Egan's Chapter 39: humidity and bland aerosol therapy
Prolonged breathing of improperly conditioned gases through a tracheal airway can result in
- Hypothermia - inspissation of airways secretions - mucociliary dysfunction - destruction of airway epithelium - atelectasis
Some hydrophobic HME that provide bacterial filtration may reduce the risk for an ammonia but be unsuitable for patients with
- Limited respiratory reserve - Those prone to airway blockage because they may increase artificial airway occlusion
As the airway is exposed to relatively cold dry air:
- Ciliary motility is reduced - Airways become more irritable - mucus production increases - pulmonary secretions become inspissated (thickened and dried, owing to dehydration)
For bubble humidifiers, contact time depends on the
- Depth of the water column - the deeper the column, the greater time of contact as the bubbles rise to the surface
Hazards and Complications for humidification therapy (Box 39.2 p 819)
- Hazards and complications associated with the use of HH & HME units during mechanical ventilation include the following: Potential electric shock Potential for burns to caregivers from hot metal (hypothermia, hyperthermia, thermal injury) - Under hydration and mucus impaction (HME unit or HH): -Hypoventilation and/or alveolar gas trapping, resulting from mucus plugging of airways -hypoventilation secondary to hypercapnia caused by the increase in dead space -increased work of breathing -possible hypoventilation resulting from hypercapnia caused by the increase in dead space - -inadvertent overfilling or pulled condensate, resulting in unintentional tracheal lavage -high flow rates during disconnect, which can aerosolize contaminated condensate -elevated airway pressure is caused by condensation -ineffective low pressure alarm during disconnection -patient-ventilator dysnchrony and improper ventilator function caused by condensation in the circuit -airway burns or tubing melt down if heated wire circuits are covered or in compatible with the humidifier
Humidifiers are either
1. Active (actively adding heat, water, or both to the device patient interface) 2. passive (recycling exhaled heat and humidity from the patient)
Active humidifiers include (4)
1. Bubble humidifiers 2. passover humidifiers 3. nebulizers of blend aerosols and 4. vaporizers
Hygroscopic condenser HME unit use materials that
1. Incorporate a condensing element of low thermal conductivity 2. Impregnate this material with a hygroscopic salt
A reduction of __ mg/l below BTPS (44 mg/l) is less than __% RH at BTPS (p 819)
20 mg/l; 60%
What is the recommended temperature range for the nose/mouth
20-22
During exhalation, the condenser temperature increases to approximately __°C because of conduction and the latent heat of condensation
25 °C
What is the recommended temperature range for the hypopharynx
29-32
As gas expansion and evaporation cold water and I'm here at humidifiers to __°C below ambient temperature, the humidifiers become less efficient
30
HME unit that deliver at least __ mg H2O/L should be used because they are associated with a lower incidence of ETT occlusion
30
What is the recommended temperature range for the trachea/carina
32-35
RULE OF THUMB (p 819) Despite minimal levels in the standards, delivery of inspired gas to the lower airways at __C or even 34C with 100% RH may not be sufficient to prevent the occupancy of epithelial damage during a 6 hour exposure
33 C
What is the recommended temperature range for the lungs (ISB)
37
When a person inhales through the mouth at normal room temperature, pharyngal temperatures are approximately __°C less than when the person breathes through the nose with __% less RH
3: 20%
Normally approximately __ cm below the carina, is called the
5 cm; isotherm is saturation boundary (ISB)
RULE OF THUMB (p 823) As many as __% of HME units do not provide the recommended inspired AH of 30 mg H2O/l. Check manufacturing performance specifications and independent bench studies before adopting an HME unit for clinical use
50%
What is the recommended relative humidity % range for the nose/mouth
50%
Inspired air cools the condenser element, an expired water vapor condenses directly on its surface and rewarms it. On the next inspiration, cool dry air is warm and humidified as it passes over the condenser element. Simple condenser humidifiers can recapture only some __% of a patient's exhaled moisture - how much is returned?
50%; 20 mg/l
As long as the inspired humidity is at least __% of BTPS conditions, no injury occurs in normal lungs
60
Similar to the nose, the HME captures exhaled heat and moisture and returns up __% of the heat and humidity to the patient during the next inspiration
70%
The efficiency of hydrophobic condenser units is comparable to that of Hygroscopic condenser HMEs (approximately __%)
70%
The ideal HME unit should operate at __% efficiency or better
70%
Hygroscopic typically achieve approximately __% efficiency (how much is exhaled and returned)
70%; 40 mg/l exhaled and 27 mg/l returned
What is the recommended relative humidity % range for the hypopharynx
95%
Administration of dry medical gases at flows greater than __l/min to the upper airway causes immediate heat and water loss and, if prolonged, causes ??
