Title: Humidity Therapy and Humidifiers
1Humidity Therapy and Humidifiers
- RET 2274
- Respiratory Care Theory 1
- Module 5.0
2Humidity Therapy and Humidifiers
- Humidity
- 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
3Humidity Therapy and Humidifiers
- Humidity Therapy
- 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
4Humidity Therapy and Humidifiers
- Humidity Therapy
- 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
5Humidity 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
6Humidity Therapy and Humidifiers
- Relative Humidity (RH)
- Is the ratio of actual content or weight or the
water present in a gas relative to the samples
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 gass capacity,
the RH is 100 - described as saturated
7Humidity 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
8Humidity Therapy and Humidifiers
- Relative Humidity (RH)
- ?Temp ?RH
- ?Temp ?RH
9Humidity 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
10Condensation
11Humidity 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
12Humidity Therapy and Humidifiers
- Humidity
- 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
13Humidity Therapy and Humidifiers
- Humidity
- 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
14Humidity Therapy and Humidifiers
- Humidity
- Partial Pressure
- Alveolar Air Equation
- FiO2 (PB Water Vapor Pressure) PaCO2
- 0.8
- .40 (760mm Hg 47 mm Hg) 40 mm Hg
- 0.8
15Humidity 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
16Humidity 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
17Humidity Therapy and Humidifiers
- Indications for Humidification
- Primary goal of humidification is to maintain
normal physiological conditions in the lower
airways or treat abnormal conditions
18Humidity 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
19Humidity 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
20Humidity 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
21Humidity Therapy and Humidifiers
- Equipment
- Humidifier is a device that adds molecular water
to gas
22Humidity 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
23Humidity 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
24Humidity Therapy and Humidifiers
- Physical Principles Governing Humidifiers
- Surface Area
- Bubble-diffuser type humidifiers
25Humidity Therapy and Humidifiers
- Physical Principles Governing Humidifiers
- Surface Area
- Wick technologies use porous water-absorbent
materials to increase surface area
26Humidity 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
27Humidity 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
28Humidity 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
29Humidity Therapy and Humidifiers
- Types of Humidifiers
- Passover Humidifier (Active)
- Directs gas over a water surface
- Two types
- Wick
- Membrane
30Humidity 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
31Humidity 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
32Humidity 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
patients exhalation and returns it to the
patient during the next inspiration
33Humidity Therapy and Humidifiers
- Types of Humidifiers
- HME (Passive)
- Best Suited for
- Short-term mechanical ventilation ( 96 hours)
- Minute ventilation lt 10 L/min
- Limited secretions
- Normal body temperature
34Humidity 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.
35Humidity 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
36Humidity Therapy and Humidifiers
- Heaters, Reservoir, and Feed Systems
37Humidity Therapy and Humidifiers
- Heaters, Reservoir, and Feed Systems
38Humidity Therapy and Humidifiers
- Heaters, Reservoir, and Feed Systems