1. Humidity Therapy and Humidifiers
RET 2274
Respiratory Care Theory 1
Module 5.0

2. Humidity Therapy and Humidifiers
Water that exists as individual molecules in the vaporous or gaseous state and is present in the air we breathe – often described as water vapor

3. Humidity Therapy and Humidifiers
Involves adding water vapor and (sometimes) heat to an inspired gas
Primary goal of humidification is to maintain normal physiological conditions in the lower airways or treat abnormal conditions

4. Humidity Therapy and Humidifiers
Administration of dry medical gases at flows greater than 4 L/min to the upper airway causes immediate heat and water loss, and if prolonged, causes structural damage

5. Humidity Therapy and Humidifiers
Absolute Humidity
Is the actual content or weight of water present in a given volume of gas
Expressed as:
Grams per cubic meter (g/m3)
Milligrams per liter (mg/L)
Also know as water content

6. Humidity Therapy and Humidifiers
Relative Humidity (RH)
Is the ratio of actual content or weight or the water present in a gas relative to the sample’s capacity to hold water at that temperature
Expressed as a percentage
RH = measured humidity (content) X 100
water capacity
When the amount of water that a gas contains at a given temperature is equal to the gas’s capacity, the RH is 100% - described as saturated

7. Humidity Therapy and Humidifiers
Relative Humidity (RH)
Increasing the temperature of a gas, increases its capacity to hold water
If absolute humidity is held constant, increasing the temperature of the gas will decrease the RH
If absolute humidity is held constant, decreasing the temperature of the gas will increase the RH or it will remain at 100%

8. Humidity Therapy and Humidifiers
Relative Humidity (RH)
Temp RH
Temp RH

9. Humidity Therapy and Humidifiers
Condensation
Cooling a gas that has an RH of 100% decreases its capacity to hold water, which results in water being squeezed out of the gas
Temp RH

10. Condensation

11. Humidity Therapy and Humidifiers
Evaporation
The process of water moving from a liquid to a gaseous state at temperatures lower than its boiling point
The warmer the air contacting the water surface, the faster the rate of evaporation
Heating water will increase the rate of evaporation

12. Humidity Therapy and Humidifiers
Partial Pressure
The random motion of water molecules exerts a pressure (water vapor pressure) in a way similar to gas exerting pressure
As the temperature of a gas increases, kinetic activity increases, so the pressure also increases

13. Humidity Therapy and Humidifiers
Partial Pressure
Its magnitude is solely dependent upon temperature and relative humidity – not upon barometric pressure
The partial pressure of water vapor must always be accounted for (subtracted) when calculating the partial pressure of other gases in a mixture

14. Humidity Therapy and Humidifiers
Partial Pressure
Alveolar Air Equation
[FiO2 (PB – Water Vapor Pressure)] – PaCO2
0.8
[.40 (760mm Hg – 47 mm Hg)] – 40 mm Hg

15. Humidity Therapy and Humidifiers
Physiological Control of Heat and Moisture Exchange
Primary function of the upper respiratory tract
Nose (primary)
Heats and humidifies gas on inspiration and cools and reclaims water from the gas that is exhaled
Sinuses, Trachea, and Bronchi
Also aid in heating and humidifying the inspired gases

16. Humidity Therapy and Humidifiers
Physiological Control of Heat & Moisture Exchange
As inspired gas moves into the lungs, it achieves BTPS (body temperature, 37 C; barometric pressure; saturated with water vapor [100% relative humidity at 37 C])
Isothermic Saturation Boundary (ISB)
The point in the respiratory tract at which incoming gas reaches BTPS
Below the ISB, temperature and relative humidity remain the same

17. Humidity Therapy and Humidifiers
Indications for Humidification
Primary goal of humidification is to maintain normal physiological conditions in the lower airways or treat abnormal conditions

18. Humidity Therapy and Humidifiers
Indications for Humidification
Administration of dry medical gases at flows greater than 4 L/min to the upper airway causes immediate heat and water loss, and if prolonged, causes structural damage
Ciliary motility is reduced
Airways become irritable
Mucous production increases
Pulmonary secretions become thick and inspissated

19. Humidity Therapy and Humidifiers
Indications for Humidification
Prolonged breathing of improperly conditioned gases through a tracheal airway can result in the following:
Hypothermia
Inspissation of airway secretions
Mucociliary dysfunction
Destruction of airway epithelium
Atelectasis
As long as inspired humidity is at least 60% of BTPS conditions, no injury occurs in normal lungs