>4 l/min; structural damage to the epithelium
Similarly, the mucosa lining this sinuses, trachea, and bronchi aid in __ & __ inspired gases
Heating and humidifying
Is the process which occurs by evaporation of water from a surface to a gas that is not 100% saturated with water vapor whether the water is in a reservoir, a wick, or sphere of water in suspension (aerosol)
Humidification
Device that adds molecular water to gas
Humidifier
Involves adding water vapor and (sometimes) heat to the inspired gas
Humidity
Which HME unit uses a water repellent element with a large surface area and low thermal conductivity
Hydrophobic condenser
Which HME unit uses materials that absorb moisture in the air
Hygroscopic
The primary stimulus is probably a combination of airway cooling and drain which leads to the
Hypertonicity of airway lining fluid in the release of chemical mediators
This recruitment of airways that do not typically provide this level of heat and humidity can have a __ impact on epithelial integrity
Negative
Hydrophobic ("water hating") membranes have a little or no tendency to absorb water and Typically have a
Nonpolar surface that repels water (p 822)
Unheeded bubble humidifiers are commonly used with
Oxygen delivery systems to raise the water vapor content of the gas to ambient levels
__ Humidifiers pass gas over a large surface area of water
Pass over
__ humidifiers direct gas over a surface containing water
Pass over
Although invisible to the naked eye, these water droplet suspensions can transmit ___ from the humidifier Reservoir to the patient
Pathogenic bacteria (contamination)
Which humidifier contain a condenser element with high thermal conductivity; the latter usually consist of metallic gauze, corrugated metal, or parallel metal tubes.
Simple condenser units
To warn of pat float obstruction and prevent bursting of humidifier bottle, bubble humidifiers incorporate a
Simple pressure relief valve or pop-off
Which device directs gas over the surface of a volume of water or fluid. The surface for gas-fluid interface is limited.
Simple reservoir device
Which device is typically used with heated fluids during invasive mechanical ventilation, room temperature fluids may be used with noninvasive ventilator support (nasal CPAP or bilevel ventilation)
Simple reservoir device
What has been used in ambulatory settings for years as a room humidifiers
Simple room vaporizers
What humidifier heats water to the point of expansion as a gas
Simple vaporizers
Because any device that generates an aerosol poses a high risk for spreading infection, ____must be followed when these systems are used
Strict infection control procedures
The greater the area of contact between water and gas, the more opportunity there is for evaporation to occur is called?
Surface tension
Humidity is water in its gaseous or molecular form and its quantity depends on the __ of the gas
Temperature
Is an important factor affecting humidifier performance
Temperature
__ The greater the amount of water in a humidifier the greater the
Thermal mass
True or false: Increased thermal mass equates to increased capacity to hold and transfer heat to therapeutic gases
True
True or false: The higher the temperature of a gas, the more water vapor it can hold
True
The delivery of Call humidifier gas is used to treat * this technique is used most often in conjunction with bland aerosol delivery
Upper airway inflammation resulting from croup, epiglottitis, and postextubation edema
Traditionally, HME units have been mainly used to provide humidification to patients receiving
Ventilatory support via endotracheal or tracheostomy tubes
The incident of cold air intake is bronchospasm can be reduced by
Wearing a scarf over the nose and mouth and cold weather (the scarf becomes a crude passes HME device)
AH
absolute humidity
The mouth is less effective at HGM then the nose because of ??
- The low ratio of gas volume to moist and warm surface area and - the less vascular squamous epithelium lining the oropharnx and hypopharnx
The ideal HME unit should operate at 70% efficiency or better, providing
- at least 30 mg/l water vapor - Use standard connections - have a low compliance - add minimal weight, dead space, & flow resistance to breathing circuit
What are the 2 primary indications of humidification therapy (Box 39.1, p 819)
- humidifying dry medical gases - overcoming humidity deficit created when the upper airway is bypassed
That nasal mucosal lining is kept moist by
- secretions from mucous glands - goblet cells - transudation of fluid through cell walls - condensation of exhaled humidity
Numerous factors can shift the ISB deeper into the lungs. The ISB shifts distally when a person breathes through the mouth rather than the nose:
- when the person breathes cold dry air - when the upper airway is bypassed (breathing through artificial tracheal airway) - when the minute ventilation is higher than normal
What are the clinical signs and symptoms of INADEQUATE AIRWAY HUMIDIFICATION *not on enough/or hot humidity
-atelectasis -dry, non productive cough -increased airway resistance -increased incidence of infection -increased work of breathing -Patient complaint of substernal pain and airway dryness -Thick. dehydrated secretions
Compared with bubble humidifiers, Pass over, wick, and membrane humidifiers offer several advantages (3)
1. Maintain heat and saturation at higher flow rates than bubbling or jet humidifiers 2. Add a little or no flow resistance to spontaneous breathing circuits 3. Do not generate any aerosol impose minimal risk for spreading infection
What are the three common types of Pass over humidifiers
1. Simple Reservoir type 2. Wick type 3. Membrane type
Three basic types of HME units are
1. Simple condenser humidifiers 2. Hygroscopic condenser humidifiers 3. Hydrophobic condenser humidifiers
