Humidity Therapy

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Humidity Therapy

• Indications for humidity therapy
• Physiologic importance of humidity
• Types of humidifiers

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Humidifiers

• Add water vapor to inspired gas.
• Indications
• Make oxygen therapy more comfortable to upper
  airway
• Prevent a humidity deficit if upper airway
  by-passed
• Aerosol devices may also be used as humidifiers

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Importance of Upper Airway

• Filters ( particles down to 5 microns in
  diameter)
• Vibrissae
• Cilia (posterior 2/3 rds nasopharynx)
• Warms
• capillaries
• Adds water vapor
• mucus layer

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Normally gas inspired through Upper Airway

• 100 Relative Humidity at 33 o by the time gas
  reaches the carina
• 100 Relative Humidity at 37 o at segmental
  bronchi

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Isothermic saturation boundary
Irlbeck D. Normal mechanisms of heat and moisture
exchange in the respiratory tract. Respiratory
Care Clinics of North America. 1998 4(2) 189-198.
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Lower Airway

• Not as efficient in humidifying inspired gases
• 2 primary differences between upper and lower
  airways
• Upper airway nasal capillaries have fenestrations
  like a soaker hose for the active transport of
  water.
• Counter-current blood flow maintains gas
  temperature in the nasopharynx

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Filtering by Lower Airway

• Primary function of mucociliary escalator -
  called pulmonary clearance.
• Mucociliary escalator two components
• mucus
• cilia

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Mucus Layer

• 2 layers
• Sol or watery layer surrounds cilia
• Gel or mucus layer rides on top
• Mucus produced by submucosal glands and surface
  goblet cells.
• SG outnumber GC 40 1 in trachea and bronchi
• Fewer SG beyond level of bronchi
• GC exist throughout respiratory tract
• Mucus 95 water and 5 mucins (glycoproteins)

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Cilia

• Approximately 200 cilia per epithelial cell
• Beat 1500/min
• Move mucus blanket about 2 mm/min - takes about
  1 hour for mucus blanket to move from carina to
  pharynx
• Ratio of ciliated cells to goblet cells 51

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Mucociliary Escalator

• Ends at terminal bronchioles
• Alveoli cleared of foreign particles by alveolar
  macrophages

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If upper airway by-passed

• Lower airway must filter, warm and humidify
  inspired gases
• Mucociliary escalator is impaired
• Sol layer dries out
• Cilia unable to beat
• Secretions arent cleared - airways blocked
• Foreign particles (microbes) trapped on mucus
  blanket start to multiply

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Types of Humidifiers

• Unheated humidifiers
• Bubble
• Makes O2 Tx more comfortable to upper airway
• Heated humidifers
• Bubble/diffuser, wick, passover
• Prevents humidity deficit if upper airway
  bypassed
• Heat Moisture Exchangers (HME)

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When to add Bubble Humidifier to Oxygen Delivery
Device

• Oxygen from cylinder or wall outlet bone dry
• Humidify oxygen from low flow devices if
• nasal cannula gt 4 LPM
• all low flow masks
• High flow devices
• Venti mask on higher FIO2 scale
• APN and GIN are aerosol devices

http//www.rcjournal.com/online_resources/cpgs/ota
chcpg-update.html
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Heated Humidifiers

• Use when Upper Airway Passed
• Endotracheal tube
• Tracheostomy tube
• Prevents humidity deficit

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Humidity Deficit

• 44 mg/L water vapor
• inspired water vapor
• humidity deficit (mg/L) at
• 37 o C

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With Artificial Airways (ETT and Tracheostomy
Tubes)

• Upper airway bypassed
• Lower Airway must make up humidity deficit
• Causes mucosal drying and mucus plugging
• Reason why humidifier must provide 100 RH at 32
  - 34 o C

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Body Humidity 44 mg water vapor / Liter gas

• 100 saturated with water vapor
• 37o C

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Relative Humidity

• Actual water vapor Content
• Capacity

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Capacity of gas to hold water vapor determined by
gas temperature
Potential Humidity Table

• Vapor Pressure

35
25
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Temperature
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What is the water vapor content of 50 RH at 20o
C?
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50 RH at 20o C

• Capacity 20o C 17.30 mg/L
• Content .50
• 17.30
• 17.30 x .5 8.65 mg/L

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What is the Body Humidity?

