Chapter 35 Humidifiers

A HME has been describes as what?

"artificial nose"

The efficiency of the bubble humidifier depends on what?

(contact) water level in reservoir.

Name the 2 primary indications for humidification therapy.

1) Humidifying dry medical gases 2) Overcoming the humidity deficit created when the upper airway is bypassed

Name th secondary indications for humidification therapy.

1) Managing hypothermia 2) Treating bronchospasm caused by cold air

Name factors that can shift the ISB deeper into the lungs.

1) When a person breathes through the mouth rather than nose, the ISB shifts distally. 2) Breathing cold, dry air. 3) Upper airway is bypassed. (breathing through artificial tracheal airway) 4) Minute ventilation is higher than normal.

Name more space-efficient ways to increase the water/gas surface-area ratio.

1) bubble diffusion 2) aerosol 3) wick technologies

Name the 3 primary types of humidifiers.

1) bubble humidifiers 2) passover humidifiers 3) HME (heat and moisture exchangers)

Hygroscopic condenser humidifiers provide higher efficiency by using what?

1) condensing element of low conductivity (paper, wool, foam) 2) impregnating material with a hygroscopic salt (calcium or lithium chloride)

Prolonged breathing of improperly conditioned gases through a tracheal airway can result in conditions?

1) hypothermia 2) inspissation of airway secretions 3) mucociliary dysfunction 4) destruction of airway epithelium 5) atelectasis

If oxygen fails to flow from the humidifier, what should you check?

1) is flowmeter turned on 2) if pre-filled, make sure the reservoir has been pierced and that gas can flow through it 3) check the outlet for obstruction 4) check the oxygen tubing for obstruction or kinks 5) replace the humidifier

What are some advantages of passover humidifiers over bubble humidifiers?

1) maintain saturation at high flow rates - unlike bubble 2) add little or no flow resistance to spontaneous breathing circuits 3) do not generate any aerosols 4)thus, minimal risk for infection

Name the 3 types of HMEs.

1) simple condenser 2) hygroscopic condenser 3) hydrophobic condenser

Name 3 variables that affect the quality of a humidifier's performance.

1) temperature 2) surface area 3) time of contact

Name the 3 common types of passover humidifiers.

1) the simple reservoir type 2) the wick type 3) the membrane type

Name conditions that warm, humidified gases are used to treat or prevent.

1) treatment of hypothermic patient. (raises core temperatures back to normal) 2) prevent intraoperative hypothermia 3) alleviate bronchospasm in patients who develop airway narrowing after exercise or breathing cold air

Unheated bubble humidifiers have limited effectiveness at flow rates higher than what?

10 L/min

At room temperature, unheated bubble humidifiers can provide absolute humidity levels of what?

15 - 20 mg/L

What is the pharyngeal temperatures when a person inhales through the mouth?

3 degrees less than when breathing through the nose, with 20% less relative humidity

At body temperature and pressure saturated, inspired gas is what?

37 degrees C, contains 44 mg/L of water and exerts a partial pressure of 47 mmHg and is fully saturated

Administration of dry medical gases to the upper airway should never have flows great than what?

4 L/min

When inspired air is fully saturated (100%) at 37 degrees C it holds what?

44 mm H2O per liter of gas and exerts a water vapor pressure of 47 mmHg

What is the capacity of water at body temperature?

44 mm/L

How much of a patient's exhaled moisture can a simple condenser humidifier recapture?

50%

What is the formula for calculating Absolute Humidity?

AH = RH x mg H2O/L =

What is the actual content or weight of water present in a given volume of gas and is expressed in mg/L?

Absolute Humidity

Specifications covering the design and performance requirements for medical humidifiers are established by who?

American Society for Testing and Materials (ASTM)

What is the formula for calculating Body Humidity?

BH = absolute humidity ----------------------- x 100 44 mg/L

What conditions does gas moving into the lungs achiev e?

BTPS - body temp 37 degrees C, barometric pressure, saturated with water pressure (100% RH at 37 degrees C)

What is Relative Humidity at body temperature and is expressed as a %?

Body Humidity

What is the most common of the disposable humidifiers used in Respiratory Care?

Bubble Humidifier (non-heated)

Room humidifiers work off of what principle?

Centrifugal Force (spinning). Electrically powered.

What is the formula for calculating Humidity Deficit?

HD = Body Humidity - actual humidity (mg/L) or as a % deficit --------- x 100 44 mg/L

What is the physiologic term that refers to the difference between inspired gas's water content and the water content of a gas at body temperature.

Humidity Deficit

Shifts is the ISB affect the body's normal heat and moisture exchange mechanism resulting in the need for what?

Humidity Therapy

What happens to air as it reaches the carina?

It has been warmed to body temperature of 37 degrees C and is 100% saturated

Does bubbling occur in the membrane-type humidifier?

No

Does bubbling occur with wick humidifiers?

No

If a membrane-type humidifier were inspected while in use, would liquid water be seen in the humidifier chamber?

No

What is the simplest of all humidifiers?

Pass-Over humidifier (non-heated)

What is the formula for calculating Relative Humidity?

RH = Absolute (content) humidity ----------------------------------- x 100 Capacity

What does "inspissated" mean?

Thickened due to dehydration

Is the mouth less effective than the nose for heat and moisture exchange?

Yes

Would a clogged inlet prevent the pop off alarm from sounding?