The following four variables or principles affect the performance of a humidifier. These factors are exploited to various degrees in the design of humidification devices (box 39.4)
1. Temperature 2. surface area 3. time of contact 4. thermal mass
Physical principles governing humidifier function (box 39.4, p 820)
1. temperature - The higher the temperature of a gas, the more water vapor it can hold (increased capacity), and vice versa 2. surface area - The greater the surface area of contact between water and gas, the more opportunity for evaporation to occur 3. contact time - The longer a gas remains in contact with water, the greater the opportunity for evaporation to occur 4. thermal mass - The greater the mass of water or the core element of a humidifier, the greater its capacity to hold and transfer heat
What are the 8 secondary indications of humidification therapy (Box 39.1, p 819)
1. treating bronchospasm caused by cold air 2. With thick, copious, or bloody secretions 3. With an expired tidal volume (VT) less than 70% of the delivered VT (pt's when large bronchopleural fistula or incompentent or absent endotracheal tube cuffs) 4. with a body temp below 32C 5. with high spontaneous minute volumes (>10 l/min) 6. receiving noninvasive ventilation with large mask leaks, by the pt does not exhaleenought VT to replenish heat and moisture to adequately condition the inspired gas. Also, the resistance and dead space of the HME may negate the effects of the noninvasive positive pressure and add additional work of breathing 7. receiving lung-protective ventilation strategies, as in acute respiratory distress syndrome (the additional dead space of HME may increase the ventilation requirement and PcCO2) 8. Receiving in-line aerosol drug treatments (a standard HME must be removed from the pt circuit during treatments. An HME designed for aerosol delivery must be switched to the aerosol bypass mode.)
As gas flow increases, the Reservoir calls and contacts time is reduced, limiting effectiveness at flow rate greater than
10 l/min
At room temperature, __ mg/l AH corresponds to approximately __% RH but only approximately __% body humidity
10 mg/l; 80%; 25%
What is the recommended relative humidity % range for the lungs (ISB)
100%
What is the recommended relative humidity % range for the trachea/carina
100%
On inspiration, cool gas and evaporation reduces the condenser temperature down to __ °C. This large temperature change results in the conversation of more water to be used in humidifying the next breath
10°C
Unheated bubble humidifiers can provide AH levels between approximately
15 and 20 mg/l
In contrast to the nose, with its reach vasculature and endothelium, most HME units do not actively add
Heat or water to the system
The nasal mucosa is very vascular; actively regulating temperature changes in the nose and serving as an active element in promoting effective ??
Heat transfer
What kind of units typically comprise a passive humidifier, also described as an "artificial nose"
Heat and moisture exchange (HME)
Passive humidifiers are typical
Heat and moisture exchangers
Humidity therapy is also used to treat ? (p 818)
Abnormal conditions
Humidity is expressed as __ humidity & __ humidity
Absolute & relative
__ is measured by weighing the water vapor extracted from the air, using a dry agent
Absolute humidity (AH)
As gas flow increases, bubble humidifiers can produce
Aerosols
RULE OF THUMB (p 822) J., Bubblz, and ultrasonic humidifiers produce __ that can carry bacteria from the reservoir to the patient. Minimize contamination of the reservoir by draining condensate away from the humidifier, and rinse, wash, sterilized, or replace frequently
Aerosols
Warming and humidifying the inspired gas can help to
Alleviate bronchospasm in patients who develop airway narrowing after exercise OR when they breathe cold air
Specifications covering the design and performance requirements for medical humidifiers are established by the
American society for testing and materials (ASTM)
The pop off can be used to test
And O2 delivery system for leaks but obstructing delivery tubing at or near the patient interface
Which device separate heated water from the gas drain by means of hydrophobic membrane.
Membrane type humidifiers
Humidifier pop off should provide both an __ and a __ alarm and resume normal position when pressure returns to normal
Audible and visible
As inspired gas moves into the lungs, it achieves
Body, temperature, and pressure saturated (BTPS) conditions (i.e. body temperature, 37C; barometric pressure; saturated with water vapor [100% RH at 37C]
__ Direct stream of gas under water, where it is broken up into small bubbles as the gas bubbles rise to the surface, evaporation increases the water vapor content within the bubble the smaller. the bubble, the greater the ratio of water to air at the surface area
Bubble diffusion
More space efficient ways to increase the ratio of water to gas surface area include
Bubble diffusion, aerosol, and wick technologies
What kind of humidifier breaks or diffuses in underwater guestroom into small bubbles
Bubble humidifier
During exhalation, the RH of expired gas varies little between mouth breathing and nose breathing, but the mouth is much less efficient in reclaiming __ & __
Heat and water
A __ __ __ Is a thin film, high surface area boiler that combines capillary force in phase transition to import pressure onto an expanding gas (water vapor) and ejects it into the gas stream
Capillary force vaporizer
What should you do when there reports of an increase incident of blocked tracheal tube associated with the long-term use of HME deices in the ICU are in contrast to evidence supporting their long-term views in spontaneously breathing patient
Change as needed
Insufficient key and humidification can occur with some HME units causing
Complications
Below the ISB, temperature and RH remain __
Constant BTPS
The longer a gas remains in contact with water, the greater opportunity for evaporation to occur.