• Inspired gas contains 8.65 mg/L water vapor
• Body Humidity ?

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Body Humidity

• content / 44 mg/L BH
• 8.65 20 body humidity

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If Upper Airway Bypassed

• Heated Humidifier
• Inspired gas temperature at mouth 32 - 34o C

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Humidifiers Increase the Rate of Evaporation
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Evaporation

• Define
• Requires energy in the form of heat.
• Latent heat of evaporation

Co
steam
539 cal
100
Vaporizing
water
Melting
0
ice
calories
744
205
105
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Heat added
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Factors that Increase the Rate of Evaporation

• Increased surface area of gas/liquid interface
• Decreased surface vapor pressure
• Agitation
• Heat

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Humidifiers

• Unheated
• Bubble
• Heated
• Bubble/diffuser
• Passover
• Wick
• HME

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Bubble Humidifier
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Passover Humidifier
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Wick Humidifier(Concha-Pak)
GAS
heater
wick
H2O
H2O
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RCI Concha Pak
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Fisher-Paykel MR 390
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Wick Humidifier (Fisher-Paykel)
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Vapotherm 2000i

• Heated humidifier
• Wick-like (hollow gas filled fibers surrounded by
  heated water)
• Humidifies flow rates up to 40 LPM via nasal
  cannula or 20 LPM via trans-tracheal cannula
• Flows 5 40 LPM adult and 1 8 LPM neonatal
• 33-43o C output temperature

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• Vapor transfer cartridge
• Hundreds of hollow fibers filled with gas
  surrounded by heated water
• Voluntary Recall in 2005 FDA recall 2006.
  Ralstonia species of bacteria.  Ralstonia, as
  with any gram negative organism, may cause
  infection, sepsis and in most severe cases be
  life threatening.

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HME - Heat Moisture Exchangers

• Use when upper airway by-passed
• Made of material that traps patients own heat
  and moisture from an exhaled breath. (50
  efficient)
• Also called Artificial Noses
• HCH - Hygroscopic Condenser Humidifiers -
  superior to sponge-like material of HMEs. (70
  efficient)

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HMEs or HMEFs (HME Filters

• Not for patients with
• thick or bloody secretions
• core temperatures lt 32 o C
• Expired VT lt 75 of inspired VT
• VE gt 10 L/min

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Thermax HC Humidifier (HCH)

• The Thermax HCH combines chemically reactive
  Sodasorb and a conventional HME/HCH.
• The exothermic chemical reaction of converting
  expired carbon dioxide to calcium carbonate and
  water actively heats and provides moisture
• Exhaled carbon dioxide reacts with the Sodasorb
  to produce heat and moisture.
• Unlike a conventional, passive HME/HCH, inhaled
  moisture content and temperature are higher than
  exhaled moisture and temperature.
• One possible benefit of this active HME/HCH
  device is in hypothermic patients, in whom warm,
  humidified inhaled gases can help raise reduced
  body temperature.
• 79 mL deadspace compared to 10 mL from Gibeck

Broach, SD CG Durbin. A randomized, controlled,
clinical trial of a chemically-reactive heated
humidifier. RC. 2001 46 (1), 37-42.
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Inside Thermax HCH
http//www.enternetmedical.com/prod04.htm
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Thermax Hygroscopic Condenser
Sodasorb
sponge
http//www.enternetmedical.com/Anesthermax.jpg
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Summary

• Unheated humidifiers
• Make gas therapy more comfortable
• Bubble humidifiers
• Heated humidifiers
• Prevent humidity deficit
• Passover and wick humidifiers
• HME/HCH/heated HCH