humidity therapy and humidifiers ret 2274 respiratory care theory 1 module 5.0

Humidity Therapy and Humidifiers

RET 2274

Respiratory Care Theory 1

Module 5.0


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 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 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


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


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


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%


Relative Humidity (RH)

Temp RH

Temp RH


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


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 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



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



Alveolar Air Equation

[FiO2 (PB – Water Vapor Pressure)] – PaCO2

0.8

[.40 (760mm Hg – 47 mm Hg)] – 40 mm Hg 0.8


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


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


Indications for Humidification Primary goal of humidification is to maintain

normal physiological conditions in the lower airways or treat abnormal conditions


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


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


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


Equipment Humidifier is a device that adds molecular

water to gas


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


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



Bubble-diffuser type humidifiers



Wick technologies use porous water-absorbent materials to increase surface area


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


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


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”


Types of Humidifiers Passover Humidifier (Active)

Directs gas over a water surface Two types

Wick Membrane


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


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


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


Types of Humidifiers HME (Passive)

Best Suited for: Short-term mechanical

ventilation (≤ 96 hours) Minute ventilation < 10 L/min Limited secretions Normal body temperature


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.


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


Heaters, Reservoir, and Feed Systems

humidity therapy and humidifiers ret 2274 respiratory care theory 1 module 5.0

Documents

humidifiers humidity

humidifiers absolute

water vapor slide

water content slide

water capacity

pressure water vapor

process of water

water loss