overhydration
• Patient discomfort
• Caregiver exposure to contagious aerosols
• Noise

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Types of Nebulizers Used for Bland Aerosol Therapy

• Large Volume Jet Nebulizers
• Ultrasonic Nebulizers

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Schematic of Large Volume Jet Nebulizer
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Schematic of Ultrasonic Nebulizer (USN)
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Solutions Used for Bland Aerosol Therapy

• Water - most irritating cheapest to use
• Normal Saline (0.9 NaCl) - least irritating
  salt crystals can condense on water intake
  causing no aerosol to be produced
• Hypertonic Saline - 5 or 10 - used only for
  sputum indutions

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Delivery of Inhaled Medications

• Delivery systems
• MDIs
• DPIs
• Small volume jet nebulizers
• aka HHNs SVNs wet nebs med nebs neb meds
  acrons
• USNs
• Specialized aerosol systems

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Definitions

• Aerosol
• Penetration
• Deposition
• Stability
• Retention
• Clearance

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Factors for Penetration and Deposition

• Size of particle decides how far before
  depositing into the respiratory tract

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Indications for aerosols

• Deliver medications
• Humidify gases
• Mobilize secretions

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Hazards

• Overhumidification
• Bronchospasm
• Infection

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Examples of MDIs
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Characteristics of MDIs

• Exact same dose each actuation
• High initial aerosol velocity
• Currently uses chloroflourocarbon (CFC)
  propellant. Hydroflouroalkanes (HFA) will
  replace CFCs pending final approval.
• Without using a spacer - up to 80 of aerosol
  lands in the oropharynx or mouth
• 10 - 20 reaches small airways
• administration is very technique dependent

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MDI Accessory Devices

• Holding chambers or spacers
• Improve ease of administration
• Decrease oral-pharyngeal deposition
• Improve distribution of the mist
• Flow-triggered MDIs
• Currently only Maxair (pirbuterol) is available

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Optimal Technique for Using MDI

• Shake MDI first (warm if cold)
• Actuate into chamber
• Inhale slowly deeply
• Maintain a 10 second breath hold
• Allow 30 seconds between actuation

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Disadvantages of MDIs

• Coordination can be a problem
• Requires use of additional spacer
• High oral-pharyngeal deposition
• Easy for patients to overuse
• Some medications can be quite expensive
• Some patients can run out without realizing

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Characteristics of DPIs

• Always are breath actuated since no propellant is
  used
• Easier to self-administer - no spacer needed
• Not very many drugs are available in this form
• At least as good as MDI in terms of deposition
  and drug response
• Cant be used with young children in ventilator
  circuits

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Brand Names

• Rotahaler Albuterol
• Spinhaler Intal
• Turbuhaler Terbutaline
• Advair Flovent and Salmeterol

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Optimal Technique for Using DPI

• Patient must use high inspiratory flows
• Best not used if patient is having severe SOB
• Breath holding is not critical
• Medication should be stored in a low humidity
  environment

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Disadvantages of DPIs

• Some patients cant generate high inspiratory
  flows needed
• Assembly of unit can be difficult for some
• Difficult to give high doses
• Some pharyngeal deposition is unavoidable
• Not that many medications available in this form
  (currently)

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Small Volume Nebulizers

• Generally hold 2 - 6 ml of solution
• Can be filled using unit-dose preparations or
  multi-dose vials
• Generally require 4-8 l/m of flow to actuate
• Can be driven with either oxygen or air
• When using oxygen - FIO2 can be 40 - 90 !!
• Should be used instead of MDI or DPI if patient
  is tachypneic

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Disadvantages of SVNs

• Too complex for some patients to use
• Requires assembly periodic cleaning
• Not easily portable like the MDI or DPI
• Not all medications are available
• No steroids currently available for SNV
  administration

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Specialized Medication Nebulizers

• Respigard II - filters exhaled gas - delivers
  very small particles (1-2 microns)
• Circulair - Uses a reservoir bag to conserve
  medication - enhances aerosol delivery
• Continuous HEART Nebulizers - used for
  continuous drug administration (1-3 hours)
• SPAG unit- used for administration of ribavirin

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Small Volume Ultrasonic Nebulizers

• Produce very dense mists at very high outputs
• Compact units portable easy to use
• Used for delivery of undiluted medications
  (bronchodilators antibiotics)
• Some units can be powered by cigarette lighter
  adapter present in a car

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Problems with USNs

• Expensive to purchase
• Prone to breakdown
• Not all mediations are available in multi-dose or
  unit dose forms
• Medication must be manually added to unit prior
  to use

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The End

• Thats all folks