20. Humidity Therapy and Humidifiers
Indications for Humidification
Humidified gas delivered to an artificial airway (endotracheal or tracheostomy tube) must be between 31 and 35 C with a minimum of 30 mg/L of absolute humidity
To maintain the appropriate temperature and humidity levels, monitoring at the interface of the patient and humidifying device is necessary

21. Humidity Therapy and Humidifiers
Equipment
Humidifier is a device that adds molecular water to gas

22. Humidity Therapy and Humidifiers
Physical Principles Governing Humidifiers
Temperature
The greater the temperature of a gas, the more water it can hold
The cooler the water in a humidifier the less efficient they are

23. Humidity Therapy and Humidifiers
Physical Principles Governing Humidifiers
Surface Area
The greater the area of contact between water and gas, the more opportunity for evaporation to occur
Passover humidifiers pass gas over a large surface area of water

24. Humidity Therapy and Humidifiers
Physical Principles Governing Humidifiers
Surface Area
Bubble-diffuser type humidifiers

25. Humidity Therapy and Humidifiers
Physical Principles Governing Humidifiers
Surface Area
Wick technologies use porous water-absorbent materials to increase surface area

26. Humidity Therapy and Humidifiers
Physical Principles Governing Humidifiers
Contact Time
The longer gas remains in contact with water, the greater the opportunity for evaporation to occur
Depth of water column (bubble type)
 depth of water  evaporation
 depth of water  evaporation
Flow rate of gas (passover and wick)
 flow rate  evaporation
 flow rate  evaporation

27. Humidity Therapy and Humidifiers
Types of Humidifiers
Active
Actively adds heat and/or water to the device/patient interface
Bubble
Passover
Membrane
Passive
Recycling exhaled heat and humidity from the patient
HME

28. Humidity Therapy and Humidifiers
Types of Humidifiers
Bubble Humidifier (Active)
Breaks an underwater gas stream into small bubbles
Unheated – commonly used oronasal O2 delivery systems (e.g., cannula)
Goal; to raise the water vapor content of the gas to ambient levels
Can generate aerosols at high flows
Equipped with pressure-relief valve “pop-off”

29. Humidity Therapy and Humidifiers
Types of Humidifiers
Passover Humidifier (Active)
Directs gas over a water surface
Two types
Wick
Membrane

30. Humidity Therapy and Humidifiers
Types of Humidifiers
Passover Humidifier
Wick type
A cylinder of absorbent material (wick) is placed upright in a reservoir of water and surrounded by a heating element
Dry gas enters the chamber, flows around the wick, picks up moisture, and leaves the chamber saturated with water vapor

31. Humidity Therapy and Humidifiers
Types of Humidifiers
Passover Humidifier
Membrane type
Separates the water from the gas stream by means of a hydrophobic membrane
Water vapor molecules pass through the membrane (liquid cannot)
Dry gas enters the chamber, flows across the membrane, picks up moisture, and leaves the chamber saturated with water vapor

32. Humidity Therapy and Humidifiers
Types of Humidifiers
Heat and Moisture Exchangers (HME)
Passive humidifier
Functions similar to the upper airway
Captures exhaled heat and moisture during a patient’s exhalation and returns it to the patient during the next inspiration

33. Humidity Therapy and Humidifiers
Types of Humidifiers
HME (Passive)
Best Suited for:
Short-term mechanical ventilation (≤ 96 hours)
Minute ventilation < 10 L/min
Limited secretions
Normal body temperature

34. Humidity Therapy and Humidifiers
Types of Humidifiers
HME (Passive)
Rule of Thumb
You can estimate if an HME is performing well at the bedside by visually confirming condensation in the flex tube. Lack of condensate may be a clue that humidification is less than adequate and that alternative systems may be appropriate for use with that particular patient.

35. Humidity Therapy and Humidifiers
Heaters, Reservoirs, and Feed Systems
Heat improves the water output of bubble and passover humidifiers
Heated humidifiers are used mainly for patients with bypassed upper airways and/or for those receiving mechanical ventilatory support

36. Humidity Therapy and Humidifiers
Heaters, Reservoir, and Feed Systems

37. Humidity Therapy and Humidifiers
Heaters, Reservoir, and Feed Systems

38. Humidity Therapy and Humidifiers
Heaters, Reservoir, and Feed Systems