Humidity Flashcards
Humidity therapy
It involves adding water vapour and heat to the inspired gas
Humidifier -device
Principle
temperature
The higher the temperature the more water vapour it can hold
Surface area
Greater the contact between water and gas the more opurtunitynfor evaporation to occur
Contact time
The longer the gas remains in contact with water greater opurtunity to evaporate
Thermal mass
Greater the mass of water or core element of a humidifier the greater the capacity to hold and transfer heat
Types
Active humidifier
Actively adding heat or water or both to the device patient interface
Eg
Passover humidifier
Bubble humidifier
Nebulizer
Passive humidifier
Recycling exhaled heat of humidity from the patient
Eg heat and moisture exchange
Passover humidifier
It directs gas over a surface containing water
3 common types
Simple reservoir type
Gas flows over the surface of the volume of water
The surface for gas fluid interface is limited typicaly used with heated fluids
Wick type
- uses an absorbent material (Wick to increase the surface area for dry air to interface with heated valve
- wick is placed upright with gravity dependent end in water reservoir surrounded by a heating element
-capillary action continuoslybdraws water to keep the wick saturated
Dry air
↓
Flows around the wick
↓
Leaves the chamber fully saturated with water vapour
____________________
Membaraneous type
- uses a hydrophobic membarane
- water is saperated from gas stream by hydrophobic membarane
- membarane permit water vapour to pass through but not liquid water
Note-wick and membarane type don’t produce aerosol
Bubble humidifier
★direct gas through a tube or channel into the bottom of a water reservoir, where gas stream products bubbles that rise through the device outlet to the patient
★the gas within the bubbles is humidified as the bubbles rise to water surface
★ increase in height of water column increases the humidity content if the bubbles
★limitingbthere effectiveness at flow rates greater than 10L/m
★ at high flow rates bubble humidifier produce aerosol
Nebulizer
★humidity is simply h2o in the gas phase whereas bland aerosol consist of liquid particles suspended in a gas
★delivers sterile water or hypotonic isotonic or hypertonic saline aerosols
★use large volume jet nebulizer and ultrasonic nebulizer to generate aerosols
Heat and moisture exchanger
★also called artificial nose
★captures exhaled heat and moisture and uses it to heat and humidity therapy next inspiration
★ can be used to provide humidifier for mechanically ventilated patient
★ provides about 70% of exhaled heat and moisture to next breath
★3 types-simple condenser humidifier
Hygroscopic condenser humidifier
Hydrophobic condenser humidifiers
★contraindications
-increased vomulme of secretion
- thick dehydrated secretions
- hypothermia
- uncuffed etts
- when pt is under aerosol therapy
- can’t be used with heated humidifiers
Simple condenser humidifier
★contains a condenser element with a high thermal conductivity
★50%efficiency
On inspiration,inspired air cools the condenser element
↓
On exhalation,expired watervapour condenses directly on its surface and rewarms it
↓
On next inspiration,cool dry air is warmed and humidifies ad it passes over the condenser element
Hygroscopic condenser humidifier
★uses a condenser element of low thermal conductivity (paper ,wool) impregnating with hygroscopic salt which help to retain more heat thn simple hme
★hygroscopic salt (helps to capture extra moisture from exhaled air )
During exhalation some water vapour condenses on cool condenser element,wher as other water molecule bind directly to the hygroscopic salt
↓
During inhalation,the lower water vapour pressure in the inspired gas liberates water molecule directly from the hygroscopic salt without cooling
Hydrophobic condenser humidifier
★uses water repellant element with a large surface area of low thermal conductivity
★70%efficiency
During exhalation,the condenser temperature increases to approx 25°c
↓
On inhalation,cool gas and evaporation cools the condenser down to 10°c
This large temperature change results in the conservation of more water to be used in humidifying the next breath
