Chapter 39 Flashcards
Humidity Therapy
therapy that adds water vapor and sometimes heat to inspired gas
Humidity
water in its gaseous or vapor form in the environment (invisible)
Absolute Humidity (AH)
amount of water in a given volume of gas (mg/L)
Relative Humidity (RH)
ratio between the amount of water in given volume of gas and max amount it is capable of holding at same temperature and pressure
Formula for relative humidity
RH = absolute humidity capacity x 100
Aerosol
suspension of water particulate, a mist you can visibly see, in gases that can be inhaled (nebulizers)
Nose on inhalation
- warms air and picks up water vapor from moist mucosal lining
- filters inhaled gases
Nose on exhalation
- exhaled gases transfer back to cooler trachea holding less water vapor
- condensation occurs on mucosal surfaces
- liquid water is reabsorbed by mucus (rehydration)
What is BTPS
Body Temperature Pressure Saturated
___ relative humidity at 37 C
100%
Gas at body temperature and ambient pressure (BTPS) contains ____ mg/L of water vapor
43.9 mg/L
Above ISB
temperature and relative humidity decrease during inspiration and increase during exhalation
Below ISB
temperature and relative humidity remain constant
ISB shifts distally when
- person breathes cold, dry air
- airway is bypassed (tracheostomy)
- minute ventilation is higher than normal
Shifts of ISB
can compromise body’s normal heat and exchange mechanisms
What is ISB
isothermal saturation boundary
Nose and mouth
T = 22 C
RH = 50%
AH = 10 mg/L
Larynx/Pharnyx
T = 30 C
RH = 95%
AH = 30 mg/L
Lungs
T = 37 C
RH = 100%
AH = 43.9 mg/L
Humidity deficit:
43.9 mg/L - 10.0 mg/L = 33.9 mg/L
Primary indications for humidification therapy
- humidifying dry medical gases
- overcoming humidity deficit created when upper airway is bypassed
Secondary indications for humidification therapy
- treating bronchospasm caused by cold air
- managing hypothermia (reducing body temperature)
Clinical signs and symptoms of inadequate airway humidification
- atelectasis
- dry, nonproductive cough
- increased airway resistance
- increased incidence of infection
- increased work of breathing
- patient complaint of substernal pain and airway dryness
- thick, dehydrated secretions
- destruction of the airway epithelium
4 Physical principles governing humidifier function
- temperature
- surface area
- time of contact
- thermal mass
Temperature
the higher the temperature of gas, the more water it can hold
Surface area
affects rate of evaporation
- greater the surface area of contact between water and gas, more opportunity there is for evaporation to occur
Passover humidifier
pass gas over a large surface area of water
Bubble diffusion
directs a stream of gas underwater, where it is broken up into small bubbles
Wicks
use porous water-absorbent materials to draw water (similar to a sponge) into its fine, honeycombed structure by means of capillary action
Time of contact
evaporation increases as contact time increases
- longer gas remains in contact with water, greater the opportunity for evaporation to occur
- for bubble humidifiers, contact time depends on the depth of water column
- passover and wick-type humidifiers, the flow rate of gas through humidifier is inversely related to contact time
(with high flow rates reducing the time available for evaporation to occur)
Thermal mass
the greater the amount of water in humidifier, the greater the thermal mass and capacity to hold and transfer heat to therapeutic gas
Active humidifier
actively adding heat of water or both to the device-patient interface
- bubble humidifiers, passover humidifiers, nebulizers or bland aerosols, and vaporizers
Passive humidifier
recycling exhaled heat and humidity from the patient
- typical heat and moisture exchangers (HMEs)
Bubble humidifiers
- breaks underwater gas stream into small bubbles
- use of foam or mesh diffuser produces smaller bubbles than open lumen, allowing greater surface area or gas/water interaction
- usually used unheated with oxygen delivery systems to raise water vapor content of gas to ambient levels
- includes simple pressure relief valve
- can produce aerosols at high flow rates
- unheated bubble humidifiers can provide AH levels b/w approx. 15 - 20 mg/L
Passover humidifiers
- directs gas over water surface
1. simple reservior
2. Wick type - absorbent material increases surface area for dry ir to interface with heated water
3. membrane type - separates water from gas stream by means of hydrophobic membrane
Heat-moisture exchangers
- often passive humidifier that has been described as “artificial nose”
- captures exhaled heat and moisture and returns up to 70% of heat and humidity to patients during next inspiration
- HMEs do not actively add heat or water to the systems
Types of HMEs
- simple condenser humidifiers
- hygroscopic condenser humidifiers
- hydrophobic condenser humidifiers
Simple condenser humidifiers
- contain a condenser element with high thermal conductivity, usually consisting of metallic gauze, corrugated metal, or parallel metal tubes
Hygroscopic condensor humidifiers
Absorbs moisture from air by using materials that:
- incorporate condensing element of low thermal conductivity (helps retain more heat)
- impregnating this material with a hygroscopic salt (helps capture extra moisture from exhaled gas)
Hydrophobic condenser humidifiers
- use a water-repellent element with a large surface area and low thermal conductivity
- on exhalation the condenser temp increase to 25C and provides evaporation of water
- on inhalation cool gas and evaporation reduce the condenser temp at 10C which causes more uptake of evaporated water
- on exhalation the condenser temp increase to 25C and provides evaporation of water
HMEs add ____ ml of dead space
5 - 90 ml
Active HMEs
add humidity or heat or both to inspired gas by chemical or electrical means
Humid-heat
- absorbs expired heat and moisture and releases it into inspired gas
- consists of supply unit with microprocessor, water pump, and humidification device
HME booster
- designed for patients with minute volumes of 4-20 L
- no appropriate for pediatric patients with infants
- consists of T-piece containing electrically heated element
Heat ____ water output of bubble and passover humidifiers
improves
When are heated humidifiers primarily used?