Contact time
The lower water vapor pressure in the inspired gas liberate water molecules directly from the hygroscopic salt without
Cooling
Heating the reservoirs can increase humidity content, but this is not recommended because
Cooling produces a condensate that obstructs small-bore delivery tubing
Breathing dry gas through an ETT can cause
Damage to the tracheal epithelium within minutes
HME long-term needs with laryngectomies show a significant __ in the frequency of coughing, forced Expectoration, and stoma cleaning were reported with a __ in pulmonary symptoms and improvement of sleep and speech regardless of country or climate
Decrease
Above the ISB, temperature and humidity __ during INSPIRATION and __ during EXPIRATION
Decrease; Increase
Proper levels of heat and humidity help to
Ensure normal function of the mucociliary transport system
Delivery of inspired gas at 30C or even 34C with 100% RH may not be sufficient to prevent
Epithelial damage occurring during a 6-hour exposure
Aerosols suspended in a gas stream have
Extended contact time (and opportunity for evaporation) as the aerosol and gas travel to the patient
The amount of heat and humidity that a patient needs depends on the site of
Gas delivery (nose, mouth, hypopharynx, trachea)
Large reservoir humidifiers can produce more consistent heat and humidification with a broader range of
Gas flow
__ is a primary function of the upper respiratory tract, mainly the nose
HME
These shifts of the ISB can compromise the body's normal __, in which case humidity therapy is indicated
HME mechanisma
By using an element with low thermal conductivity, hygroscopic condenser HME units can retain more __ than simple condenser systems, while hygroscopic salt helps capture extra moisture from the exhaled gas
Heat
The nose heats humidifies gas on __; it cold the gas and reclaims water the gas that is __
Inspiration; exhaled
ISO
International Organization for Standardization
Design and performance standards for HME units are set by the
International Organization for Standardization (ISO)
In passover and wicked type humidifiers the flow rate of gas through the humidifier is
Inversely related to contact time, with high flow rates reducing the time available for evaporation to occur
ISO
Isothermic saturation boundary
AH, the amount fo water in a given volume of gas, is usually expressed in ??
Milligrams per liter (mg/L)
If the pop off sounds, the system is leak free; failure of the pop off to sound may indicate a
Leak or a faulty pop off valve
Box 39.2 - the hazard of breathing dry gas is even greater when the normal heat-and-water-exchange capabilities of the upper airway are __ or __, as occurs with endotracheal intubation
Lost or bypassed
RULE OF THUMB: The heat and humidity (AH) of a medical gas should be targeted to __ conditions found in normal airways at the part of the airway where the gas is being introduced
Match
RH, the amount of water vapor in a volume of gas, is expressed as a __ of the amount of water vapor required to fully saturate that gas at the same temperature and pressure
Percentage
The __ Is commonly a gravity or a spring-loaded valve that releases pressure is greater than 2 psi
Pop off
Water vapor (molecules) pass through the __ in the membrane, but liquid water and pathogens cannot *no bubbling
Pores
Warmed, humidifier gases are used to
Prevent or treat various abnormal conditions
In the treatment of hypothermia, heating and humidifying the inspired guess is one of the several techniques used to
Raise core temperatures back to normal
When this shift of ISB occurs, additional surfaced of the airway are
Recruited to meet the heat and humidity requirements of the lung
Heated humidification is used to
Reduce intraoperative hypothermia
No bubbling occurs, so no aerosol is produced - which pass over device is this?
Wick humidifier
Which device is typically placed upright with the gravity dependent and in a heated water reservoir. Heating elements might be below or surrounding the device. Capillary action draws water from the reservoir and keeps it saturated. As dry gas enters the chamber, it flows around the __, quickly picking up heat and moisture and leaving the chamber saturated with water vapor.
Wick humidifier
Which device uses an absorbent material to increase the surface area for dryer to interface with heated water
Wick humidifier
__ use porous water absorbent materials to draw water similar to a sponge into its fine honeycomb destruction by means of capillary action. The surfaces of the __increase the area of contact between the water and gas, which is evaporation
Wicks
The primary goal of humidification is to
maintain normal physiologic conditions in the lower airways
RH
relative humidity
