humidity therapy and humidifiers ret 2274 respiratory care theory 1 module 5.0
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Humidity Therapy and Humidifiers
RET 2274
Respiratory Care Theory 1
Module 5.0
Humidity 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
Humidity 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
Humidity 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
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
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
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%
Humidity Therapy and Humidifiers
Relative Humidity (RH)
Temp RH
Temp RH
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
Condensation
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
Humidity 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
Humidity 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
Humidity 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
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
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
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
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
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
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
Humidity Therapy and Humidifiers
Equipment Humidifier is a device that adds molecular
water to gas
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
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
Humidity Therapy and Humidifiers
Physical Principles Governing Humidifiers Surface Area
Bubble-diffuser type humidifiers
Humidity Therapy and Humidifiers
Physical Principles Governing Humidifiers Surface Area
Wick technologies use porous water-absorbent materials to increase surface area
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
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
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”
Humidity Therapy and Humidifiers
Types of Humidifiers Passover Humidifier (Active)
Directs gas over a water surface Two types
Wick Membrane
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
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
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
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
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.
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
Humidity Therapy and Humidifiers
Heaters, Reservoir, and Feed Systems
Humidity Therapy and Humidifiers
Heaters, Reservoir, and Feed Systems
Humidity Therapy and Humidifiers
Heaters, Reservoir, and Feed Systems