primarily used for patients with bypassed upper airways and those receiving mechanical ventilation
Types of heating elements that require energy source
- hot plate
- wraparound type
- yolk, or collar element
- immersion type heater
- heated wire
- thin-film, high-surface area broiler
- servo-controlled heating system that monitors temp. at or near patients airway using thermistor probe
Manual systems
- simple large reservoir systems are manually opened and refilled with sterilization or distilled water; cross- contamination can occur
- small inlet can be attached to gravity-fed intravenous bag and line allows refilling without interruption
Automatic systems
- avoid need for constant checking and manual refilling
- flotation valve controls can be used to maintain humidifier reservoir fluid volume
At least ____ of humidity is recommended for intubated patients
30 mg/L
Some experts recommend heating inhaled gas to maintain airway temperature near _____ to _____
35C to 37C
AARC guidlines reccomends ___C, wishing ___C, with a minimum of ____of water vapor
33C, 2C, 30mg/L
What occurs due to temperature difference across the system
condensation
Factors influencing the amount of “rain out”
- temp. difference from humidifier to airway
- ambient room temp.
- gas flow
- set airway temp.
- length, diameter, thermal mass of breathing circuit
Risks for rain out
- can waste a lot of water
- can occlude gas flow through circuit
- can be aspirated
- condensate may be colonized with bacteria
Avoid cross-contamination
- water in circuit can be source of bacterial colonization
- minimizing condensation
- heated-wire circuits
- wick or membrane passover humidifiers
- frequently change circuits is NOT needed to reduce chance of nosocomial infection
ensure proper conditioning of inspired gas received by patients by:
- regularly measuring patients FiO2 levels
- providing ventilatory care and monitoring selected pressures, volume, flows
- using hygrometer- thermometer system
aerosol generators include:
large volume jet nebulizers and ultrasonic nebulizers
Indications of bland aerosol therapy
- presence of upper airway edema
- laryngotracheobronchitis
- subglottic edema
- postextubation edema
- postoperative management of upper airway
- presence of a bypassed upper airway
- need for sputum
Contradictions of bland aerosol therapy
- bronchoconstriction
- history of airway hyperresponsiveness
Hazards and complications of bland aerosols therapy
- wheezing or bronchospasm
- infection
- overhydration
- patient discomfort
- caregiver exposure to airborne contagions
- edema of the airway wall
What is the most common device used for bland aerosol therapy
Large volume jet nebulizers
Unheated LVN can produce ___ to ___ mg H2O/L
26 to 35
Heated LVN can produce ___ to ___ mg H2O/L
35 to 55
what device is electrically powered that uses piezoelectric crystal to generate aerosols
ultrasonic nebulizer
Crystal transducer converts radio waves into high-frequency mechanical vibrations that produce aerosol
ultrasonic nebulizer
Types of airway appliances
- aerosol mask
- face tent
- t-tube
- tracheostomy mask
Problems with bland aerosol therapy
- cross-contamination and infection
- environmental exposure
- inadequate aerosols output
- overhydration
- bronchospasm
- noise
Key considerations of selecting appropriate therapy
- gas flow
- presence or absence of an artificial tracheal airway
- character of pulmonary secretions
- need for and expected duration of mechanical ventilation
- contraindications to using an HME
