Humidifiers (Humidity Therapy)

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It is adding up of water-vapor and heat to the inspired gas.

Physiology
The primary functions of the upper respiratory tract is heat and moisture exchange and filtration.
The nasal mucosal lining is kept moist by the secretion from mucous glands.
The high vascularity of the mucosa provides heat transfer.
The nasal mucosa is cooled during inhalation and heated during exhalation.
cooled air holds less water vapor and vice versa.


Isothermic Saturation Boundary:
It is the boundary above which temperature and humidity decreases during inspiration and increases during exhalation.
Normally this boundary is 5cm below the carina.
ISB will shift down in cases of:
Breathing cold air, breathing dry air, and bypassed airways etc...

Breathing indications:
To humidify dry medical gases, when upper airways are bypassed.

Secondary
To manage hypothermia in intra-operative.
To treat bronchospasm created by cold air especially after exercise.
If the application of dry medical gas is prolonged there will be structural damage of upper respiratory tract.
Ciliary motility decreases
Airways become irritable
Increased mucous production
Thickening of mucosa
Airway epithelial destruction
leading to Atelectasis.

In cases of endotracheal incubation the heat and moisture exchange capability is lost and hance the danger is high.

Equipments:

Humidifiers:
Is the device that adds molecular water and heat to gas.

Principles of Humidifiers

Temperature
Surface Area
Time of contact

Temperature:
Greater the temperature greater the water vapor it can hold.  So heated humidifier out performs. Normal temp. 40 degree C.

Surface Area
Greater the area of contact, greater the humidification.

Time of Contact
Greater the contact time, greater the evaporation.

Types of Humidifiers
3 primary types of humidifiers
   Bubble
   Pass over (wick type, membrane type)
  Heat and moisture exchange (artificial nose)
      Simple condenser humidifier
      Hygroscopic condenser humidifier
      Hydrophobic condenser humidifier
It can be classified as heated and non heated humidifier

Bubble Humidifier
Breaks an under water gas stream into small bubbles













Pass over
  Wick humidifiers
It is a cylinder of absorbant material.  The wick will absorb water from reservoir and heat itself moistened.
The dry gas passes over this and takes up the moisture.

   Membrane Humidifier
In this a hydrophobic membrane separates water from gas stream through which water molecule can pass but not liquid water.
Heat and moisture exchange (artificial nose)
It is mainly used with endo tracheal and tracheostomy tubes.
Simple condensor humidifiers
It contains an element with high thermal conductivity like in metalic gauze, parallel metal tubes etc...
Hygroscopic condenser humidifier
Uses an element of low thermal conductivity like paper, wool, foam etc..
This element is impregnated with hygroscopic salts like Ca++ or lithium chlorides.
This salt helps to capture the extra moisture
Efficiency 70%.

Hydrophobic Condenser Humidifiers:
It uses water repellent element with large surface area and low thermal conductivity.
Some provide bacterial filtration efficiency 70%.
Contraindication:
Thick copious and bloody secretions.
Patients with high spontaneous minute volume.
Body temp <32 C.