Yes

What is a humidifier?

a device that adds molecular water to gas

Any device that generates an aerosol, poses what?

a high risk of spreading infection

Failure of a pop-off to sound, may be an indication of what?

a leak of faulty pop-off valve

In cold weather, the formation of condensates exceed the ability of mucus to reabsorb water results in what?

a runny nose

What does "active" mean?

actively adds heat and /or water to the device-patient interface

Humidity Therapy

adding water to vapor and (sometimes) heat to the inspired gas

No bubbling means what is not produced?

aerosol

At high flow rates, what can bubble humidifiers produce?

aerosols

What should the inspired humidity be when given though a tracheal airway?

at least 60% of BTPS conditions

Delivery of cool humidified gases are mostly used with what?

bland aerosol delivery

Humidifier pop-offs should provide what?

both an audible and visible alarm and should automatically resume normal position when pressures return to normal

How does a humidifier add molecular water to gas?

by evaporation of water from a surface

Breathing dry gas through an endotracheal tube can cause what?

damage to tracheal epithelium within minutes

Above the ISB, temperature & humidity during inspiration & exhalation do what?

decrease during inspiration. increase during exhalation

Why is the Pass-Over Humidifier low humidification?

decreased contact time. limited surface area

Explain the bubble-diffusion technique.

directs a stream of gas underwater, 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 is the water/air surface-area.

The greater the area of contact between water and gas gives opportunity for what?

evaporation to occur

Condensation occurs on the mucosal surfaces during what?

exhalation

How does the nose affect normal airway humidification?

filters, warms, and humidifies inspired air

If the alarm sounds without intentional occlusion, what may be the problem?

gas flow is too high. kink in the tubing. obstruction at the outlet.

The mouth is less efficient in reclaiming what?

heat and water

What are simple reservoir type used with and for?

heated fluids for use with mechanical ventilation. may be used with room temperature fluids with noninvasive ventilatory support (nasal continuous positive airway pressure or bilevel ventilation)

What does the hygroscopic salt do?

helps capture extra moisture from the exhaled gas

Simple condenser humidifiers contain a condenser element with what?

high thermal conductivity, usually with metallic gauze, corrugated metal, or parallel metal tubes

A membrane-type humidifier separates the water from the gas stream by means of a what?

hydrophobic membrane

How is Relative Humidity measured?

hygrometer

What effect do dry medical gases administered to the upper airway at more than 4 L/min cause?

immediate heat and water loss. structural damage to the epithelium if prolonged

What is the name of the point where inspired gas achieves BTPS?

isothermic saturation boundary (ISB)

During exhalation, the relative humidity of expired gas varies little between what?

mouth and nose breathing

What happens if the down tube becomes obstructed?

no bubbling or alarm will occur. Compensated flow meter will read ZERO

How do aerosols spread infections?

not visible to the naked eye, the water-droplet suspensions can transmit pathogenic bacteria from the humidifier reservoir to the patient

What are unheated bubble humidifiers commonly used with?

oronasal oxygen delivery systems

How do passover humidifiers work?

pass gas over a large surface area of water

The typical HME is a _________ humidifier.

passive

How is proper function checked?

pinching the connected tubing and listening for the alarm

At what point does inspired gas achieve BTPS?

point approximately 5 cm below the carina

What do wick technologies use to increase surface are?

porous water-absorbent materials

What does "passive" mean?

recycles exhaled heat and humidity from the patient

Below the ISB, temperature and relative humidity what?

remain constant (BTPS)

What should be done if water is low in a bubble humidifier?

replace set-up if disposable. refill with sterile water if permanent

What is the benefit of using a condensing element of low thermal conductivity?

retain more heat unlike simple condenser humidifiers

Why is it important to keep room humidifiers clean and change the water in the reservoir frequently?

source of nosocomial infections. large reservoir is source for bacterial growth

What is an alternative to dispersing gas bubbles in water?

spraying water particles into the gas by generating an aerosol in the gas stream.

What is an aerosol?

suspension of water droplets

For bubble humidifiers, what does the contact time depend on?

the depth of the water column: the deeper the column, the greater the time of contact as the bubbles rise to the surface.

Why is temperature important in a humidifier?

the greater the temperature of a gas, the more water vapor it can hold (increased capacity)

Why is contact time important?

the longer a gas remains in contact with, the greater the opportunity for evaporation to occur.

The primary goal of humidification is to maintain normal physiologic conditions in what?

the lower airways

What is Relative Humidity?

the ratio between the amount of water in a given volume of gas and the maximum amount its capable of holding at that temperature. Humidity expressed as a percentage of a gas's capacity (water content when fully saturated)

Heat and moisture exchange is a primary function of......

the respiratory tract, mainly the nose

Why shouldn't the reservoirs of bubble humidifiers be heated?

the resulting condensate tends to obstruct the small bore delivery tubing to which they connect

The amount of heat and humidity the patient needs depends on what?

the site of gas delivery

How much heat and moisture does an HME return to the patient during their next inspiration?

up to 70%

What is the delivery of cool humidified gas used to treat?

upper airway inflammation resulting from: 1) croup 2) epiglottitis 3) postextubation edema

How does the "hydrophobic" membrane work?

water vapor molecules can easily pass through this membrane, but liquid water (and pathogens) cannot.

How may a patient reduce cold-air induced bronchospasm?

wearing a scarf over nose and mouth when outside in cold weather

How do wick technologies work?

wick draws water into its fine honeycombed structure by means of capillary action.